Patent Application
20240310615
This application claims benefit to the following European Patent Application Nos.: i) EP 23158510.0, filed on Feb. 24, 2023, ii) EP 23158559.7, filed on Feb. 24, 2023, iii) EP 23158561.3, filed on Feb. 24, 2023 and iv) EP 23159969.7 filed on Mar. 3, 2023, the entire disclosures of which are hereby incorporated by reference herein.
The present disclosure relates to a keratoscope relay mechanism for an optical coherence tomography (OCT) scanner having a compact design suitable for mounting to the undercarriage of a microscope and related aspects.
OCT is performed using an optical instrument which allows the generation of a cross-sectional image of biological tissue. It is possible to achieve axial resolutions well below 8 microns using monochromatic light having a constant phase difference which allows OCT scans to be useful in probing living tissue (in vivo) as well as in other applications. As OCT scans cannot necessarily penetrate to a great depth they are particularly useful for probing skin tissues and in ophthalmology. To generate an image with depth information, the OCT scanner generates a number of one-dimensional scans, known as A-scans, are performed along a scan line and when stacked together these A-scans create a two-dimensional image, known as a B-scan. By acquiring B-scans sufficiently closely and rapidly a volumetric image of a OCT probed sample tissue can also be obtained.
To generate three-dimensional images, OCT scanners scan a sample using a beam path across two dimensional spatial locations. Such scanning systems known in the art typically use orthogonal galvanometer mirrors to address the desired two dimensional spatial locations of the sample. To avoid Petzval curvature of the resulting interferometric image plane caused by the spatial separation of the galvanometer mirrors, relay optics may be required to combine the pupil of each scanning mirror to a common pupil which can then be focused to an image plane of common optical path length for each galvanometer mirror. Alternatively, electromechanical 2D scanning mirror systems are also known in the art which use a single pupil for each scan axis, but these operate at a much reduced scan speed due to physical size restrictions of the technology, making them less desirable than systems which can scan at higher speeds.
OCT scanners are available for use in a variety of surgical procedures where depth information is advantageous. For surgical procedures on small areas, or where access to the tissue region being operated on is restricted, for example when using OCT scanners during eye surgery, the form factor of the OCT scanner needs to be very different from the form factor of an OCT scanner where access is not restricted or no access is required to the region being probed by the OCT scanner whilst the OCT scan is ongoing.
Scanning systems typically use two orthogonal galvanometer mirrors separated in space to address the desired 2D spatial locations of a sample. In order to produce a flat tomographic image plane, the spatial separation of the galvanometer mirrors require relay optics which combine the pupil of each scanning mirror to a common image pupil. However, known systems have large formats as a result and such multi optical element scanner designs are less desirable for intraoperative systems requiring a minimal sterile field volume.
It is known for OCT systems which depend on galvanometric scanning mirrors due to their fast response times to use integrated optical feedback so that closed loop operation is possible. Two axis scanning requires two galvanometric scanning mirrors, one for each scanning axis, and which must be spatially separated due then to mechanical limitations. For 2D scanning mirrors such as MEMS devices an orthogonal angle of incidence is typically used to avoid geometric distortions in the resultant scan patterns.
The use of OCT scanners when performing surgical procedures creates additional design constraints for the form factor of the OCT device. On such limitation is a physical limitation on the size of the combined microscope and OCT adapter. For example, the overall height of the OCT device and any attached microscope being used by a surgeon performing a surgical procedure is limited by design so that a surgeon can view the area being scanned through the microscope whilst still accessing the area under the OCT/microscope using surgical tools for performing the surgical procedure.
Micro-electromechanical systems (MEMS), based optically reflective devices can be used to reduce the physical size restrictions of scanning mirror assembly and support higher scan rates but with much smaller clear apertures. Small clear aperture optical designs for OCT applications have been used in the past though with either low numerical apertures resulting in low lateral resolution at the image plane or complicated design results due to the use of convergent light beams incident on small aperture MEMS mirrors.
In applications such as metrology or intraoperative OCT, which benefit from a flat tomographic image plane, the spatial separation of the galvanometer mirrors require relay optics to combine the pupil of each scanning mirror to a common pupil which is then focused to an image plane. This results in large format, multi optical element scanner designs which are less desirable for intraoperative systems requiring a minimal sterile field volume. Optical designs based on small aperture reflective scanners result in low numerical aperture designs resulting in low lateral resolution or complicated optical designs due to the use of convergent light beams at high incident angles on small aperture MEMS mirrors.
The design of OCT scanning systems for surgery is accordingly subject to a variety of design constraints, particularly OCT scanning systems for eye surgery where the OCT light must access the eye interior via the pupil of the eye. Using an OCT scanner during eye surgery may impose a variety of design constraints which may be in tension with each other. In order to keep the microscope height, or other dimension of the device between the surgeon and the orientation of the tissue being operated on and depending on the form factor of the microscope, as short as possible, it is known in the art to replace the microscope objective lens with an objective lens which is part of an OCT scanner system. The OCT scanner system objective lens is aligned with the optical channel of the microscope optics and this allows the OCT scanner to use the same focal plane as the microscope uses. However, known OCT microscope adapter systems such as the Leica EnFocus™ scanner, have a form factor which currently adds around 50 mm or so at best to the stack height of the microscope when they are attached. The scanner is under carriage mounted with a side entering optical path reflected to the focal plane via a beam splitter set at an angle of incidence of 38 degrees, through the centre of the objective lens which results in a parallax alignment relative to the ocular optical channels and a large stack height due to the size and angle of incidence of the required beam splitter.
The inventors of the present application recognize that it is desirable accordingly to improve the optical design of OCT adapters allow for a more compact form factor both laterally and vertically. By vertically minimising the height of the microscope and OCT adapter assembly when they are fixed to each other, and by keeping the OCT adapter laterally to within the footprint of the microscope, more access to the area being probed by the OCT scan whilst a scan is ongoing may be provided. Advanced functionality contained in current ophthalmic surgical microscopes often includes a Keratoscope illumination source mounted concentric to the objective lens mounted on the undercarriage of the surgical microscope. This light source can consist of a series of individual LEDs arranged in a circle of a slightly larger diameter than that of the objective lens that project light onto the cornea of a patient under treatment. When imaged through the microscope, the ring of light forms a corresponding reflection from the surface of the cornea. Given that the geometric pattern from the Keratoscope illumination LEDs is circular, the corresponding shape of the surface reflection from the cornea is indicative of the cornea curvature itself.
Current under carriage mounted OCT scanners however obscure the keratoscope illumination and thus render the functionality unusable.
In an embodiment, the present disclosure provides a keratoscope relay mechanism for an OCT scanner adapter configured as a microscope accessory for a microscope. The relay mechanism includes a plurality of light emitting diodes (LEDs) including a ring arrangement, the LED ring arrangement forming a keratoscope ring replicating an arrangement of a plurality of keratoscope LEDs of the microscope; a pair of photo detectors, each photo detector aligned with a different LED of the microscope keratoscope LEDs, at least one of the different microscope keratoscope LEDs being activated in a fixation keratoscope mode; and a light sealing gasket including two apertures aligned with the photo detectors. Based on the photo detectors detecting a keratoscope state of the microscope keratoscope LEDs, a corresponding keratoscope state of the LEDs of the keratoscope ring is activated.
Subject matter of the present disclosure will be described in even greater detail below based on the exemplary figures. All features described and/or illustrated herein can be used alone or combined in different combinations. The features and advantages of various embodiments will become apparent by reading the following detailed description with reference to the attached drawings, which illustrate the following:
The following summary statements set out features, which may be preferred features in some embodiments, of the present invention.
Embodiments of the present invention can mitigate or obviate at least some of the above mentioned design limitations of known OCT scanner adapters for microscopes. For example, in an embodiment a keratoscope relay can automatically activate a keratoscope mode of a compact OCT scanner adapter to emulate the keratoscope mode activated on the microscope.
Example embodiments of the disclosed OCT scanner adapters are able to be under carriage mounted as an accessory to a microscope such as a surgical microscope and in some embodiments are provided with a keratoscope relay. The Keratoscope relay capability retains complete functionality of a microscope keratoscope while also providing completely seamless operation, as there is no need to send any control signals or commands to activate the keratoscope between the surgical microscope and the OCT scanner adapter.
Advantageously, the embodiments of the present invention can enable a compact OCT scanner having an improved MEMS-based optical design for a scanning mirror assembly suitable for OCT scanner applications to be used with keratoscope functionality.
A first aspect of an embodiment of the present invention comprises a keratoscope relay mechanism for an optical coherence tomography, OCT, scanner adapter configured as a microscope accessory for a microscope where the relay mechanism comprises a plurality of light emitting diodes, LEDs, having a ring arrangement, the LED ring arrangement replicating an arrangement of keratoscope LEDs of the microscope, a pair of photo detectors, each photo detector aligned with a different LED of the microscope keratoscope LEDs, at least one of the different microscope keratoscope LEDS being activated in a fixation keratoscope mode, and a light sealing gasket comprising two apertures aligned with photodetectors, wherein responsive to the photodetectors detecting a keratoscope state of the microscope keratoscope LEDs, a corresponding keratoscope state of LEDs the keratoscope ring is activated.
In some embodiments, the ring is provided around an objective lens of the OCT scanner adapter, wherein the objective lens functions as a microscope objective lens when the OCT scanner adapter is attached to the microscope.
In some embodiments, the photodetectors are aligned with orthogonally spaced LEDs of the microscope. By detecting when the orthogonally spaced LEDs of the microscope are activated there is less chance of light leaking from one of the gasket apertures and causing the photodetector aligned with the other gasket apertures from accidentally activating and triggering a wrong keratoscope mode on the OCT adapter ring.
In some embodiments, a corresponding keratoscope state of LEDs of the keratoscope ring which is activated based on the photodetectors detecting a corresponding state of the keratoscope LEDs on the microscope comprises one of the following keratoscope states, a keratoscope off-state, a keratoscope fixation mode state, a keratoscope full illumination state, and another type of keratoscope on-state.
Examples of the other type of keratoscope on-state include a flashing LED on-state or a change of colour on-state of the LEDs.
Another aspect of an embodiment of the present invention comprises an optical coherence tomography, OCT, scanner adapter configured as a microscope accessory for a microscope, the scanner adapter including a keratoscope relay mechanism according to the first aspect or any of its embodiments disclosed herein.
In some embodiments, the keratoscope relay mechanism comprises a plurality of light emitting diodes, LEDs, having a ring arrangement around an objective lens of the OCT scanner adapter, the LED ring arrangement replicating an arrangement of keratoscope LEDs around an objective lens of the microscope, a pair of LED light detectors located at different point around the LED ring, a gasket which prevents keratoscope LED light from the microscope entering the objective lens of the OCT scanner adapter, the gasket comprising two apertures aligned with photodetectors via which microscope keratoscope light is detectable by the photodetectors, where responsive to a keratoscope state of the microscope keratoscope LEDs being detected by the photodetectors, a corresponding keratoscope state of the keratoscope ring of the OCT scanner adapter is activated.
In some embodiments, the OCT adapter comprises a housing, a plurality of optical components contained in the housing, the optical components comprising at least a scanning mirror assembly, a folding mirror, a beam splitter and an objective lens, wherein the beam splitter and folding mirror are arranged to direct a scanning light beam emerging from the scanning mirror assembly through the objective lens offset from the central optical axis of the objective lens.
In some embodiments, the objective lens is configured to be collinear with an optical channel of the microscope when the OCT scanner adapter is attached to an undercarriage of the microscope.
In some embodiments, the optical components are housed within a housing having a height, h2, less than 40 mm.
In some embodiments, the optical components are housed within a housing having a height, h2, of about 36 mm.
In some embodiments, the OCT scanner adapter is configured as an accessory for a surgical microscope used for eye surgery.
In some embodiments, the OCT scanner adapter comprises features from or forming any one of the embodiments of an OCT scanner adapter disclosed herein.
In some embodiments, the OCT scanner adapter forms part of a scanning or probe arm of an OCT scanning system according to any one of the embodiments of an OCT scanning system disclosed herein.
Advantageously, embodiments of the disclosed OCT scanner adapter may include an example embodiment of a MEMS scanning mirror assembly having a design according to an embodiment disclosed. Such a design may limit the lateral size of the OCT adapter to below the footprint of a surgical microscope optics carrier housing.
Advantageously, embodiments of the disclosed OCT scanner adapter may include an example embodiment of a compound angle beam-splitting arrangement having a design according to an embodiment disclosed. The OCT beam-splitting arrangement allows the attached OCT scanner objective lens to be vertically highly compact which reduces the height of the OCT scanner adapter.
This is useful when eye surgery requires the surgeon to use the microscope or similar device to generate an enlarged image of the area of operation using microscope optics so that the surgeon is able to better see the area being operated on whilst still keeping the patient within the surgeon's arm's reach.
In other words, some embodiments of the OCT scanner system design disclosed herein result in a combined stack height of the microscope and attached OCT adapter which is far shorter than previously possible. The design better balances the design constraints and allows a surgeon to view an area being scanned by the OCT scanner via an eye piece or eye pieces of the microscope and keep the area being scanned in the focal plane of the microscope optics whilst still allowing the surgeon to physically reach the scanned area to perform a surgical operation.
Other aspects of embodiments of the present invention can provide additional benefits. For example, some embodiments of the OCT scanner adapter use a closed-loop feedback system to increase the B-scan rate of the OCT scanning system which allows for live stream of OCT video to be generated which may be particularly useful when the OCT scanner adapter is attached as an accessory to a surgical microscope as it allows live feedback on the region being scanned whilst an operation is ongoing.
Some embodiments of the scanning mirror assembly reflects the beam used for feedback on the scanning mirror position in the feedback system in a different optical plane from that used by the OCT scanning beam which may reduce the likelihood of returned light from the feedback arm contaminating the mirror position reference beam or its optical source or contaminating the OCT scanning beam and enables a high signal to noise to be achieved when detecting the mirror positioning beam.
The above aspects and/or examples disclosed herein above and later below may be suitably combined with each other as would be apparent to anyone of ordinary skill in the art.
The detailed description set forth below provides examples of embodiments of the present invention which are explained in sufficient detail to enable those skilled in the art to put embodiments of the present invention into practice.
There are two forms of OCT scanning, time-domain OCT (TD-OCT) and spectral domain OCT (SD-OCT). SD-OCT uses spectral interrogation of the spectrum at the OCT interferometer output.
In the example SD-OCT system 100 illustrated in
It will be apparent that the system 100 is illustrated in
In the following, references to an OCT scan image or image data may refer to a one-dimensional A-scan or to a two-dimensional B-scan comprising a plurality of A-scans or to a volumetric scan image comprising a plurality of B-scans where appropriate as would be apparent to someone of ordinary skill in the art.
As illustrated in
The different phase shifts between the reference arm returned OCT light and the OCT returned from the probe arm which result in the interference pattern detected, arise because the OCT light is returned from one or more different structures at different depths on or within the scanned tissue sample 116. In some embodiments, the scanned tissue sample may instead comprise a different type of object of interest 112 to an in-vivo tissue sample located in an area of the human body.
The phase shift which generates the interference is affected by the different depths at which the OCT light is returned by structures within the sample scanned. The interference from the phase shift allows the signal output 146 of the spectrometer 136 to be used to generate images known as tomographs which provide a visual indication of the depth of one or more such structures in the scanned or probed area and their location in the scanned or probed area.
In some embodiments of the SD-OCT system 100 shown in
The probe OCT beam is returned after it has been back-scattered or reflected or otherwise returned from any structures at a certain depth in the area 116 including the tissue sample being scanned. In some embodiments, one or more or all of the optical paths 101a, 103a, 105a, 107a, are provided using suitable single-mode optical fibres and may include one or more sections where a beam following the optical fibre travels in free space.
In the embodiment of the SD-OCT system 100 illustrated schematically in
In some embodiments, the interference between the returned reference beam and returned OCT probe beam light which occurs along the output arm 107 is measured using a suitable spectrometer 136 such as that shown in
In some embodiments of the OCT system 100, one or more or all of the optical paths 101a, 103a, 105a, 107a, comprise suitable single-mode optical fibres and/or include one or more sections where an outward or inward (relative to the coupler 104) OCT beam following an optical fibre travels in free space.
In some embodiments of the present invention, although the optical path lengths followed by the reference beam and probe beam are matched, the dispersive properties of the optical fibre each beam travels along are configured to differ to improve the removal of a complex conjugate image from the OCT image output and so improve the image quality of the OCT scan image and the speed at which a complex conjugate resolved OCT scan image is obtained.
In some embodiments, the term OCT scan is used herein to refer to a B-scans and volumetric scan images of the tissue area (also referred to herein as a tissue sample) 116 which are generated using the spectral domain, SD-OCT scanner system 100.
In the example shown schematically in
The spectrometer 136 shown in
The spectrometer 136 of the embodiment of the SD-OCT system 100 shown in
The OCT probe beam follows an optical path 105a from the coupler 104 along the OCT probe branch 105 of the coupler 104 after which it enters an OCT scanner 164. The example OCT scanner 164 shown in
The scanning mirror 112 may comprise a microelectromechanical system, MEMS, scanning mirror which is moved angularly by a mirror mover. The movement of the scanning mirror 112 moves the OCT probe beam across the sample or other object of interest being scanned and the resulting interference pattern generated is used to generate an OCT B-scan image from the system output 156.
The movement of the mirror mover is performed under the control of a controller 162. The controller 162 may be located in scanning mirror assembly which includes the scanning mirror 112 or located remotely from it.
The mirror position system 156 shown in
As the scanning mirror 112 is moved in use of the OCT scanner 164 by the mirror mover mechanism under the control of the controller 162 to guide the OCT beam along a scan path. After reflection by the mirror 112, the OCT probe beam passes through a telecentric objective lens 114 which focusses the OCT probe beam at different locations in a focal plane 154 at the sample tissue 116 which is being scanned. As shown schematically in
The telecentric objective lens 114 via which the probe beam passes to reach sample 116 and via which returned probe beam light also passes is shown in
The scanned area comprises a sample of tissue 116. In
For example, as shown in
The likelihood of a successful outcome from a surgical procedures performed on tissue such as the human eye, or the eye of another creature, where there is very limited access may be improved by using OCT. The OCT system 100 may be used in some embodiments to create images based on two or three-dimensional scans of region of an eye 116 as it is being operated on and these can be presented in real-time to the person performing the operation. This can allow the depth of any procedure being performed is better understood as the surgery takes place. Providing this depth information for an area subject to a surgical procedure in real-time may help a surgeon avoid making an incision which is too deep (which may damage underlying tissue unnecessarily) or one which is too shallow (in which case the operation may not be a success and/or the tissue being operated on may take longer to heal).
As is shown schematically in
Display 152 may be part of the apparatus hosting the SD-OCT system 100 performing the image processing or a different apparatus. Some example embodiments of the present invention generate a series of OCT scan images 148 using an OCT probe light beam sufficiently quickly to provide a live-stream video comprising OCT scan images 150 on display 152. Display 152 may be a near-eye display in some embodiments. In some embodiments display 152 may be a large display system comprising a plurality of displays to present information both to the surgeon and/or to others in the operating theatre. A display 152 may be integrated into the SD-OCT system 100 or be external to it.
One or more of the components shown in
In some embodiments, the OCT scanner system 100 comprises an OCT scanner 164 provided as an adapter for a microscope, for example, the OCT scanner adapter 206 for the microscope 200 shown schematically in
Example(s) of Microscope System with an OCT Scanner Adapter
In some embodiments, the OCT scanner adapter 206 has a form factor which is vertically compact so that it does not add too much height h2 to the microscope height h1 that it is attached to in use. By reducing the additional vertical height h1 of the OCT scanner adapter 206, the ease of access to the scanned area during use of the scanner when generating cross-sectional images of the scanned area 116 whilst the microscope is concurrently used is improved. The OCT scanner adapter 206 is also laterally compact. This means that when attached to the microscope 200 it does not unduly hinder surgical access to the area of tissue being scanned which allows a surgical procedure to be performed at the same time.
In the description below, reference is made to height in the context that an OCT scanner adapter 206 will be used to scan a tissue sample 116 from a location above the tissue sample, such as may result when the OCT scanner adapter 206 is mounted to the undercarriage of the surgical microscope 200.
Some embodiments of the OCT scanner 206 described herein may retain a similarly compact form factor and be used in other contexts. Moreover, the OCT scanner 206 may be provided in some embodiments integrated into another apparatus such as microscope 200. In some embodiments, OCT scanner 206 may be distributed as an optional accessory for such apparatus such that it may be distributed and sold independently of the microscope it is later attached to when in use. Accordingly, unless the context clearly prohibits it, references to height may apply equally to other dimensional directions of the OCT scanner which are substantially or approximately orthogonal to the plane of the OCT objective lens and any apparatus to which the OCT scanner is attached and the orientation of the OCT scanner and microscope stack may differ also depending one or more of a patient orientation and configuration of microscope optics and eyepiece location.
In other words, reference to height in the context of overall “height” is merely based on the assumed orientation of the OCT scanner and microscope relative to a supine patient that when surgery is being performed on the patient. Whilst a patient is supine, a surgeon may access the area being operated on below an embodiment of an OCT scanner adapter 206 according to the present invention whilst at the same time having physical access to the eyepiece of the microscope 200 to which the OCT scanner 206 is attached. This geometric configuration may be varied in some embodiments depending on the configuration of the microscope optics and/or orientation of the patient and/or location of the area being operated on. Accordingly, in the description below references to the height and/or combined stack height of the microscope and OCT scanner adapter 206 may also refer to other dimensions of the microscope and OCT scanner adapter 206 which act as a constraint on the form factor of the OCT scanner where this would be apparent to someone of ordinary skill in the art.
Returning now to
In the example embodiment of the OCT scanner adapter 206 shown in
Also shown in
OCT scanning light is returned from the OCT scanner adapter 206 via the optical port 214 in some embodiments to the interferometry components of a OCT scanning system 100 such as that shown in
For example, in the embodiment of
After emerging and illuminating the sample tissue 116 being scanned, OCT light is reflected, back-scattered or otherwise returned. The returned OCT light then passes back through the coupler 104 where it interferes with light returned from reference arm 103. The returned OCT and reference beams then propagate along output arm 107 to spectrometer 136 which outputs the OCT and reference beam light interference signal 136 for image processing in order to generate the OCT imaging data 146 which is presented on display 152.
In some embodiments of the present invention, such as, for example, that shown in
The OCT scanner housing 208 including the objective lens 210 adds height h2 to the height h1 of the microscope 200 in the embodiment shown in
For example, some embodiments of the optical component design of an OCT scanner adapter 206 may have the optical design which is shown schematically in
It will be appreciated that
Accordingly, by using an optical design for the scanning mirror assembly optics according to embodiments of the present invention, the combined stack height h3=h1+h2 can be made much shorter than was possible with previous optical design configurations.
By reducing the stack height as much as possible, the microscope can be better positioned for surgery. For example, it may be positioned far enough from an in-focus tissue sample to allow access to the tissue sample being operated on by a user yet close enough to conform with typical human physical form factors. In other words, the OCT adapter height h2 is preferably reduced as much as possible to allow conventional operation of the microscope by the user who is also performing the surgical operation, whilst the microscope is optically focused on a focal plane over the tissue sample using the microscope objective lens 210 of the OCT scanner adapter 206 via which the OCT probe beam is emitted onto the tissue sample.
Some embodiments of the OCT scanner adapter 206 microscope accessory shown in
For example, in some embodiments, and as describer later below referring to
Some embodiments of the OCT scanner assembly using the PSD 160 are able to support very high-speed scan rates, for example, 36000 A-scans per second or higher, where an A-scan is a depth scan at a point in the tissue. Each B-scan is formed from multiple adjacent A-scans of which can be used to generate an image with depth information for the area being scanned in the form of a slice through the sample being scanned to show structures at different depths along the slice. In other words, a B-scan provides information about structures in the z-direction or depth direction along a single linear traversal of the tissue sample, for example, a linear scan along a line definable in x-y coordinates such as those shown schematically in
The embodiment of the scanning mirror assembly shown as an optical block 310 in
Some embodiments of the optical design of the scanning mirror assembly specify one or both of a minimum and a maximum exit beam diameters for one or more optical components. For example, the beam diameter of the OCT beam input via the optical fibre 308A when it exits the collimating lens assembly 516, shown as collimating lens 602 in
Another exit beam diameter which is selected for is the beam diameter of the OCT beam 312 that exits from the focusing lens assembly 314 of the OCT scanner adapter 206 which then is incident on the fold mirror 316. The focusing lens 314 expands the OCT scanning or probe beam diameter to 10.6 mm to set the OCT system numerical aperture and ultimately the resolution for the OCT scanner system based on the focal length of the OCT microscope objective lens 210. For the case of the 175 mm working distance (not focal length) objective lens 210, the lateral resolution is 30 μm, in other words, the resolution is better than 33 line pairs per millimetre. This can be contrasted with the 6 micron, 166 line pairs per mm, resolution at the intermediate image plane located at the exit of the OCT objective lens assembly 510, 512.
In some embodiments, the maximum FoV which a user can set for a scan is a 20 mm by 20 mm area using a suitable user interface, for example, a user interface of an apparatus implementing the image processing system 148 shown in
Examples of the embodiments of the present invention which are used for surgical procedures and other use contexts requiring real-time image processing may use a high-dispersion configuration of the OCT system 100 with the OCT scan adapter 206.
The term real-time as used herein, refers to processing delays which are imperceptible, for example, 60 ms or less, and delays of around 30 ms or less are also achievable in some embodiments. The design incorporates a high angle of incidence at the scanning mirror to reduce the compound angle coupling when performing a 2D scan of a sample with both high lateral optical resolution and a telecentric image plane.
The following description of the optical design of the scanning mirror assembly 310 shown in
The scanning mirror assembly 310 includes a moveable reflective surface 334 comprising a micro-electro-mechanical system having a suitably large numerical aperture. The term “large numerical aperture” here refers to a clear aperture of the reflective surface 334 which is preferably greater than about 4 mm in diameter. The term “clear aperture” means the range of angles which can be imaged via the aperture without any supports or clips or other forms of retaining elements getting in the way. The larger the diameter of the clear aperture of the scanning mirror reflective surface 334, the slower the scan rate as the probe beam then covers a larger diameter. Whilst a MEMS mirror with a clear aperture of around 7 mm is already known in the art, even with optical feedback, such known MEMS mirrors with large clear apertures are not capable of scanning at an acceptable rate for real-time imaging applications such as are required for OCT when performing optical surgery. In some embodiments, the scanning mirror has a 5 mm clear aperture. In some embodiments, a 4.2 mm clear aperture diameter scanning mirror assembly is used which enables scans to be performed at a sufficiently high rates for the SD-OCT system shown in
In OCT, the axial and lateral properties are decoupled. Lateral resolution is defined by the objective and focusing media in front of the sample. Axial properties of the interferometry are defined by the coherence properties of the OCT scanning light source and also how, after being returned from the sample, the returned OCT signal is sampled at the detector. The OCT axial resolution is dependent on the spectral bandwidth of the OCT scanning light source and the centre wavelength. Axial imaging depth defines the axial range which is covered in a B-scan. It is also defined by the maximum fringe frequency that can be detected as the maximum frequency of an interference spectrum is what decodes the maximum depth scanned.
An A-scan, is an amplitude depth scan along one-dimension, usually referred to as the z-axis, through a sample, a B-scan is a lateral scan in two-dimensions across a sample formed by a series of A-scans. In other words, for each sample point, the spectrally dependant interferometric fringe pattern created by the back reflection from the reference mirror of the OCT interferometer and the back reflection from the sample is recorded as an A-scan. Multiple A-scans are made to generate other scans such as B-scans which allow a complete depth profile of the sample reflectivity at the beam position to be generated.
In some embodiments, the open aperture diameter is 4.2 mm or above.
In some embodiments, the OCT scanner adapter 206 includes a high speed OCT MEMS based mirror scanning assembly 310 which uses a position sensitive detector system 160 to provide a control loop feedback for controlling the positioning of the OCT beam during the scan. The control loop feedback has a technical benefit in that it allows the OCT scanner to generate more B-scans per second of the object of interest being scanned. In other words, the control feedback loop provided in some embodiments of the present invention allows suppression of ringing behaviour and resonant behaviour caused by a step change in driving voltage at the end of a scan line.
In
An optical port 214 is also provided for OCT scanning light to be input and output from the OCT scanner adapter 206. An optical fibre 308a connected to the optical port 214 feeds in OCT light from the coupler 104 shown in the OCT scanning system 100 of
OCT Light from the OCT light source 102 follows an optical path 101a along the illumination arm 101 to the coupler 104 and then takes optical path 105a along the probe arm 105 in
In some embodiments, the optical fibre connector 308 via which OCT light is input to the MEMS mirror block 310 is a fibre connector to angle polished connector.
The optical block housing the MEMS scanning mirror assembly 310 also houses the optical components of the optical angular displacement mirror position measurement system 156 for the scanning mirror assembly, shown in
The same mirror reflective surface 334 in the scanning mirror assembly housed in optical block 310 reflects both the input OCT beam and a mirror positioning reference beam from a different source (see
The OCT light following the optical path 105a received via OCT data connection fibre 308 is reflected in a different optical plane at the reflective surface 334 to the optical plane at which light from the light source of the angular displacement mirror measurement system 156 is reflected.
The reflected OCT beam then follows an optical path through the OCT scanner adapter 206 from which it emerges via the microscope objective lens 210 to probe the object of interest, for example, a tissue sample such as the in-vivo eye tissue shown schematically in
The OCT light which is reflected, back-scattered or otherwise returned from structures within the tissue sample then follows a return path 105a back through the scanning mirror assembly of the optical block 310 and along optical fibre 308a. The returned OCT light then exits the OCT scanner adapter 206 via optical port 214 and is fed into the OCT system 100 where it is combined and interferes with light returned from reference arm 103 at coupler 104. The resulting interference pattern is detected in the OCT system 100 of
In the example embodiment of the OCT adapter 206 shown in
In
The configuration of the fold mirror 316, the beam splitter 318, and the objective lens assembly 210 of the OCT scanner adapter 206 are collectively designed so that OCT beam is lifted out of the plane it follows through the scanning mirror assembly by only a small amount, in order to be able to exit via objective lens 210. The amount of lift required is affected by the tilt-angles for the beam splitter and the fold mirror and beam entry geometry. The additional height h2 that the OCT scanner adapter 206 adds to the height of the microscope is accordingly also minimised by using this optical design. For example, in some embodiments the OCT scanner adapter housing 302 adds 40 mm or less to the overall height h1 of the microscope housing 202. In some embodiments, the additional height h2 is 36 mm or less. This can be achieved with a lift of, or around, 27 mm in some embodiments using suitable tilt-angles for the beam-splitter and fold mirror.
In some embodiments, and as shown in the example embodiment of
In some embodiments, and as shown in
Also shown schematically in
It will be appreciated that the angle of incidence and the locations of the beam paths shown in the drawings are for illustrative purposes only and not to scale.
The design of the MEMS scanning mirror assembly is configured so that the illuminating mirror positioning light beam 400, shown in
The OCT scanner optical components shown in
In some embodiments, the fold mirror lifts the OCT beam by 27 mm out of the optical plane of the scanning mirror assembly.
The optical design of the 2D scanning mirror assembly is suitable for use in other types of OCT scanners such as OCT scanner 164 in
In other words, the 2D scanning mirror assembly optical design of
Some example embodiments of the micro-electro-mechanical system, MEMS, two-dimensional scanning mirror assembly 310 shown in
The scanning mirror assembly optics also comprises a collimating lens assembly 516 for the light introduced via the connector 308. Collimating lens assembly 516 is configured to output light from the point light source with an exit beam diameter above a threshold exit beam diameter towards the reflective surface suitable for a desired scanning application. After reflection at the reflective surface 334 of the scanning mirror 112, the scanning light beam passes via an objective lens assembly 510, 512 to exit the scanning mirror assembly.
The reflective surface 334 is configured to reflect an incident collimated light beam to form a scanning beam, for example, an OCT probe beam if the point light source provides OCT light, which exits the mirror assembly via an objective lens 510 and field lens 512 (collectively also referred to as the objective lens assembly 510, 512) as a telecentric beam 312 towards a telecentric image plane 154. The optical design of the components in the scanning mirror assembly is configured to ensure the scanning beam is able to perform a scan with a resolution better than a resolution threshold.
The optics of the scanning mirror assembly are configured to provide a total track length, L, for the path from the point light source, for example, from the end-face of the optical fibre or fibre ferrule (see also
The total track length, L, is accordingly kept as short as the optical design layout permits to reduce the lateral and depth footprints X and Y to the smallest possible in some embodiments so that the housing of a scanner comprising the scanning mirror assembly 310 can be similarly provided with a small footprint.
By keeping the lateral footprint X as small as possible, side access to the area being scanned is improved which is particularly beneficial when the scanning mirror assembly 310 is a scanning mirror assembly for an OCT scanner adapter 206 which is a surgical microscope accessory as this may improve access to the area being surgically operated on whilst the microscope it is attached to is in use.
In some embodiments of the scanning mirror assembly, the threshold for the exit beam diameter from the collimating lens 516 is at least 3 mm, and preferably at least 3.1 mm. By having an exit beam diameter of at least 3.1 mm, the scanner benefits from a better lateral resolution than a small exit beam diameter allow
In some embodiments of the scanning mirror assembly, the threshold for the telecentric beam resolution at the telecentric image plane 700 is better than 6 microns. In other words, the scan image can resolve features in the sample being scanned which are smaller than 6 microns.
In some embodiments, the scanning mirror 112 may be moved, for example by a controller 162, The scanning mirror assembly may be configured in some embodiments to move about its optical axis and scan over +/−5 degrees in some embodiments.
In some embodiments of the scanning mirror assembly, the numerical aperture of the optical fibre and the focal length of the collimating lens together determine the a suitable threshold for the exit beam diameter of the collimated beam from the collimating lens to at least 3.1 mm into achieve the designed resolution at the focal plane. The combination of focal lengths of a scanning mirror objective lens and a scanning mirror field lens via which the probe beam exits the mirror assembly determines the total track length, L, which is preferably less than 40 mm or thereabouts.
In some embodiments, for example, where the scanning mirror assembly is being used for OCT purposes, the optical fibre has a numerical aperture of 0.14. The optical fibre which feeds in light to the scanning mirror assembly by acting as a point light source may have another suitable numerical aperture value in other embodiments of the scanning mirror assembly providing the numerical aperture allows sufficient light to be fed into the scanning mirror assembly for another context of use along a single mode optical fibre 308a.
In some embodiments of the scanning mirror assembly, the objective lens 510 comprises a F2.7 Biconvex doublet lens and the field lens 512 comprises a F19 positive/negative meniscus doublet field lens.
In some embodiments of the scanning mirror assembly, the optical path difference, OPD, of the telecentric probe beam output by the scanning mirror assembly has a radius of curvature is greater than 100 mm.
In some embodiments of the scanning mirror assembly, the telecentric beam is telecentric to better than an incident angle of 0.03 degrees at the telecentric image plane.
In some embodiments of the MEMS scanning mirror assembly, the reflective surface 334 of the MEMS scanning mirror comprises a large-aperture gold-coated silicon mirror bonded to an underlying mechanical structure.
The embodiment of the scanning mirror assembly 310 design illustrated schematically in
As mentioned above, however, the scanning mirror assembly 310 shown in
In some embodiments, the mirror assembly 310 may be provided in an OCT scanner adapter 206 which is used as an OCT scanning accessory for a microscope. 200 The microscope may comprise a surgical microscope in some embodiments and the scanning mirror assembly 310 may be used to generate OCT scans of a sample tissue area being surgically operated on at a sufficiently high rate to allow live OCT tomographs to be generated of the sample tissue area whilst the surgical operation is on-going.
In some embodiments, the SD-OCT scanning system shown in
In some embodiments, the scanning mirror assembly 310 is configured so that OCT light returned from the sample along the OCT probe arm 105 has a lateral optical resolution equal or higher than 6 μm, in other words, the resolution is better than 166 line pairs per mm.
In some embodiments, the scanning mirror assembly 310 comprises a MEMS 2-D scanning mirror assembly which includes at least: a moveable MEMS scanning mirror having a reflective surface 334, an optical fibre 308a connected via an optical fibre connector 308 and configured to act as a point light source for an OCT beam illuminating the reflective surface 334, a collimating lens assembly 516 configured to output OCT light from the point light source with an exit beam diameter of at least 3.1 mm towards the reflective surface 334. The reflective surface 334 is configured to reflect both an incident collimated OCT light beam to form an OCT probe beam and a mirror positioning reference beam. The OCT probe exits the mirror assembly as a telecentric beam towards a telecentric image plane with a resolution of at most 6 microns. The optics of the scanning mirror assembly 310 are configured to provide a total track length, L, from a) an end-face of a fibre ferrule providing the point light source inserted in the optical fibre connector to b) the telecentric image plane of less than 40 mm and preferably less than 36 mm in some embodiments. An objective lens assembly 510, 512 is provided in a probe arm of the scanning mirror assembly to focus the telecentric OCT beam via the OCT scanner (microscope) lens 114, 210 in some embodiments.
The scanning mirror assembly 310 has an optical design which includes the reflective surface 334 of the MEMS mirror being configured so that an incident mirror positioning beam is reflected in a separate optical plane to the optical plane in which an incident OCT scanning beam is reflected. In this manner, the scanning mirror assembly may be also used with a mirror positioning system such as an angular tilt mirror positioning system shown schematically in
As mentioned above, some embodiments of the MEMS based scanning mirror assembly shown in
In some embodiments of the MEMS scanning mirror assembly 310, the scanning mirror 112 is mounted on an underlying mechanical structure or support 500 as shown in
In some embodiments, the reflective surface 334 of the MEMS scanning mirror assembly comprises a large-aperture gold-coated silicon mirror bonded to the underlying mechanical structure 500.
The angular displacement measurement system 156 shown in
The angular displacement measurement system 156 is used to determine the angular position of the MEMS, scanning mirror assembly 310 relative to the incident mirror positioning beam 400 as this allows the mirror position for an incident light beam to be determined when performing a scan and adjusted as the scan progresses. The OCT scan (e.g. a B-scan or volumetric scan) is performed by moving the mirror using the controller 164 in accordance with any scan parameters for a particular scan configuration (these can be input by a user and/or automatically determined for a particular type of scan in some embodiments).
The position of the moveable MEMS mirror surface 334 may be controlled in some embodiments using a suitable angular position controller using closed loop control based on the feedback from a position sensitive detector 160 which detects the reflected mirror positioning beam 402.
In some embodiments, the scanning mirror assembly 310 described above with reference to
In some embodiments, the mirror positioning light source illuminates the reflective surface of the mirror assembly for the optical mirror position feedback channel with an angle of incidence, θ, above 62 degrees, preferably 67.5 degrees, from the normal to the plane of the reflective mirror surface 334.
In some embodiments, the OCT light source illuminates the reflective surface of the mirror assembly for the OCT light channel with an angle of incidence, θ, below 28 degrees, preferably 22.5 degrees, from the normal to the plane of the reflective mirror surface 334.
In some embodiments, the minimum usable aperture at the reflective mirror surface is at least 4 mm, which is particularly useful when the mirror assembly is incorporated in OCT scanner apparatus, such as the compact OCT scanner 206 microscope accessory used for surgical applications.
In some embodiments of the present invention, the OCT apparatus may use closed loop feedback for controlling the scanning mirror position in some embodiments. The use of closed loop feedback may be useful in embodiments where a high scan rate is required such as where a live video or other form of image sequence of OCT scans is required. The use of closed loop feedback supports OCT scans being generated at a high-rate with low lag for time-sensitive applications, such as when OCT scans are provided to guide surgical procedures as it allows the mirror to be moved fast enough and precisely enough to achieve high scan rates and/or high scan resolutions (in other words, high OCT image B-scan or volumetric scan resolutions). In some embodiments, however, an open loop control may be provided.
Embodiments of the present invention can address at least some of the design constraints which are present when designing OCT systems for surgical microscopes. For example, one design constraint is that smaller diameter scanning mirror surfaces are better suited to achieving higher scan rates. The numerical aperture relates to resolution. A clear aperture, i.e., mirror diameter, relates to scan size in that the underlying mechanical structure of the MEMS is the same so a small diameter mirror can such as 2 mm diameter can tilt farther before hitting the MEMS base (up to +/−7 degrees) where as large diameter mirrors such as 7.5 mm diameter can only tilt +/−1.5 degrees before hitting the base. This means that whilst a smaller diameter mirrors could be used and scan a larger area, this would be at the cost of resolution.
In some embodiments, the threshold for the exit beam diameter of the OCT light beam is based on a numerical aperture of the optical fibre and the focal length of the collimating lens assembly.
In some embodiments, the two-dimensional scanning mirror assembly is configured to reflect a mirror positioning beam of light (400) incident at the reflective surface (334) in a first optical plane towards a position sensitive detector (160) configured to generate information on an angle of tilt of the scanning mirror reflective surface (334
In some embodiments of the optical angular displacement measurement system 156 of the scanning mirror assembly 310 shown in
The mirror positioning beam 400 may, however, be reflected back or otherwise returned by the PSD 160 towards the reflective surface 334 of the MEMS mirror. This is unwanted as such returned light can contaminate the illuminating positioning beam and/or the input OCT light beam. Other issues with stray light reflectance in the mirror position detector system include the detected spot position being wrong if there is any stray light on the PSD 160, the diode behaviour may change if reflected light enters the diode cavity, and this can cause intensity fluctuations in the position detector beam which the PSD will detect as changes in position.
To prevent returned reflective elements of the positioning beam being reflected by the MEMS mirror assembly 310, some embodiments of the present invention include additional components such as a light trap. The light trap is suitably configured and located suitably to reduce any reflected mirror positioning reference beam light from re-entering the emitter for the mirror positioning beam and/or contaminating the returned probe beam 312 before it reaches the interferometer.
As mentioned above, some embodiments of the MEMS based scanning mirror assembly shown in
The OCT scanning or probe beam reflected by the MEMS mirror surface 334 of the scanning mirror assembly 310 after reflection passes along an optical path through an OCT objective lens 510 and an OCT field lens assembly 512 which outputs the OCT beam as a telecentric beam into free space towards fold mirror 316. As shown in the embodiments of
The fold mirror 316 lifts the OCT scanning (or probe) beam out of the plane of its optical path through the scanning mirror assembly by reflecting the incident OCT scanning or probe beam towards a beam-splitter 318. The beam-splitter reflects the OCT scanning or probe beam out of the OCT scanner adapter 206 microscope objective lens 210 towards a focal plane 154 for scanning a tissue or similar object of interest, which may be an in-vivo tissue sample or in-vitro sample. The beam-splitter 318 also allows the OCT illuminated area being scanned to be viewed via microscope optics housed in the microscope 200.
In some embodiments, and as shown in
As shown in the embodiment of the OCT adapter shown in
The returned OCT light is reflected via the MEMS scanning mirror surface 334 back along the OCT arm 518 of the scanning mirror assembly 310 back towards the coupler of the OCT system 100 shown in
In the scanning mirror assembly 310, the input OCT light beam is input via the optical fibre connector 308 from the end face 532 of optical fibre 308a passes at the optical fibre ferrule 530 (see also
In the return direction, which is disclosed but not shown in
In some embodiments, the OCT scanner is implemented using an OTS (off the shelf) MEMS (microelectromechanical system) in which the MEMS scanning mirror reflective surface 334 is provided by large aperture protected gold coated silicon mirror bonded to the underlying mechanical structure 500 of the optical block 310. The OCT scanner 206 formed by such a design provides a simplified and miniaturized optical system which has the same optical performance as much larger galvanometer scanning mirror type systems known in the art for use in intraoperative OCT systems.
In some embodiments, the optical block design of the OCT MEMS mirror assembly 310 includes a 2D scanning mirror assembly and a complimentary optical angular displacement measurement system 156 for measuring the position of the MEMS mirror system.
The mirror positioning system which measures the angular displacement of the scanning mirror reflective surface 334 comprises a mirror positioning light source 158 and a position sensitive detector, PSD, 160. The PSD may comprises a PSD lens assembly 504 and a neutral density filter 506 as well as the PSD 160. An example of a suitable PSD detector is a Hamamastu S5991 4 mm×4 mm active area position sensitive detector.
In some embodiments, the angular optical displacement measurement system 156 is provided in the same optical block as the MEMS scanning mirror assembly 310. The optical angular displacement measurement system 156 is used in some embodiments to provide closed loop control of the MEMS scanning mirror position. The closed loop control can be provided by measuring the angle of incidence θ using the PSD 160 and providing information indicating the mirror position derived from this to a controller which allows the controller to more accurately control the tilt angle of the scanning mirror reflective surface 334 as a scan is performed.
This closed loop feedback can allow much high B scan rates to be performed. For example, at least 400 B-scans per second can be achieved as a maximum scan rate at full angular deflection in relation to the maximum field of view, FoV using closed loop control for a 4.2 mm diameter clear aperture mirror 112.
In embodiments without closed loop control i.e., open loop scanning, a low pass filter may be used to prevent the MEMS scanning mirror moving device from reaching its natural frequency excitation state where the MEMS scanning mirror moving device may become resonate by uncontrolled oscillation (which in turn can damage the MEMS scanning mirror moving device). In embodiments where open loop scanning is implemented, the maximum scan rate may be approximately 50 B-scans per second which can be contrasted with the rates achievable by closed loop control. With closed loop control in some embodiments, the scan rates which can be achieved using an example embodiment of the MEMs scanning mirror assembly 310 according to the present invention is approximately 400 Hz or higher.
In some embodiments, the optical components of the MEMS scanning mirror assembly 310 are configured collectively provide a predetermined system numerical aperture for a desired system optical resolution through the microscope objective lens 210. In other words, in some embodiments, the MEMS scanning mirror system components are suitably configured to enable the diameter of the collimated OCT beam 312 output along OCT data connection fibre 308 to match a desired minimum system optical resolution after it has passed out through the microscope objective lens 210.
In some embodiments, all air to glass interfaces within the OCT scanner adapter 206 are designed with convex surfaces to minimize any back reflections from the OCT beam as it propagates through the optical system.
A suitable example of an OCT collimator lens 516 which may be used in some embodiments of the present invention is a F3.2 Biconvex doublet lens. Such a lens has a thick crown glass section which reduces the curvature radii of the lens surfaces and consequently improves colour performance. In some example embodiments, the collimator lens has 10 mm focal length with 100 micron depth of focus which allows for good mechanical focal stability. In some embodiments the OCT collimator lens provides an exit beam which has a 3.1 mm diameter collimated beam (exit pupil diameter) with <¼ wave (root mean square, rms) wave front error.
The OCT light is reflected from the reflective surface 334 of the scanning mirror assembly is focused first by the OCT objective lens 510, and then by field lens 512 before emerging as a telecentric beam 312b. A plurality of angle dependant telecentric beams 312b1,2,3 are shown in
The OCT beam 312 deflected from the mirror surface passes, in other words, through an OCT objective lens assembly 510 (which also comprises field lens 512 in some embodiments) designed so that all scan angles of the light 312b which forms the OCT beam 312, which are shown schematically as OCT exit beams 312b1, 312b2, and 312b3 in
In some embodiments, all air to glass interface surfaces such as 514 are convex to eliminate back reflection artefacts in the OCT image. The OCT objective lens assembly illustrated in
The focusing lens assembly 314 acts as an optical interface for the telecentric OCT beam 312b to the microscope objective lens 210. The scanning mirror assembly could in some embodiments be used without a focusing lens assembly 314 but this would require the sample to be placed at the intermediate image plane 700 at which the telecentric OCT beam 312b is focused on when it emerges from the scanning mirror assembly. So in order to use the OCT scanner 206 without the focusing lens assembly the sample would need to be somehow placed at the intermediate image plane 700. As shown in the OCT scanner example embodiment of
In some example embodiments of the OCT scanner adapter 206 used in a microscope for surgery, the focusing lens assembly 314 is fixed and set at the proper back focal length to collimate and expand an incident telecentric OCT beam 312b to have a 10.6 mm collimated beam diameter at exit. As the OCT beam 312 is collimated on exiting the focusing assembly, it will focus at the focal plane of the microscope objective lens 210 as do the microscope optics.
Alternatively, by adjusting the location of the focusing lens assembly 314 relative to the intermediate image plane, the object distance is effectively being adjusted. This results in the focus location of the microscope objective lens 210 being changed accordingly for the OCT scan whereas the focus location remains fixed for the microscope optics.
A benefit of having a focusing lens assembly 314 in some embodiments of the OCT scanner, such as that of the example embodiments illustrated in
Another benefit of embodiments of the OCT scanner 206 which include a focusing lens assembly 314 is that it may be used in some situations even if the microscope optics are setup improperly by a user of the microscope 200, for example, by a surgeon or assistant. For example, if the microscope is non-parfocal, in other words if the oculars of the microscope are set to infinity for users with corrected eyesight via contacts or glasses, the microscope optics focus at the focal plane of the microscope objective lens. If, the microscope oculars are not set to accommodate the refractive error of a microscope user's eyesight, then some users may move the whole microscope, for example using handles 204a,b as shown in
In some embodiments, the OCT objective lens 510 shown in
In some embodiments, and as shown in the example embodiments of
In some embodiments, the total track length L within the scanning mirror assembly optical block is the sum of the length L1 from the end face 530 of the optical fibre 308a at the optical fibre ferrule 532 to the reflective surface 334 of the scanning mirror and L2, the track length on from the surface 334 to the telecentric image plane 700 as shown in
In some embodiments, the optical path difference OPD at the sample being scanned has an OPD curvature greater than 100 mm.
In some embodiments, the OCT scanning or probe beam is telecentric to better than 0.03 degrees incident angle.
In some embodiments, focusing system 314 provides a mechanism for the OCT beam 312 to be adjusted so that the OCT focal plane can be controlled within a ±30 mm range to align with the microscope optical channel focal plane.
In some embodiments, the MEMS OCT scanner has a lateral X-Y profile where X is less than 42 mm and Y is less than 35 mm as
In some embodiments, the scanning mirror assembly further comprises an optical angular displacement measurement system 156 for determining the angle of tilt of the reflective surface relative to incident light comprising at least: a point light source, a collimator lens assembly for collimating light from the point light source to form a collimated mirror position measuring light beam which is incident at the reflective surface; and a position sensitive detector, wherein the reflective surface is configured to reflect the incident collimated light beam in the first optical plane to form a reflected position measuring light beam which travels towards the position sensitive detector.
In some embodiments of the scanning mirror assembly 310 described hereinabove and with reference to
Advantageously, in some embodiments, where the scanning mirror assembly comprises a scanning mirror assembly 310 in OCT scanning apparatus 206, an input beam comprises an OCT probe beam 312 which is reflected through optical components along an OCT probe beam arm of the scanning mirror assembly towards a sample or similar object of interest 116. The scanning mirror assembly 310 is configured to output the OCT probe beam 312 as a telecentric OCT probe beam towards a focal plane 154 at the sample and the optical path length from the optical source 102 of the OCT probe beam to the sample focal image plane 154 is configured to be equivalent to that followed by a reference OCT beam from the same OCT optical source 112 along a reference arm 103 of a connected interferometer OCT system 100 for 2D scanning of the sample area 116.
In some embodiments, the MEMS scanning mirror assembly 310 disclosed herein is provided as an optical block 310 in an OCT scanner adapter 206 for a surgical microscope 200 which forms part of a connected OCT system 100. Such an OCT scanner adapter 206 preferably has at least a lateral footprint X within or equal to the footprint of the surgical microscope housing and preferably has a length or depth footprint also within the footprint of the microscope. The OCT system 100 outputs an interference signal comprising the OCT scan data 146 to the image processor 148 of the OCT system 100. The image processor 148 then processes the interference signal 146, for example, it may perform a signal transform such as a Fourier transform which allows an OCT image showing internal scanned structures within the scanned area to be displayed in an image on a display 152.1 This image can be generated in real-time in some embodiments so as to guide to a surgeon and/or guide other parties on one or more suitable displays 152 in some embodiments.
In some embodiments of the OCT scanner adapter 206, the OCT scanner adapter 206 is configured to be fixed to the undercarriage of a housing of microscope optics of a surgical microscope, wherein the OCT scanner adapter 206 adds less than 40 mm, preferably less than 36 mm, to the stack height of the surgical microscope.
In some embodiments of the OCT scanner adapter 206, the OCT scanner adapter 206 is configured to be fixed to an undercarriage of the microscope optics housing and aligns an objective lens 114, 210 of the OCT scanner adapter 206 with an optical channel of the microscope optics when the lateral footprint of the housing 208 of the OCT scanner adapter 206 sits within the lateral footprint of the housing 202 of the surgical microscope 200.
In this manner, a surgical microscope, for example, a surgical microscope 200 such as that shown in
Some embodiments of the above disclosed micro-electro-mechanical system, MEMS, two-dimensional scanning mirror assembly (310) accordingly comprise a scanning mirror assembly having an optical design comprising a moveable MEMS scanning mirror having a reflective surface 334, a point light source 308a for a light beam, a collimating lens assembly 516 configured to receive light from the light source and output a collimated light beam with an exit beam diameter above a threshold towards the reflective surface 334, and an objective lens assembly 510, 512 via which a collimated light beam reflected from the reflective surface exists the scanning mirror assembly. The reflective surface 334 is configured to reflect an incident collimated light beam to form a probe beam 312 which exits the mirror assembly as a telecentric beam (312) towards a telecentric image plane with a resolution better than a threshold for the telecentric beam resolution. The optics of the scanning mirror assembly are configured to provide a total track length, L, from the point light source to the telecentric image plane (700) less than 40 mm and the scanning mirror assembly may be provided in an optical block which is less than or equal to 41 mm wide, preferably 40.6 mm wide and less than or equal to 35 mm, preferably 34.5 mm long, excluding the optical fibre connector 308 and MEMS support 500 (see X and Y for the block dimensions shown in
The scanning mirror assembly is provided in some embodiments with a system for controlling beam steering which uses a closed loop feedback mechanism to enable high scan rates. In some embodiments, the embodiments of the closed loop feedback system for a scanning mirror are used in a scanning mirror assembly 310 of an OCT system 100. For example, in some embodiments, it may be used in for an OCT scanning mirror assembly provided in an OCT adapter 206 for a microscope such surgical microscope 200 shown in
Some embodiments of the disclosed feedback system comprise a mirror positioning detection system 156 and a controller 162 and form part of the OCT scanner 164 shown in
Achieving such high scan rates can be challenging given the design constraints that OCT adapters for surgical microscopes are subject to.
In
Some embodiments of the present invention accordingly seek to mitigate or obviate some of the above technical problems by providing a beam steering system which uses a MEMS scanning mirror assembly which is illuminated by a scanning mirror position reference beam which is incident in an optical plane off the optical axis of the reflective surface of the mirror with a non-normal angle of incidence. The use of a reference illumination beam which is off-axis and/or which is incident with a non-normal Angle of Incidence (AOI) reduces or eliminates reflections from any secondary reference surfaces and so helps maintain a much better signal to noise ratio than known systems are able to provide.
Some embodiments of a beam steering assembly according to the present invention can be used to provide beam steering for a scanning mirror assembly such as the scanning mirror assembly 310 shown in
The beam steering assembly disclosed herein maintains a very high signal to noise ratio at the PSD 160 of the scanning mirror assembly 310 so as to optimize the performance of an optical feedback scan control system which controls the position of the reflective surface 334 of the MEMS mirror assembly in a way that supports a high A-scan rate.
In order to maintain a very high signal to noise ratio on the PSD 160 scattered or stray light is reduced as much as possible within the optical feedback channel.
Some embodiments of the scanning mirror assembly 310 achieve this by setting the geometric distortion ratio at the reflective surface 334 to roughly 2:1. This allows the optical feedback channel to then be physically offset from the central optical axis, for example, see
In
The collimating lens 503 (see
The light source 158 for the reference beam 400 may be aligned and focused via a plurality, for example, four, fine pitch screws such as those shown in
In
The PSD imaging lens 504 (also referred to herein as the PSD focusing lens 504) sets the spot size for the reference beam at the PSD 160 to above a minimum threshold required for detection at the PSD. The PSD 160 may comprise any suitable type of PSD, for example it may comprise a silicon photodiode PSD in some embodiments. Also shown in
The PSD imaging lens 504 shown in
The neutral density, ND, filter 506 shown positioned adjacent to the PSD retainer ring 1004 in
The collimated reference light beam 400 from the laser diode light source 158, 502 forms a reference beam 402 for determining the scanning mirror tilt position about its optical axis using PSD assembly 160. The reference beam 400 is incident at the reflective surface 334 of the MEMS mirror assembly at an angle which reduces geometric distortion in an upper vertical plane above the optical centre 1116 of the reflective mirror surface 334.
The optical feedback system 1100 illustrated in
In embodiments where the optical feedback system 1100 is used in a scanning mirror assembly for OCT scanning, such as scanning mirror assembly 310 in an OCT adapter 206, the optical center of the mirror along optical axis 1116 is where the OCT scanning or probe beam 312 is incident.
The reflected PSD reference beam 402 follows the optical path 1104 from the reflective mirror surface 334 towards the PSD device 160 via the PSD focusing lens 504 and ND filter 506 in the embodiment illustrated in
In
The configuration of the optical components shown in
In
The reference beam 400 has a sufficiently high angle of incidence relative to the reflective mirror surface to allow separation of the emitted and reflected reference beam 400, 402 from the returned or reflected beam from the PSD, beam 1110. By allowing the reference beam to pass through a focusing PSD lens before it is incident on the detecting surface of the PSD 160, the beam 402 is focused toward the MEMS mirror optical axis 1116 and the resulting reflected beam 1110 has an equal but opposite offset relative to the MEMS mirror optical axis 1116. If the angle of the reference beam light is less than 62 degrees in some embodiments of the feedback system shown in
In other words, the high AOI of beam 400 relative to the MEMS surface 334 creates an increased distortion in the Y direction. As the mirror tilts +/−5 degrees in the horizontal (X) direction the scan length remains unchanged for all AOI values. However, as the AOI increases from the normal position relative to the MEMS mirror surface 334 the resulting scan length in the Y direction from a +/−5 degrees tilt in the vertical direction begins to shorten such that by the time you get to 67.5 degrees AOI the Y scan length is roughly ½ the value of the X scan length. So the higher the AOI the more distortion(shrinkage) in the Y direction, if there is too much shrinkage distortion in the Y direction the input beam 400 can be offset from the optical centre 810 by 1 mm and the 402 beam from the +/−5 degrees tilt will still make it through the PSD lens which is the limiting aperture.
The embodiments of the present invention can use a PSD lens 504 which refracts (focuses) the 402 beam to the PSD surface 1108. The refraction results in the 402 beams hitting the PSD surface at a given AOI and the PSD surface reflects those 402 beams at an equal but opposite angle of exit, AOE. This creates a vertical separation between the mirror positioning reference beam 402 and the reflected beam 1110. If there was no PSD lens 504 provided, a mirror positioning reference beam 402 would, when there is no tilt, in other words a zero degree tilt of the MEMS mirror, be incident at 90 degrees to the detection surface of the PSD. This would result in a direct back reflection from the PSD into the light source, in other words, a back reflection into the laser diode 502.
The data from the position sensitive detector 160 is communicated to a mirror position controller 162, 1700 of a control system described later below with reference to
As shown in the embodiment of
Some embodiments of the scanning mirror assembly 310 which use an optical feedback system comprising the optical components shown in
In some embodiments, the rotational axes of the two dimensional, 2D, scanning mirror assembly 310 are not decoupled. This can be contrasted with prior art galvanometric based scanning mirror constructions which are coupled. As a result, however, a geometric distortion may be introduced due to the resulting compound angle defining a non-linear reflection angle. Such a non-linear reflection angle arises as a result of a linear angle deflection from a 2D mirror for any given angle of incidence. In other words, scanning mirror systems which use a linear mirror tilt result in a parabolic scan trace being generated. The magnitude of the distortion relative to the angle of incidence as is shown in
This geometric distortion shown in
As indicated in
The parabolic function in the y-direction for a tilt angle of −5 degrees at a 67.5 degree angle of incidence can be represented by y=0.02x2+2E−15x+17.6 whereas the parabolic function in the y direction for a tilt angle of +5 degrees can be represented by y=0.008x2+1E−14x−17.6 with vertices symmetric about the origin but of opposite sign and in common with the 22.5 degree angle of incidence as represented by: y=0.003x2+2E−15x+17.6 and y=0.001x2+1E−14x−17.6.
The parabolic function in the x direction for a tilt angle of −5 degrees at a 67.5 degree angle of incidence can be represented by y=0.07x2+9.2x+58.4 whereas the parabolic function in the y direction for a tilt angle of +5 degrees can be represented by y=0.07x2−9.2x+58.4 with vertices symmetric about the origin but of opposite sign but not in common with the 22.5 degree angle of incidence as represented by y=2.3x2+95.4x+940 and y=2.3x2−95.4x+940.
As shown in
By configuring the scanning mirror assembly 310 to have a closed loop feedback system which uses an optical feedback system having the design shown in
Advantageously, embodiments of the present invention have an optical mirror positioning design which reduces any source of scattered or stray light within the optical feedback channel and so may provide improvements over prior art systems.
Some embodiments of the present invention set the geometric distortion ratio, GDR, of the scanning mirror, for example the GDR as shown in
Some embodiments of the micro-electrical mechanical system, MEMS, two-dimensional scanning mirror feedback system 1100 shown in
Embodiments of the feedback system 1100 the angle of incidence, AOI, of the illumination beam 400 incident at the MEMS mirror reflective surface 334 results in the angular geometric distortion of the scanning beam profile being reduced by a factor of 2:1 allowing the illumination beam 400 and any illumination light 1110 returned from the PSD 160 to be spatially separated in different planes at the MEMS mirror.
This allows the reference beam to be detected as a plurality of beams which are detectable as separate beam spots 1108a-i at the PSD 160. The PSD 160 is configured to generate beam spot data for a plurality of different incident beam locations which is then communicated to a controller of the scanning mirror tilt position.
In some embodiments, the beam spot data is used by the controller to implement closed loop control of the scanning mirror position, which allows higher scan rates to be achieved than if open loop control is implemented instead.
In some embodiments, the scanning mirror system is an OCT scanning mirror system.
In some embodiments, the OCT scanning mirror feedback system 1100 is part of a scanning mirror assembly for OCT which includes an optical source for an OCT scanning beam which is incident at the optical centre 1116 of the reflective surface 334 of the scanning mirror assembly 310.
In some embodiments of the feedback system 1100, the illumination beam 400 incident at the reflective surface of the MEMS mirror is in a light plane which is offset by an amount which is equal to the offset of a light plane in which the reflected reference beam 1110 returned from the PSD detector 160 is incident at the reflective surface 334 of the reflective surface 334.
In some embodiments of the feedback system 1100, wherein the geometric distortion ratio of the reflective surface 334 of the scanning mirror assembly 310 is approximately 2:1.
In some embodiments of the feedback system 1100, the reflective surface 334 of an OCT scanning mirror assembly 310 is configured so that an incident OCT scanning beam is incident closer to the optical centre or at the optical centre of the reflective surface 334 whereas the illuminating reference beam 400 used to provide optical feedback on the scanning mirror tilt position is incident at a reflective surface 334 in an optical plane vertically offset from its optical centre. In some embodiments, the reference light beam 400 is also offset from the vertical optical axis 1102 of the reflective surface about which the mirror rotates.
In some embodiments of the feedback system 1100, a neutral density filter 506 is located between the PSD 160 and a focusing lens 504 of the PSD lens assembly.
In some embodiments of the feedback system 1100, low specular reflective optical absorption material is provided along the optical path 1106 followed by light beam 1110 which returns from the PSD 160 back towards the reflective surface 334 of the scanning mirror assembly.
In some embodiments of the feedback system 1100, the system further comprises a spatial filter in the emitter optical path.
In some embodiments, the emitter light source 158 of the feedback system 1100 is a laser diode emitter 502.
In some embodiments, the emitter light source 158 is located vertically above the light trap 1112.
In some embodiments, the feedback system 1100 is included in an optical block of a MEMS scanning mirror assembly 310 of an OCT adapter 206 for a microscope 200, for example, an OCT adapter 310 such as is shown in
In some embodiments, the scanning mirror is a high-speed scanning rate scanning mirror, for example, capable of generating B scans at 400 Hz.
In the embodiment of the scanning mirror position optical feedback system 1100 shown schematically in
The feedback system can be used in variety of different use cases to determine a current position of mirror surface 334 and control how the mirror position changes during scans. Accordingly, in embodiments where the scanning mirror assembly 310 is used in an OCT adapter such as the OCT scanner adapter 206 shown in
As shown in
The PSD 160 shown in
In some embodiments, the mirror position feedback signal is an optical, analog, signal which is transmitted to the controller along an optical fibre link. The signal may then be digitised at the controller 1700. Alternatively, as would be apparent to anyone of ordinary skill in the art, the analog optical feedback signal may be suitably digitised before it reaches the controller 1700, either at an intermediate analog-to-digital converter system apparatus or before it leaves the detector.
In some embodiments where an analog signal is generated by the PSD, this will be sent to the controller circuitry, for example, to a printed circuit board, pcb, assembly of the controller. This circuitry may include an OP Amp and one or more other signal conditioning components such as a dedicated low noise Analog to Digital converter. This allows a better quality of signal to be passed on to the microcontroller chip for a mirror mover mechanism used to control the movement of the scanning mirror reflective surface 334. Such controller circuitry may not fit inside the optical block but it may in some embodiments be housed within the OCT adapter housing 208, for example, it may be provided as a printed circuit board 321 as shown in
In some embodiments the microcontroller chip used to implement the closed loop feedback mechanism receives a signal from PSD and sends this with position request signal, for example, as may be determined by scan configuration parameters, and based on this sends a control signal to a mirror mover mechanism 1708.
For example, a user may select a scan pattern using a user interface for an application which configures OCT scans using the OCT system 100 shown in
By providing a closed loop feedback such as
In some embodiments of the system shown in
In some embodiments, the mirror mover mechanism 1708 is configured to adjust the position of the MEMS mirror reflective surface 334 in at least two dimensions, in other words a closed-loop feedback system for controlling two-dimensional tilt of a MEMS-based scanning mirror assembly 310 is provided in some embodiments.
Depending on the type of detector array that makes up the detection array of the PSD 160 detection surface, the output of the PSD 160 may be an analogue or digital signal. However, in some embodiments, the PSD generates an optical analog feedback signal 1704 and this is transmitted in analogue form and later digitized at the controller 162, 1700.
In some embodiments, the light source 158, for example, a laser diode light source 502, is configured to receive a drive signal, for example, a laser driver signal, 1702 from the controller 164, 1700. The driver signal 1702 is generated by the controller based on information derived from the received feedback signal 1704 and/or the control signal 1710 from the externa scan driver system. The driver signal may be configured to turn the laser on/off and also control the laser diode power so as to not saturate the PSD in some embodiments. In some embodiments, the controller 164, 1700 comprises an external component outside the optical block forming the scanning mirror assembly 310 but located within the scanning apparatus, for example, within the OCT adapter 206. Alternative, in some embodiments, the controller 1700 may be located in a different system for example it may be hosted on the same apparatus as the apparatus hosting the other interferometer components of the SD-OCT system 100 shown in
The maximum scan rate of the mirror is based at least in part on the speed at which the controller receives data from the PSD 160. It is possible to achieve 2D scanning rates for scans comprising multiple a-scans which are stacked to form b-scans in excess of 400 Hz, in other words, more than 400 B-scans per second may be achieved using the closed-loop feedback system 1700 in some embodiments. Achieving such a high scanning rate is possible in some embodiments due to the high signal to noise ratio of the light detected at the PSD 160, which is a result of the separation of the optical plane of the outgoing reference beam 402 when it is reflected at the scanning mirror reflective surface and the optical plane in which the beam returned after detection by the PSD 160 is reflected in at the scanning mirror reflective surface 334.
In some embodiments of the feedback 1100, the system includes the controller 1700. The controller 1700, responsive to the scan position driving signal 1710 from the scan driver, generates generate drive signals (1702, 1706) for the light source (1702) and the mirror moving mechanism (1708) respectively. This allows the controller to position the scanning mirror reflective surface 334 in two dimensions using closed loop control in some embodiments of the feedback system 1100.
In some example embodiments, the scanning mirror system includes an optical feedback mechanism 1110 for a MEMS scanning mirror assembly 310 where the MEMS scanning mirror assembly comprising a reflective surface configured to reflect light from two different light sources, wherein the two different light sources comprise a primary light source comprising a light source for a primary beam which after reflection by the reflective surface forms a scanning beam, and a secondary light source comprising a light source for a secondary light beam which, after reflection by the reflective surface forms a mirror position reference beam, and a position sensitive detector, PSD, configured to detect incident light of the mirror position reference beam, wherein the PDS is configured to cause generation of a mirror position feedback signal indicative of where the mirror position reference beam is incident on the position sensitive detector, and a mirror mover mechanism configured to be controlled by a drive signal derived from the mirror position feedback signal to adjust the position of the MEMS mirror reflective surface to control the direction of the scanning beam.
The scanning mirror reflects emitted mirror positioning light in a different optical plane from any returned mirror positioning light, and reflects light from a scanning light source in another optical plane. In some embodiments, the primary light beam comprises an OCT scanning or probe beam and the primary light source may be a source at the scanning mirror assembly such as the end of an optical fibre which is configured to feed in OCT scanning light to the MEMS scanning mirror assembly from a remote light source such as light source 112 shown in
In some embodiments, the scanning mirror system further comprises a controller 162, 1700 configured to generate the drive signal for controlling a position of the reflective surface 334 of the MEMS scanning mirror assembly 310 responsive to a beam direction input signal and to the mirror position feedback signal derived for a position of the reflective surface 334. The PSD 160 is configured, responsive to detecting the scanning mirror reference beam on its detection surface, to send a mirror position feedback signal to the controller 162, 1700 indicating the location of the scanning mirror reference beam on the detection surface. The controller 162, 1700 uses this feedback signal to generate a drive signal to control a mirror mover mechanism for the scanning mirror. The drive signal from the controller causes the mirror mover mechanism to adjust the position of the MEMS mirror reflective surface 334 in a way which directs the scanning beam to move in accordance with a set of scan parameters.
The beam direction input signal may be provided by a suitable application for configuring a scan which may also use user input parameters to configure an OCT scan. For example, a user may define an area to be scanned with a series of B-scans or to provide a certain resolution.
In some embodiments, the system further comprises a housing 208 having a primary beam entrance 214 for the primary beam which also acts as a primary beam exit for the returned scanning beam. The scanning mirror assembly and the mirror mover mechanism are located in the housing 208. Within the housing 208, the scanning mirror assembly and the mirror mover mechanism may be provided within an optical block such as optical block 310 shown in
In some embodiments, the mirror mover mechanism is configured to adjust a tilt position of the MEMS mirror reflective surface in at least two dimensions.
The mirror position feedback signal may be a digitalised signal based on an analog signal generated at the PSD. The mirror position feedback signal may be digitized at one of the PSD, the controller or at another apparatus configured to perform analogue to digital signal conversion on an analog signal received from the PSD and which outputs the resulting digitized signal as the mirror position feedback signal to the controller.
In some embodiments, the secondary light source is also configured to receive a drive signal from the controller, the drive signal is generated by the controller based on information derived from the received feedback signal. For example, the drive signal from the controller may control the power output of the secondary light source and/or turns it on and off in some embodiments.
In some embodiments, the feedback system may also include the controller 162, 1700 although the controller may be provided remotely in some embodiments. In other words in some embodiments, the scanning mirror system for providing optical feedback using a mirror position system such as the feedback system 1100 shown in
In some embodiments, the secondary light source point of injection into the scanning mirror assembly, the scanning mirror reflective surface, and the PSD are configured such that the secondary light beam is incident at the reflective surface in an optical plane at or slightly offset from the optical centre of the reflective surface. The optical plane of reflection of the scanning light, for example, OCT scanning light in some embodiments, is different from the optical plane in which the mirror position reference light beam 402 is incident at the reflective surface 334 either outwards and different from the optical plane in which a returned reference beam reflected from the PSD is incident at the reflective surface.
In some embodiments, an angle of incidence of the secondary beam incident at the MEMS mirror reflective surface may be less than 67.5 degrees relative to the surface plane of the mirror. This may reduce the angular geometric distortion of the scanning beam profile by a factor of 2:1.
In some embodiments, the reference beam is detected by the PSD as a plurality of beams, and the plurality of beams may be individual detectable as separate beam spots at the PSD. In some embodiments, beam spot data generated by the PSD when it detects a beam spot location of the incident mirror position reference beam is communicated by the PSD to the controller.
In some embodiments of the scanning mirror system, the beam spot data generated by the PSD when it detects a beam spot location of the incident reference beam is communicated by the PSD to the controller, wherein the controller is configured to control a horizontal and vertical tilt position of the reflective surface 334 of the scanning mirror assembly.
In some embodiments, the scanning mirror assembly is part of an OCT scanner system and the primary beam is an OCT scanning beam.
In some embodiments, the mirror position reference beam is focussed by a PSD imaging lens before being detected by the PSD.
In some embodiments, the scanning mirror system further comprises a neutral density filter located between the PSD imaging lens and the PSD.
In some embodiments, the scanning mirror system further comprises low specular reflective optical absorption material along an optical path followed by a portion of the scanning mirror reference beam which is returned back towards the scanning mirror reflective surface.
In some embodiments, the scanning mirror system further comprises a spatial filter in the optical path followed by the secondary beam towards the reflective mirror surface from the secondary light source.
In some embodiments, the light source for the secondary beam is located vertically above a light trap, the light trap being configured to trap light from a portion of the mirror position reference returned from the PSD which is reflected via the MEMS mirror surface 334 back towards the secondary light source.
In some embodiments, the scanning mirror system 1100 comprises an optical block such as optical block 310 shown in
In some embodiments, the scanning mirror system 1100 comprises a MEMS scanning mirror assembly in an OCT adapter for a surgical microscope, and the primary light source is an OCT light source, which, after reflection forms an OCT scanning mirror for scanning tissue areas or samples which are also viewable via the surgical microscope.
In some embodiments, the scanning mirror assembly comprises an optical block configured to function as a MEMS scanning mirror assembly in an OCT adapter for a surgical microscope.
OCT scanners known in the art, for example, the current EnFocus™ scanner by Leica™, are provided as accessories which are under carriage mounted for microscopes. However, such prior art OCT scanner systems have a relatively a large stack height due to the size of the required beam splitter via which OCT scanning light must exit from the scanning mirror arrangement to illuminate a scanned area.
The disclosed embodiments of an OCT scanner adapter 206 which may function as an adapter or accessory for a surgical microscope have an optical arrangement in some embodiments which uses a fold mirror 316 lifts the scanning OCT light beam 312 out of the plane it emerges in as it exits the scanning mirror assembly 310. The beam is lifted towards the beam-splitter 318 which is configured to reflect the light towards the microscope objective lens 210 of the OCT scanner adapter 206.
In some embodiments of the OCT scanner adapter 206, a focusing lens assembly is provided to allow the OCT scanning or probe beam to be focused in an optical plane 154 at a range of depths in the sample tissue being scanned.
In some embodiments of the OCT scanner adapter 206, the focusing lens assembly 314 comprises a focusing lens assembly such as that shown schematically in
As shown in
In some embodiments, the leadscrew is driven via a 15-millimeter geared stepper motor 1806. The total travel of the lens cell housing 1800 is 5 millimetres (+2.5 mm). A travel limit circuit 1814 may be provided in some embodiments to limit the travel of the lens cell housing 1800. The amount of total travel range of the focusing lens elements 1802, 1804 results in a total focal shift of 60 millimetres (+30 mm). The dimensions of the focusing assembly 314 are configured to reduce its height to a level which does not increase the required stack height h2 of the compact OCT scanning adapter 206 above that required to accommodate the scanner optics and the focusing assembly 314 is configured to be small in the optical plane of the scanning mirror assembly to fit between the mounting structure which interfaces to the microscope under carriage which is shown in more detail in
The cross sectional view of the OCT scanner adapter mounting mechanism 2000 shown in
Advantageously, the open base of the recesses 2002a,b,c,d may also, given they will align with the threaded accessory mounting holes of the microscope optics carrier 200, allow microscope accessories to be mounted to the undercarriage of the OCT scanner in some embodiments.
Some embodiments of the present invention comprise a mounting assembly 2000 for an OCT scanner adapter 206 configured for use as a microscope accessory. The mounting assembly 200 comprises at least two mounting blocks, each block comprising a plurality of threaded recesses 2002 arranged to align with corresponding threaded recesses on a housing 202 on the undercarriage of a microscope optics carrier. The threaded recesses 2002a,b,c,d are open at each end and are configured at one end to hold screws 2004 which when extended attach to the microscope accessory carrier housing 202 and at the distal end of are configured to allow another microscope accessory to be attached, to allow the use of the other microscope accessory when the OCT scanner adapter 206 is attached to the microscope carrier optics 200. An example of a microscope accessory which may be attached in this manner is a retinal view lens.
As shown in the beam-splitter arrangement 2300 of
The compound beam splitter arrangement 2300 used in some embodiments of the present invention results in OCT scanning light beam 312 passes through the objective lens 210 off-set from the central optical axis 2302 of the objective lens. As shown in
The compound angle beam splitter arrangement comprises in some embodiments a beam-splitter 318 (see also
The stack height of the OCT scanner adapter 206 is accordingly dependent on the vertical lift and so also dependent on the mirror fold angles and the beam splitter angles. The vertical lift of the OCT scanner adapter 206 is configured to have a value preferably of a least 25 mm. Any further reduction in vertical height comes with a corresponding tilt angle change for both the Fold Mirror and the beamsplitter which may cause issues such as, for a fold mirror tilt angle change, an increase in the overall length of the fold mirror 316. This could encroach on the clear aperture of the microscope objective lens 210 meaning the mirror 316 could be seen by the surgical assistant and also the camera of the microscope which is not desirable. Another issue is caused by a change to the beamsplitter tilt angle. Changing the beamsplitter tilt angle relative to the optical plane of the OCT scanning beam as it emerges from the scanning mirror assembly 310 (and if used, from the focusing assembly 314) causes the angle of incidence for the microscope illumination to become closer to the microscope objective lens normal incidence. This could result in unwanted glare in the surgical view through the microscope optics/camera.
The angle of incidence AOI of the OCT beam at the beam splitter to achieve this degree of lift is 27-degrees relative to the normal of the surface of the beam splitter relative to the central optical axis of the objective lens and 1-degree relative to the OCT optical plane of the scanning mirror assembly 310. The OCT beam angle of incidence at the complementary compound angle fold mirror 316 is 72 degrees relative to the normal of the mirror surface of the fold mirror relative to the central optical axis of the scanning mirror assembly 310 (and if used, of the focusing assembly 314) and 3 degrees relative to the OCT optical plane of the scanning mirror assembly 310. Collectively the compound angle beam splitter arrangement sets the reflected OCT scanning beam 312 to be colinear with the rear optical channel of the microscope optics carrier 200 in embodiments of the OCT scanner adapter 206 which provide a rear entering optical path for the microscope camera.
In some embodiments, a surgical microscope may have as many as four optical channels which may be orthogonal to each other. A surgeon or similar user will face the microscope oculars so that two of these channels provide a surgeons view and two orthogonal channels may be provided for an assistant at 90 degrees to the channels used for the surgeon's view. At the rear of the microscope, taking the front side as the location of the oculars used by the surgeon, a channel is provided for a camera view, and this camera view will also use the microscope objective lens 210 provided by the OCT scanner adapter 206 when this is attached to the microscope 200. This back-channel used by the microscope camera is where the OCT light is folded to by the folding mirror 316 of the OCT scanner adapter offsets from the optical axis of the microscope objective lens 210. In other words, in some embodiments of the OCT scanner adapter, the OCT beam is folded into a camera view channel of the microscope optics. In some embodiments this is a back-channel of microscope. By aligning the OCT beam to the camera channel, parallax issues which might otherwise be associated with using another optical channel of the microscope or the optical axis of the objective lens, may be reduced or eliminated.
The compound angle beam splitter arrangement shown in
Embodiments of the present invention where the folding mirror 316 and beam-splitter 318 fold the OCT scanning light into the camera channel of the microscope optics off the optical centre of the objective lens 210 the OCT light passes through to be focused on the focal plane, however, may require additional calibration of the OCT scan data to ensure meaningful results are obtained. The scanning light 312 which passes through offset from the optical centre of the objective lens 210 is still focused on the focal plane 154 which is flat, however, the phase plane of the OCT light is not flat at the focal plane 154. Any suitable calibration technique can be used to match the phase plane to the focal plane however so that when OCT light 312 which has illuminated sample tissue 116 is returned to the interferometer OCT system 100 shown in
In some embodiments of the OCT Adapter 206, the adapter is an under carriage mounted scanner such as
In some embodiments, the OCT adapter 206 is under carriage mounted with a rear entering optical path offset from the centre of the objective lens by only 1.5 millimetres, reflected to the focal plane via a compound angle beam splitter set at an angle of incidence of 27-degrees by 1-degree, and a complementary compound angle fold mirror set at an angle of incidence of 72-degrees by 3-degrees which sets the reflected beam collinear with the rear optical channel of the microscope optics carrier. One benefit of this includes removing any parallax issues associated with the rear optical channel. Another benefit is that the stack height is reduced to a minimal stack height of 36 millimetres. This is a decrease of 22 millimetres between the EnFocus™ under carriage-mounted scanner system known in the art and the smallest height form factor of an OCT under carriage mounted scanner adapter according to some embodiments of the present invention.
Those of ordinary skill in the art will appreciate that a return light path for the OCT beam is also defined by the optical path taken by the OCT beam and that references to the optical path the OCT beam passes through via optics of the OCT scanner and OCT system to scan a sample or tissue area also relate to the return optical path the OCT light will take back to the coupler 104 shown in the OCT system 100 of
It will also be apparent that whilst OCT system 100 shown in
The example embodiment shown in
Some embodiments of the keratoscope relay mechanism disclosed herein comprise for an LED ring 2700 such as is shown in
In
The keratoscope relay mechanism of OCT scanner adapter 206 is used when the OCT scanner 206 is attached as an accessory to the undercarriage of a microscope 200 used to examine or for surgery on an eye and which has a keratoscope illumination source mounted concentric to where its microscope objective lens is located on its undercarriage. When the OCT scanner adapter is attached to such a microscope however, the original keratoscope illumination source will be obscured.
The original microscope mounted keratoscope light source comprises a series, for example 50, individual LEDs arranged in a circle of slightly larger diameter than the objective lens of the surgical microscope 200 optics. In addition to the ring of LEDs, an adapter ring consisting of a series of light pipes each of which corresponds to an LED element of the Keratoscope illumination may be attached to underside of the microscope optics carrier also concentric to the microscope optics objective lens so as to be able to, for example, illuminate a patient's eye
The function of the light pipe adapter ring is to transfer the direct illumination from the series of LED arranged on the undercarriage of the microscope housing 202 to a location coincident with the objective lens housing thus producing an unobstructed ring of illumination to the surface of the cornea of the patient under surgery. By illuminating a patient's cornea in this way, an indication of the toric orientation of the cornea based on the LED ring shape as imaged through the microscope can be obtained. If the LED ring is imaged as a perfect circle, this indicates no aspheric or toric curvature of the cornea whereas if the LED ring is imaged with an elliptical shape this indicates not only the presence of toric curvature but also the alignment of the curvature axis which is indicated by observing the major axis of the ellipse.
When attached as an accessory to such a microscope 200, the OCT scanner adapter 206 provides a microscope lens 210 which replaces the objective lens of the microscope and obscures the original keratoscope LEDs on the base of the microscope.
Some embodiments of the disclosed OCT scanner adapter 206 are configured with a replica ring of light emitting diodes, LEDs, 2700 arranged about the microscope objective lens 210 such as are shown in
The keratoscope relay mechanism comprises the ring of replica LEDs 2700 embedded into the underside of the OCT scanner adapter housing 208 and the light pipe adapter ring mounting holes 2704a,b which are used to provide keratoscope functionality equivalent to that of the original keratoscope of the microscope.
As shown in
The set of replica LEDS 2700 may comprise the same number and configuration around the objective lens 210 as the number and configuration of the original LEDS arranged around the microscope objective lens of the microscope 200 to which the OCT scanner adapter can be attached as an accessory. In some embodiments each keratoscope LED of the replica ring 2700 on the OCT scanner adapter 206 is identical or near identical to an original microscope keratoscope LED. In other words, each LED may have a matching specification for its optical characteristics such as its luminance and its emission spectra.
Some embodiments of the OCT scanner adapter 206 comprise an LED gasket 3000 and a photodiode flexible circuit, PFC, assembly 3006 such as are shown in
The workflow of a surgical microscope 200 is accordingly not affected by attaching the OCT scanner adapter 206 as an accessory to the surgical microscope. The functionality of the original surgical microscope keratoscope is directly duplicated in the replica keratoscope ring 2700 of the OCT scanner adapter 200. When the surgical microscope keratoscope is engaged, the LED gasket 3000 blocks its light whilst the PFC assembly 3006 activates the replica keratoscope LED ring 2700.
In some embodiments, the detector of the PFC 3006 detects an illumination state of the microscope keratoscope LEDS and exactly matches said illumination state. In this way, the OCT scanner adaptor keratoscope LEDS may be activated in a matching state. Examples of states which can be matched in some embodiments of the OCT scanner adapter 206 in this way include a full illumination state, a fixation illumination state, or an LED off state.
The keratoscope LED gasket assembly 3000 comprises a foam material or similar flexible light impervious material so that a light tight seal against the under carriage of the surgical microscope 200 is formed when the OCT scanner adapter 206 is mounted in place. This prevents illumination from the keratoscope LEDs located in the under carriage of the microscope from being seen by a patient or by users of the microscope.
The keratoscope LED gasket assembly 3000 also comprises strategically placed photodiode detector openings 3004a,b. The photodiode detectors are located underneath the LED gasket 3000 and are used to detect both modes of the Keratoscope function when activated on the microscope 200. The keratoscope modes which can be detected in this way comprise the fixation mode in which only the front most facing LED is illuminated as a target for the patient to look at or fixate on and the Keratoscope mode in which the full ring of LEDs is illuminated.
As shown in
By using two orthogonally located LEDs, the likelihood of any crosstalk or light leakage from the fixation LED to the second LED which should be illuminated in the advent of Keratoscope utilization is reduced and/or eliminated.
In some embodiments, the LED gasket 3000 and the Photodiode Flex Circuit 3006 are fitted with a double-sided pressure sensitive adhesive. The LED Gasket support or mount 3002 may be injection moulded from an ABS/Polycarbonate blended polymer material in some embodiments.
When one or both of the photodiode detectors 3100, 3102 detects light from the primary microscope Keratoscope ring-LED on the microscope, it will activate the secondary ring-LED 2700 in the OCT adapter 206 so that this has the same keratoscope state. Similar circuits are used for both the full ring and the fixation LED photodetectors. The comparator 3208 is used to accommodate for the variability of the coupling of the keratoscope LEDs on the surgical microscope. The digital to analog circuit 3206 is used to set the threshold light intensity for the comparator 3208 which will trigger actuation of the replica ring-LEDs to emulate the microscope keratoscope state. The threshold level is software configurable through the on-board controller 3204 and may be adjusted remotely using the data interface 3202, for example, during installation of the OCT scanner adapter 206 as a microscope accessory if required to ensure a more reliable operation.
Those of ordinary skill in the art will appreciate that a return light path for the OCT beam is also defined by the optical path taken by the OCT beam and that references to the optical path the OCT beam passes through via optics of the OCT scanner and OCT system to scan a sample or tissue area also relate to the return optical path the OCT light will take back to the coupler 104 shown in the OCT system 100 of
The terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including” when used herein specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It will be understood that, although the terms first, second, etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element without departing from the scope of the present disclosure.
Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “vertical” may be used herein to describe a relationship of one element to another element as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element, or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
As used herein the term “and/or” includes any and all combinations of one or more of the associated listed items and may be abbreviated as “/”.
Although some aspects have been described in the context of an apparatus, it is clear that these aspects also represent a description of the corresponding method, where a block or device corresponds to a method step or a feature of a method step. Analogously, aspects described in the context of a method step also represent a description of a corresponding block or item or feature of a corresponding apparatus.
It is to be understood that the present disclosure is not limited to the aspects described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the present disclosure. In the drawings and specification, there have been disclosed aspects for purposes of illustration only and not for purposes of limitation.
While subject matter of the present disclosure has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. Any statement made herein characterizing the invention is also to be considered illustrative or exemplary and not restrictive as the invention is defined by the claims. It will be understood that changes and modifications may be made, by those of ordinary skill in the art, within the scope of the following claims, which may include any combination of features from different embodiments described above.
The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C.
| Number | Date | Country | Kind |
|---|---|---|---|
| 23158510.0 | Feb 2023 | EP | regional |
| 23158559.7 | Feb 2023 | EP | regional |
| 23158561.3 | Feb 2023 | EP | regional |
| 23159969.7 | Mar 2023 | EP | regional |
