Patent Application
20130109975
The present invention relates to a system and method for monitoring light transmission and/or backscattering. In particular, the present invention relates to a surgical or medical device for sampling tissue using light.
Light transmission and/or backscattering, typically in the near-infrared, is a well known technique for monitoring blood and other biological tissue constituents. It allows, for example, the degree of oxygenation of such tissues to be established. This is because haemoglobin and myoglobin have different near-infrared optical absorption spectrum depending on whether they are in an oxygenated or deoxygenated state. The oxygenation state can be determined by shining light on the tissue and observing the transmitted or backscattered light intensity. As another example, the content of cytochrome aa3 oxydase in tissue can be determined in a similar way.
Monitoring oxygenation levels is very useful, for example during surgery, as tissue needs to be interrogated in order to establish whether it is correctly perfused by blood. Other applications include emergency care medicine, for the determination of the oxygenation state of brain tissue; sports medicine and rehabilitative cardiology, for the determination of the oxygenation state of muscle haemodynamics and of capillary contractility; vascular surgery, for the determination of blood vessel elasticity by observation of the response of vascularised tissue to adequate stimuli; catheterised tools, as a navigation aid via the identification of different types of tissues through their optical backscattering and/or transmission properties.
U.S. Pat. No. 5,807,261 describes a tool for non destructive interrogation of tissue. This has a light source and light detector mounted directly on the tool or mounted remotely and guided to the surgical field using fibre optic cables. Various source and detector configurations are described.
According to a first aspect of the present invention, there is provided a device for non-invasive measurement of biological parameters that has an emitter that emits radiation that has a range of wavelengths, wherein features are provided on the emitter, the features having at least one dimension smaller than that of the wavelengths emitted by the emitter, so that light output from the device is determined by the sub-wavelength features. This allows the spectral response of the device to be defined by geometry alone.
The sub-wavelength features on the emitter may have one or more dimensions that are less than or equal to half the central wavelength, i.e. λ/2, of the wavelengths that can be emitted. Typically, the subwavelength features have one or more dimensions in the range 10 nm to 350 nm.
The device may have a detector that detects radiation over a range of wavelengths, wherein features having at least one dimension smaller than the wavelengths that can be detected are provided on the detector, so that the wavelength detected is determined by the sub wavelength features. This allows the spectral response of the device to be defined by geometry alone.
The sub-wavelength features on the detector may have one or more dimensions that are less than or equal to half the central wavelength, i.e. λ/2, of the wavelengths that can be detected. Typically, the subwavelength features have one or more dimensions in the range 10 nm to 350 nm. The sub wavelength features may form part of one or more gratings.
The device of the invention has at least one light emitter and/or at least one detector for detecting light transmitted or backscattered by the tissue, wherein one or more structures with sub-wavelength features is formed on the at least one emitter and/or the at least one detector. The sub wavelength features may form part of one or more gratings.
At least two emitters may be provided. The at least two emitters may be provided on a single substrate, thereby forming a monolithic device. The sub wavelength features on the at least two emitters may be such that the light emitted by them is of different wavelengths. The sub wavelength features may form part of one or more gratings.
At least two detectors may be provided. The at least two detectors may be provided on a single substrate, thereby forming a monolithic device.
At least one emitter and at least one detector may be provided. The at least one emitter and the at least one detector may be provided on a single substrate, thereby forming a monolithic device.
The at least one emitter and the at least one detector may be made of different material. The at least one emitter may be provided on a substrate of a first material and the at least one detector is provided on a substrate of a second material.
The at least one emitter and/or at least one detector may comprise semiconductor material. The semiconductor material may be inorganic.
The at least one emitter and/or at least one detector may comprise emitting or absorbing dyes.
Light from each emitter may be in the infrared region. Light from each emitter may have a bandwidth in the wavelength range of 10-140 nm, preferably 20-100 nm.
The emitter may comprise a light emitting diode.
The device may be implantable in the human or animal body. The device may be coated in a non-degradable bio-compatible material that is transparent at the emitted wavelength. The device may include a transmitter for transmitting signals from the implantable device to a remote receiver.
According to another aspect of the invention, there is provided a surgical or medical device that includes a device according to the first aspect. The surgical/medical device may be an endoscope or a laproscope.
Various aspects of the invention will now be described by way of example only and with reference to the accompanying drawings, of which:
a) is a cross section through a monolithically formed backscattering/transmission device;
b) is a cross section through a subwavelength grating part of the device of
In order to simplify the construction of backscattering and transmission measurement tools, the sources and/or the detectors are assembled directly on the sensing element, and on a single common substrate. This allows single devices of the order of a few mm2 or smaller to be made incorporating multiple sources and/or detectors. This device requires no further assembly of optical components and is easier to integrate into a surgical instrument than systems composed of separate parts, such as individual sources, detectors and optical fibres.
a) and 1(b) show an example of a monolithically integrated device for use in an optical measurement tool. This has two emitters 20 and a single detector 22 fabricated on the same semiconductor substrate. The semiconductor substrate is chosen to operate preferentially around 780 nm wavelength emission and absorption wavelength. As an example, the substrate is made of GaAs and/or composites of GaAs. The emitter comprises a light emitting structure, for example an LED or a resonant cavity LED with a relatively broad emission range, i.e. having a wavelength bandwidth in the range range 10-140 nm, preferably in the range 20-100 nm.
As an alternative to forming the light emitting and/or light detecting structures using semiconductor material on a semiconductor substrate, the emitters and/or detectors may instead be formed by depositing different active and detecting materials on a common substrate. For example, the active and detecting materials may include emitting or absorbing dyes, and/or semiconductor Nanocolloids, like CdS or CdSe.
The areas that are operated as emitters are separated electrically, so they can be driven as electrically independent units using separate contacts, for example top contacts 24 and bottom contact 26. The detector 22 is also electrically driven independently through separate contacts, i.e. top contact 24 and bottom contact 26. The contacts can be formed in any suitable way, for example by plasma evaporation of two or more layers of metal chosen between Ni, Ge, Au, Cr, each with thicknesses between 10 and 300 nm, depending on the substrate properties. The bottom contact 26 may be a shared or common contact.
Each emitter and/or detector is covered by a subwavelength grating 28 in order to modify the emission/detection spectral response. The sub wavelength grating has a periodic structure, for example a series of lines or ridges. Each feature or ridge of the sub-wavelength grating may have one or more dimensions, usually a width, that is less than or equal to half the central wavelength, i.e. λ/2, of the wavelengths that can be emitted or detected by the associated emitter or detector. Typically, the subwavelength features have one or more dimensions in the range 10 nm to 350 nm. The subwavelength gratings are an integral part of the device and determine the wavelength selectivity solely by a geometrical property of the device exhibiting features on the subwavelength size scale. These may be created, for example, by a lithographically created pattern. A typical example is shown in
To form the subwavelength structures, firstly a low refractive index buffer 30 is deposited, with thickness between 0 and 100 μm, the range 100 nm to 500 nm being preferred. The buffer material should not be absorbing at the emission wavelength and its thickness is controlled with nanometric precision (+−10 nm). The buffer material, if polymeric, can be applied, for example, by dissolving it in a solvent, by spinning the solution onto the emitters and/or the detectors, and by evaporating the solvent. Preferred polymers are PMMA, SU8 or Polymide. Other suitable materials, for example, SiO2 or amorphous silicon, could be deposited on the emitters and/or detectors using for example thermal or plasma evaporation or sputtering.
On top of the buffer is deposited a transparent layer that has a higher refractive index 31 than the buffer, see
Different areas of the substrate can be patterned in different ways. Certain areas could be patterned to serve as detectors, others to serve as emitters. The emission area could be shaped in any geometrical shape, with typical surface with dimension between 10 μm2 to several mm2. The total detecting area typically covers a surface in the range from a few 10 μm2 of several mm2.
The device could be coated using a suitably chosen biocompatible material 34 (such as, for example, biocompatible silicone, cyanoacrylate or epoxy resins), as shown in
Optical separation between the single emitters and the detectors is achieved via cuts 36 in the coating material 34 which may be as deep as to reach the substrate and realized together with the electrical separation voids. The cuts, which could be as wide as few um up to several mm, could be left empty or backfilled with suitable material.
In use, the different emitters can be modulated with different frequencies or modulation codes. The different wavelength signals can be identified by the detection circuit and the received data processed accordingly. Any suitable modulation technique can be used.
The sources 54 and detectors 56 are positioned on opposite sides of the grasping tool 51, but facing each other, so that light from the sources 54 is directed towards the detectors 56. Electrical cables 58 connect the sources 54 and detectors 56 to an electronic unit 60, which drives the sources 54 and collect the signals from the detectors 56. In use, tissue 62 is grasped between the faces of the grasping tool 51 and light is emitted from the sources 54, passes through the tissue 62 and into the detectors 56 opposite.
The monolithic device of the present invention is compact, robust and simple. It can be readily incorporated into medical or surgical devices such as endoscopes, laproscopes and implantable devices. It can be used in any optical spectroscopy technique that can benefit from the application of multiple sources to biological tissue, and from the assignment, on one or more detectors, of the signal contribution deriving from each source. For example, the invention could be applied to transmission and/or backscattering spectroscopy, fluorescence spectroscopy, Raman scattering.
A skilled person will appreciate that variations of the disclosed arrangements are possible without departing from the invention. For example, although
The work leading to this invention has received funding from the Commission of the European Communities Information Society and Media Directorate-General Information and Communication Technologies—Seventh Framework Programme, a Collaborative Project entitled “Array of Robots Augmenting the KiNematics of Endoluminal Surgery” (ARAKNES) ([FP7/2007-2013) under grant agreement no 224565.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1005930.1 | Apr 2010 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB2011/000528 | 4/6/2011 | WO | 00 | 1/4/2013 |
