Patent Application
20200043161
The present disclosure relates generally to a system and a method for detecting a material in region of interest and relates specifically, though not exclusively, to a system and method for detection of deposits within the region of interest and using polarization-sensitive optical coherence tomography (“PS OCT”).
Currently, there is no method to pinpoint deposits in the retinal pigment epithelium—Bruch's membrane complex (“BM-RPE” complex). Scanning laser polarimetry (“SLP”) can be used to quantify polarization changes in the retina, in vivo, but since SLP only provides en face two-dimensional (“2D”) image quality, changes cannot be linked to a specific depth.
The present invention provides technological advancement.
In a first aspect of the present invention there is provided a method for detecting a material in a region of interest, comprising:
The method typically also comprises determining a threshold of the property. Determining the threshold of the property may comprise comparing depth images or depth image areas having the property, but which are not associated with the material with depth images or depth image areas having the property, but which are not associated with the material. In this case the depth images may be reference depth images of known regions of interest.
The step of processing the at least one depth image using the pre-determined threshold may comprise comparing the at least one obtained depth image with (a library of) reference depth images to determine if the obtained depth image has a property below or above the pre-threshold.
The step of processing the at least one depth image using the pre-determined threshold may comprise filtering out or discriminating against depth image areas or depth images for which the property is above or below the threshold of the property.
The step of detecting the material in the region of interest may comprise analyzing the processed at least one depth image.
The step of providing at least one depth image may comprise using OCT imaging of the region of interest. The OCT imaging may be PS OCT.
The material may be a deposit.
The step of providing the at least one depth image may be performed in-vivo or ex-vivo. In one example the step of providing the at least one depth image is performed in-vivo and the region of interest is a region of interest of a subject, such as a patient. The region of interest may be a region within an eye of the subject, such as the retinal pigment epithelium of a subject's eye and the deposit may be a deposit within the in the retinal pigment epithelium (such as BM-RPE).
For example, the property may be a local intensity of an area or pixels within the at least one depth image. In one specific example the property is a retardance of electromagnetic waves as detectable with PS OCT (for example, by determining a change in polarization angle relative to a reference).
The OCT imaging may be PS OCT and may use a reference at an interface with a deposit at a location below or above the deposit. In one specific example the deposit is a deposit in the retinal pigment epithelium—Bruch's membrane complex of a subject's eye. An inner or outer segment of a photoreceptor layer may be used as a reference.
The method may be conducted to detect deposits located in a retinal pigment epithelium—Bruch's membrane complex of a subject's eye (such as in the BM-RPE) by detecting associated retardance. Further, the method may be conducted to detect retardance induced by a further deposit that is located below another deposit using at least one reference that is positioned above the at least one the other deposit.
In a second aspect of the present invention there is provided a system for detecting a material in region of interest, the system being configured to:
The system typically is also configured to determine the threshold of the property of associated with the at least one depth image.
In a third aspect of the present invention there is provided a non-transitory computer-accessible medium having stored thereon computer-executable instructions for detecting a material in region of interest, the computer arrangement being configured to perform procedures comprising:
The computer-accessible medium may be configured to utilize inner and outer segments of a photoreceptor layer as a reference to collect the at least one retardance located below a retinal pigment epithelium (such as BM-RPE).
In a fourth aspect of the present invention there is provided a non-transitory computer-accessible medium having stored thereon computer-executable instructions for detecting at least one deposit in at least one subject, wherein, when a computer arrangement executes the instructions, the computer arrangement is configured to perform procedures comprising:
The computer arrangement may be further configured to detect at least one retardance induced by a further deposit that is located below or above the at least one deposit using at least one reference that is positioned above or below the at least one deposit. The computer arrangement may also be configured to utilize inner and outer segments of a photoreceptor layer as a reference to collect the at least one retardance for a region below a retinal pigment epithelium (such as BM-RPE). Further, the computer arrangement may be configured to determine the at least one deposit using at least one light source having a central wavelength. The central wavelength may be about 840 nm. The computer arrangement may be further configured to detect the at least one deposit using a polarization having adaptive optics.
In a fifth aspect of the present invention there is provided a system for detecting at least one deposit in at least one subject, comprising:
In a sixth aspect of the present invention there is provided a method for detecting at least one deposit in at least one subject, comprising:
Features and advantages of the present invention will become apparent from the following description of embodiments thereof, by way of example only, with reference to the accompanying drawings in which:
The reference arm 106 includes in this example a polarizer 122 and a mirror 124. The polarizer 122 is used in combination with the polarization controller 116 to ensure that the power returning to a detector can be the same for each polarization state, at each instant (e.g., even and odd depth scans, obtained with orthogonal input states).
The system 100 also has a sample arm 126 that includes in this example a raster scanning device 128 arranged to scan the retina of a subject.
The system 100 further has a detection arm 130. The detection arm 130 has in this example a polarization-sensitive high-speed spectrometer with a collimator 132, a transmission grating 134, a Wollaston prism 136, a focusing lens system 138 and line-scan camera 140. Detected spectra can be mapped to k-space, can be dispersion compensated, such that they can be Fourier transformed to depth without artifacts.
Step 254 of method 200 identifies retardance data points that are suspect using a “normal data base” with 10 young healthy suspects.
The use of PS-OCT for identifying deposits will now be summarized. Exemplary data was obtained with aPS-OCT system as described above with reference to
The processing begins with k-space mapping and dispersion compensation. The real and imaginary parts of the acquired spectra can be converted into Stokes vectors. In this example each pixel in an image has four Stokes vectors I, Q, U and V. The retardance is calculated with respect to a reference.
The interface between the inner and outer segments of the photoreceptor layer (IS/OS) was used as a reference to avoid contamination of the retardance signal with contributions by the PS-OCT system itself, the cornea, retinal nerve fiber layer, and Henle fiber layer. A goal of the measurement was to quantify the retardance induced by the RPE-BM complex, which is located just below this reference.
The IS/OS reflect well, which provides a strong signal for reliable retardance calculation. The stronger reflections, the more reliable the DPPR calculation becomes. An objective is to detect polarization changes induced by deposits, which can occur in the RPE-BM complex, and it is beneficial to find a reference that can be close to these deposits, without being too close such that some spatial averaging can be applied. A reference that can be, for instance, at the top of the retina would not provide the same information, as birefringence contributions from the RNFL and the Henle fiber layer can contaminate the measurement that can be aimed at deposits in the RPE-BM complex. By using a reference at the top of the RNFL, the fast axis orientation of the RNFL can be used for retardance calculations, which can be different from the fast axis orientation of the tissue between the IS/OS and the RPE-BM complex, which can cause serious artifacts.
The IS/OS is beneficial for this purpose. The top of the RPE can also be used, but, as it is more closely spaced to the bottom of the RPE-BM complex, spatial averaging of Stokes vectors (which can be used to filter out speckle noise scrambling) can affect the retardance signal, as Stokes vectors at the top of the RPE can mix with Stokes vectors originating from the bottom of the RPE.
The IS/OS is in this example automatically segmented with image processing software.
Using the exemplary IS/OS as a reference, the retardance induced with respect to the IS/OS can be calculated. This is performed such that a color-coded image is generated, ranging from about 0° to about 180°, that is at about 0° at the IS/OS (see step 252 in
The bottom of the RPE-BM complex is found by an offset of about 66 μm in the downward direction from the segmented IS/OS. Automatic segmentation also provides the location of the bottom of the RPE-BM complex. The DPPR at this location can be collected and displayed in en face images.
Data was collected on ten young healthy subjects, and made a histogram of the DPPR, which shows the distribution of the number of pixels as a function of DPPR magnitude. This Gaussian-shaped histogram shows the relationship between DPPR and percentiles: the 99th percentile can be at a DPPR of 48.6°; the 99.9th percentile can be at 67.8°. Depending on how strictly the data of patients can be thresholded, a certain cut-off to threshold data can be applied.
Data was also collected on 10 older subjects (aged 54-65). By applying the 99th percentile threshold to these data sets, data points that can be suspect can be identified. The suspect data points is set to magenta (in this example).
These maps can be used to monitor the development of deposits. An increase of DPPR with time shows that the RPE-BM complex can be plagued by deposits, which can lead to AMD. However, at this stage, there may not be an indication that the patient suffers from the disease, which can first manifest itself as drusen.
The exemplary elevated retardance values (e.g. above the 99th percentile threshold of 48.6°) are in this example linked to deposits. For example, data sets obtained from two subjects, taken four and two years apart is shown in
Additionally,
A distribution of the retardation that was recorded in the RPE-BM complex of ten young healthy subjects with spectral-domain PS-OCT at 840 nm is used to threshold data points that can be suspect, to identify areas with deposits in patients with age related macular degeneration or patients who are about to have age related macular degeneration.
As mentioned above, a reference for polarization-sensitive analysis can be located at the automatically segmented interface between the inner and outer segments of the photoreceptor layer (IS/OS); the retardance induced by deposits is recorded at or below the RPE-BM complex, which can either be found by an offset from the IS/OS, or by automatic image segmentation. The reference can alternatively also be located at the top of the RPE (towards the RNFL). A reference higher up in the retina, for example, at the top of the RNFL can also be used as a reference. While it can provide less accurate measurements, it can still provide some signal in the RPE-BM complex. This can benefit from a re-calibration of the data set illustrated in
A spectral-domain system at any other central wavelength than 840 nm can be used (e.g. visible range, or near infra-red range near 1050 nm). Further, a swept-source PS-OCT system at any wavelength can be used. The exemplary system can be utilized with adaptive optics.
As shown in
Further, the exemplary processing arrangement 605 can be provided with or include an input/output arrangement 635, which can include, for example a wired network, a wireless network, the internet, an intranet, a data collection probe, a sensor, etc. As shown in
The foregoing merely illustrates the principles of the disclosure. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will thus be appreciated that those skilled in the art will be able to devise numerous systems, arrangements, and procedures which, although not explicitly shown or described herein, embody the principles of the disclosure and can be thus within the spirit and scope of the disclosure. Various different exemplary embodiments can be used together with one another, as well as interchangeably therewith, as should be understood by those having ordinary skill in the art. In addition, certain terms used in the present disclosure, including the specification, drawings and claims thereof, can be used synonymously in certain instances, including, but not limited to, for example, data and information. It should be understood that, while these words, and/or other words that can be synonymous to one another, can be used synonymously herein, that there can be instances when such words can be intended to not be used synonymously. Further, to the extent that the prior art knowledge has not been explicitly incorporated by reference herein above, it is explicitly incorporated herein in its entirety. All publications referenced are incorporated herein by reference in their entireties.
The following references are hereby incorporated by reference in their entireties:
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| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/AU2018/050129 | 2/16/2018 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62460384 | Feb 2017 | US |
