WO2006130316A2

WO2006130316A2 - Devices and methods for determining depth of a boundary using structured light

Info

Publication number: WO2006130316A2
Application number: PCT/US2006/017913
Authority: WO
Inventors: David Wilber Hattery; Brenda Kay Hattery
Original assignee: Apogee Biodimensions
Priority date: 2005-05-06
Filing date: 2006-05-08
Publication date: 2006-12-07
Also published as: WO2006130316A3

Abstract

Methods and devices to improve measurement of the depth of boundaries of interest, such as a layer in diffuse media, such as biological tissue, using quantitative optical diffuse reflectance spectroscopic imaging using structured light.

Description

DEVICES AND METHODS FOR DETERMINING DEPTH OF A BOUNDARY

USING STRUCTURED LIGHT

FIELD OF THE INVENTION

[0001] The present invention relates to quantitative optical diffuse reflectance spectroscopic imaging. The present invention further relates to the use of incident structured light, and more particularly, provides methods and devices for measuring the depth of a boundary such as thickness of a layer.

BACKGROUND OF THE INVENTION

[0002] The present invention is useful for the measurement of depth of a boundary such as layer thicknesses of a variety of organic and inorganic materials in consumer use, industrial settings, and health-related settings. For example, the present invention maybe used to measure the thickness of epithelial tissue.

[0003] Inflammation has been linked to numerous diseases including auto-immune disorders, diabetes, periodontal disease, cancer, and even heart disease. While a true cause and effect relationship has not been generally shown, recent studies have shown potential mechanisms linking inflammation with cancer. The development of drugs that inhibit inflammation may provide a means for chemopreventive treatment that may have applicability in numerous diseases. Despite such far reaching impact, a non invasive measure of general inflammation does not exist in the clinic. [0004] Inflammation in epithelial and endothelial tissue is generally qualitatively assessed and if quantitative assessment is needed, inflammation is generally quantitatively assessed with a punch biopsy which has associated patient discomfort and morbidity.

[0005] A non-invasive, point-measurement based, diffuse reflectance spectroscopy (DRS) device and method for quantifying oral epithelial tissue layer thickness was developed at the National Institutes of Health (NIH). That approach, which utilizes fiber-based optics, facilitates repeated measurements and allows clinicians to better evaluate and monitor therapeutic effectiveness and patient progress. U.S. Patent No. 6,990,369; and Hattery, D., Hattery, B., Chernomordik, V., Smith, P., Loew, M., Mulshine, J., and Gandjbakhche, A. (2004). "Differential oblique angle spectroscopy of the oral epithelium." Journal of Biomedical Optics, 9(5), 951-960. [0006] Optical methods employing visible light are non-ionizing However, scattering of light in tissue limits the potential resolution. The base of the oral epithelium ranges from a normal depth of approximately 100 microns below the tissue surface to 500 microns or more in highly inflamed tissue. Traditional methods that reject the scattered light in tissue images, such as confocal microscopy, are limited to less than approximately 100 microns depth. At the other extreme, even the largest expected depth of approximately 500 microns in oral epithelial tissue is significantly less than required by statistical methods such as optical tomography. Further, the blurring inherent in optical tomography limits the potential accuracy.

[0007] The present invention provides a superior method and device for measurement of boundary depth including the thickness of layers in diffuse media such as epithelial tissue. As described more fully below, the present invention utilizes structured light to attain very high accuracy and performance. Structured light has traditionally been used to overcome the diffraction limit in geometric optics. The present invention combines structured light with DRS (SDRS) for use in diffuse media to achieve high accuracy and performance.

[0008] The incident light generating and conducting means; and the reemitted light detecting means, digitizing means and data conducting means that may be present in a device of interest in the present invention are not limited to fiber-based optics. The instant invention comprises as well fiber-less devices and means which can have increased performance, reliability, and resolution. Fiber-less devices also benefit from increased ease of manufacture and reduced cost of manufacture. [0009] The present invention can comprise fiber-less optics and may further comprise an illumination means and detection means as well as data logic in one compact module. The fabrication of a single electronic package such as a chip for all three functions can reduce size and cost of manufacture.

[0010] The present invention may be used with the light transmitting and/or reemitted light detecting means in direct contact with the layered media or may be used while not in direct contact but proximal to the layered medium.

[0011] Importantly, the present invention is not limited to determination of biological tissue thickness. The present invention may be used in any diffuse media in which a subsurface boundary exists to ascertain characteristics associated with one or more boundaries therein. SUMMARY OF THE INVENTION

[0012] The present invention is directed to improved measurement of the depth of boundaries of interest, such as a layer in diffuse media, such as biological tissue using quantitative optical diffuse reflectance spectroscopic imaging using structured light. Further, a device is described, along with commensurate methods of obtaining depth of a boundary in a diffuse medium from diffuse reflectance spectroscopic images. [0013] The instant invention comprises a method of, and device for, imaging a diffuse media such as layered biological tissue; the method includes the steps of: 1. shining light on the boundary to be assessed, for example, for depth, wherein the light is shone on the diffuse media in a structured manner and wherein the structured manner may be light shone from at least two different angles of incidence; 2. acquiring a plurality of image datasets of the light reemitted from the diffuse media; 3. for each of the image datasets, transforming the data into a multi-dimensional pattern or "feature"; and 4. from the pattern, resolving the depth of the boundary.

[0014] In this manner, by employing structured light, a 2-dimensional (2D) synthetic interference pattern is generated to resolve the depth of a boundary such as that between two layers, for example, the epithelium and the underlying stroma. [0015] A primary object of the present invention is to improve accuracy of the measurement of depth of boundaries in diffuse media by using the multidimensional nature of dominate features defining depth.

[0016] Another object of the present invention is to employ area images (rather than point measurements) to reveal boundary features.

[0017] Another object of the present invention is to remove the need for the device to be in contact with the media surface.

[0018] Another object of the present invention is to simplify manufacturing and improve device performance by removing the need for the use of fibers for either of light insertion or light collection.

[0019] Another object of the present invention is to build a device in which illumination means, detection means, control circuits, and data transmission and processing can be fabricated together in a very small, efficient and inexpensive package. [0020] There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description may be better understood, and in order that the present contribution to the art may be better appreciated. There are additional features of the invention that will be described below. In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of that example. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of the description and should not be regarded as limiting.

[0021] Other objects and advantages of the present invention will become obvious to the reader and it is intended that these objects and advantages are within the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1. A schematic diagram of one embodiment of the present invention. [0023] Figure 2. An illustration of an SDRS probe. [0024] Figures 3 A and 3B. Section views of an SDRS probe.

[0025] Figure 4. A plan view of a compact module containing the three layers: illuminator, detector, and processor, a faceplate, and an optional lens assembly [0026] Figure 5. Schematic of light path from illuminator in an SDRS probe to virtual source point in tissue.

[0027] Figures 6A-F. Images of synthetic interference pattern generated from two images of a light scattering gel with layers of varying thicknesses. [0028] Figure 7. Interference patterns generated from in vivo data. The top pattern is from healthy non inflamed gingival tissue; the middle pattern is also from health non inflamed gingival tissue; the bottom pattern is generated from an area of gingival tissue known to have experienced prior inflammation in the patient but which was not visibly inflamed at the time of imaging.

[0029] Figure 8. Unshaded areas indicate the portion of the synthetic interference patterns shown in Figures 6A-F that would be visible with the Oral SDRS probe. DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] It is understood that the present invention is not limited to the particular methods and components, etc., described herein, as these may vary without departing from the spirit and scope of the instant invention. It is also to be understood that the terminology used herein is used for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention. It must be noted that as used herein and in the appended claims, the singular forms "a," "an," and "the" include the plural reference unless the context clearly dictates otherwise. Thus, for example, a reference to "an interference pattern" is a reference to one or more interference patterns and includes equivalents thereof known to those skilled in the art and so forth.

[0031] Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this invention belongs. Specific methods, devices, and materials are described, although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention.

[0032] The term "diffuse medium" refers to a material that as light travels therein, the light has a much higher probability of being scattered rather than absorbed. [0033] The term "reemitted" refers to light that has entered a diffuse medium and has experienced various scatterings within the medium without being absorbed and then exits the surface of the medium (where it may be captured on a detector). [0034] The term "boundary" refers to a point in a diffuse medium where the optical properties change.

[0035] The term "optical properties" refer primarily to the light scattering and absorption properties of a medium. Absorption is determined by the presence of chemicals that capture a photon. Light scattering is related to the index of refraction of materials. For a diffuse medium, the scattering is much higher than the absorption resulting in reemitted photons that have many scattering events without being absorbed. For a biological diffuse medium, absorbers include melanin and hemoglobin which act in proportion to their concentration. Scattering is determined by many factors in biological tissue including the amount of structural elements such as collagen (higher in connective tissue), the number and size of cells (which differs between tissue types and within a tissue type cells may spread apart by increased water in the tissue which may be associated with irritants, insults or disease), the number and size of intracellular objects such as organelles and cell nuclei (which can change in number and size with changing cellular activity, possibly associated with irritants, insults or disease). In general it is very difficult to absolutely associate a set of optical properties to a particular tissue type or disease state. A change in optical properties at tissue type boundaries is retained despite changes to absolute optical properties within the layers above and below the boundary.

[0036] The term "wavelength" refers to the wavelength of the illumination photons. The term does not imply any particular bandwidth which may be narrow (such as for a laser), broader (such as for an LED), or even broader for other light sources. In the case of broad bandwidth emission it refers to the center, or dominant wavelength. [0037] The term "structured light" in a diffuse medium refers to light designed to interact (either directly or synthetically in sequential imaging) in such a way as to generate a large-scale feature representing a small scale characteristic of the medium. In the preferred embodiment, the structured light generates "virtual sources" near a boundary of interest within the diffuse medium as presented in FIG. 5. Due to their proximity, these virtual sources interact with the nearby boundary differently than far away sources (which would illuminate the boundary with even, diffuse illumination). The result is an interference pattern that is large in scale and which is therefore preserved during diffusion to the surface of the medium (small scale patterns would be blurred and vanish during the same transit).

[0038] Structured light has been used in microscopy to achieve sub-diffraction limit resolution. Gustafsson, "Surpassing the lateral resolution limit by a factor of two using structured illumination microscopy," J of Microscopy, vol. 198 (Pt 2), 827, 2000. In many cases, resolution is limited by scattering, not by the diffraction limit, for example, in diffuse media. The data from a ID slice have been previously shown to match a theory based on a single-scattering photon transport model. D. Hattery et al., "Measuring Oral Inflammation In Vivo with Diffuse Reflectance Spectroscopy," in "Proc 24^th Ann Int'l Con Eng Med Biol Soc (EMBS)" p. 2243, Proc IEEE, 2002; D. Hattery, B. Hattery et al., "Optical Quantification of Epithelial Layer Thickness as a Measure of Oral Inflammation," in "Proc Lasers Dentistry IX," (Fried & Hennig, eds.) vol. 4950, p. 1, Proc SPIE, 2003. Additional information obtained using structured light to generate a full 2D interference pattern enables more useful depth measurement of objects in diffuse media. The invention method is robust to changes in tissue absorption and selection of appropriate laser wavelengths and selection of angles of light insertion can be used to enhance determination of boundary location. Further, the invention includes a production device using micro-optics allowing illumination means and detection means to be efficiently provided in the same small electronic package to allow the majority, if not all, of the circuits to be provided together in a compact probe.

[0039] Described herein is a device and a method which has as one use, determining the depth of a boundary in a diffuse medium. The device comprises an illumination means for shining structured light at a plurality of wavelengths onto the diffuse medium, a detection means for capturing images, a data acquisition means which digitizes the image into image datasets of reemitted light from the surface of the diffuse medium, and a processor for combining image datasets and determining the boundary depth.

[0040] The method further comprises transforming the image datasets into a quantitative value, which is used in derived relationship or an equation or compared to a standard reference curve describing the relationship between interference pattern, or a metric deduced therefrom, and depth of a boundary in a diffuse medium to derive the boundary depth in the measured medium.

[0041] The preferred embodiment of the invention is to illuminate a diffuse medium with structured light. The structured light can be generated from any of a range of known sources, such as a light emitting diode (LED)₃ a laser diode and so on. The light emitting means can be configured to emit light at a plurality of angles relative to the medium or to a perpendicular to the medium. The light emitting means can comprise a single movable and adjustable source or plural sources to enable using structured light at plural angles.

[0042] The wavelength of the light should be chosen to ensure sufficient signal is detected from the range of depths at which the boundary is expected. For example, in biological tissue, choosing a wavelength near 532 nm will increase the probability that photons penetrating much deeper than the epithelial-stroma boundary will be absorbed which will enhance the signal from that boundary. Longer wavelengths will experience generally lower absorption up to about 2000 nm where water absorption is strong. In other non-biological media, shorter or even longer wavelengths may enhance the signal depending on the absorption characteristics of the medium. Thus, the choice of wavelength is optimized by the user for the medium selected and the quality and quantity of reemitted light detected.

[0043] The geometry of the structured light should be selected to place the virtual sources at distinct depths near the expected boundary. Longer wavelengths scatter less in tissue which will enhance the power of the structured light pattern at greater depths in tissue and therefore should be used for deeper boundaries. For angled structured light, the angular difference in the structured light also determines the size and fidelity of potential depth measurements in the interference pattern, and also drives the required resolution o the detection means.

[0044] Multiple wavelengths may be used to gain the advantages of each wavelength and overcome limitations of other wavelengths. The invention, however, is robust to changes in scattering and absorption greater than a factor of about four from the design objective. An image dataset is acquired of the reemitted light from the surface of the diffuse medium for the different structural illuminations and wavelengths. [0045] The image datasets acquired using the structured light may be used to generate a synthetic interference pattern by available statistical treatments, for example, by performing a point-by-point division of the respective data in two datasets at a given wavelength. The depth of the boundary may be obtained by appropriate statistical treatments and comparisons, for example, by reference to a database, or by extracting a feature with a known relationship to boundary depth. In the general case, the data may be directly compared to analytical results using diffusion theory-based or random-walk theory-based expressions, or by solving the inverse problem.

[0046] In one embodiment, data were collected on layered scattering gels with a non- contact CMOS imaging system with illumination at 633 nm by laser diodes. The structured light was angled approximately 30 degrees and approximately 60 degrees to the perpendicular of the imaging detector. Layer thicknesses varied from approximately 1 mm to approximately 8 mm. The image data was transmitted to a computer via a USB cable where it was processed and stored.

[0047] The processing was done, for example, using custom software in C, Mathematica and Octave. Suitable control samples are assessed and compared to the results of the experimental samples. For example, a first step can be to correct the image data using a dark reference. Next, the dynamic range extension method (see, for example, US Patent Application No. 20050273011) can be used. Next, a pixel-by- pixel division can be performed. That sort of statistical treatment will yield an intermediate feature-space image which clearly will show an interference pattern. Certainly, other means for deriving the interference patterns can be used. Features were identified which were linearly correlated to boundary depth. That sort of analysis provided accurate and reproducible measures of boundary depth. [0048] In one embodiment, data was collected on human oral epithelial tissue with layer thicknesses from approximately 0.1 mm to approximately 0.2 mm. The aluminum probe was placed in contact with the tissue. Lasers emitting at 532 nm and 633 nm were used at angles of about 0 degrees and about 45 degrees to the perpendicular of the faceplate. Three images were captured (two angles and a dark reference) automatically in a computer controlled process. The images were carried from the tip of the probe to a CMOS imager using a high resolution fiber optic bundle. The image data was transmitted to a computer via a USB cable where it was processed.

[0049] Data was processed using the same technique as with the gels. Additionally, the intermediate feature space exhibited distinct patterns that indicated when the contact probe was in poor contact with the tissue. This additional capability further enhanced the robustness of the invention against user errors.

[0050] In one embodiment, the CMOS detector is on the same chip as the laser emitters. The emitted laser light is transported from the periphery of the image sensor by a faceplate with reflective/focusing elements.

[0051] Alternatively, the image dataset is communicated to a remote or external processing means and storage means, including a patient record. The communication means can be as known in the art, for example, a physical cable or connector, an optical fiber, a radio frequency signal, an optical signal and so on. [0052] In one embodiment, the data are uploaded to an external computer via a cable or synchronization type interface.

[0053] In one embodiment, the device contains internal processing means and a display means to show the depth of the boundary or other similar indication in real time (e.g. general terms such as: shallow, deep, good, normal, bad, or tissue healthy, mildly inflamed, inflamed, or see your doctor now). [0054] In one embodiment, the device is cordless and transmits the patient data wirelessly (e.g. radio frequency, or optically) to an external destination such as a patient electronic health record and data storage means.

[0055] In one embodiment, the CMOS detector and laser emitters are on the same chip with an image processor means and classifier means. This "smart sensor" also transmits the depth of the boundary to the user's desired destination, for example, a patient electronic health record.

[0056] A device of interest can be presented in any of a variety of format essentially as a design choice. Hence, for those devices destined for essentially direct contact with a medium, the light emitting means and light detecting means are presented in a manner to enable such to occur without interference from extraneous light. For ease of multiple use, the light emitting and detecting means are abutted on essentially a transparent material. The various mechanical and solid state components comprising a device of interest are housed in a device constructed of suitable materials, such as a metal, a plastic and so on, in a form that enables contact with the medium and ease of use. For those embodiments where the light emitting and detecting means essentially do not come into contact with the medium, but in close proximity to the medium, the distal end of a device of interest or other configuration is made to terminate at a fixed position above the surface of the medium using a positioning means as known in the art. [0057] The following non-limiting examples further illustrate the present invention.

EXAMPLES

Example 1

[0058] FIG. 1 is a schematic diagram of one embodiment of the present invention. The SDRS device comprises four modules: a probe 101; an illumination means, "illuminator" 112; detection means, "detector" 113, and processing means, "processor" 114. As shown in section views presented in FIG. 3A and FIG 3B, in this embodiment, the probe 101 contains a module 107 comprised of 3 layers: a compact module 109 containing illuminator, detector, and processor means, a faceplate 110, and an optional lens assembly 111. Power to and data from module 107 is provided by cable 108. [0059] Figure 2 presents a diagrammatic view of another SDRS device embodiment. The probe 101 includes an optional angled tip 102 which contains the module 109. In this embodiment, the probe can be constructed of hard plastic. The probe may be constructed of plastic, metal, or any material easy to manufacture. The angle of 102 may be constructed to optimize data collection for the particular application. If in an industrial setting, no angle may be required, whereas in vivo use on biological tissue may require an ergonomic angle. The angle of 102 can be fixed as shown or may constructed in other embodiments to be flexible depending upon the material and method of construction. For example, silicon rubber or similar materials can be used to allow flexing of the tip. Figure 2 also presents a handle 103, display 104, and an initiating button 105 that starts the sequence of illuminating the medium, acquiring image datasets, processing the data and display of the boundary thickness. Display 104 is provided for purposes of performing calibration and maintenance functions as well as displaying results without need for external processing means. In the handle 103 are wireless communication means to send data to a computer or patient electronic record. Power and data cables 106 are provided to charge internal battery and optionally use external power and processing. Optionally, the data may be transmitted via contacts during synchronization with an external computer with cable 106. [0060] A plan view of the three layers of module 109 is shown in FIG 4. The module 109 allows a compact electronic package to contain illuminator 112, in this case, laser diode; detector 113 using a CMOS Imaging Region; and processor 114 via smart sensor on-chip logic. The faceplate 110 is transparent and protects the module 109 from damage, hi this embodiment, the faceplate 110 also contains reflectors/focusing elements 115 blocked and cut into it to translate the light to within the imaging region at desired tissue insertion angles such as about 0 degrees and about 45 degrees to perpendicular to the surface of the imaging region 113. Alternatively, the device may be designed with holes through the substrate in the imaging region to direct structured light insertion. The optional lens assembly 111 allows for measurements when the device is not in contact with the diffuse medium.

Example 2

[0061] A non-contact probe invented for non-contact measurements on layered non- biological diffuse media was used on scattering gels. Illumination was performed by two 633 ran laser diodes angled at about 30 degrees and about 60 degrees relative to the perpendicular to the surface of the imaging region. Image data was collected using a 12 bit color CMOS camera with a macro lens assembly. Three exposure bracketed images were taken for each illumination angle, as well as a dark reference. Image acquisition was initiated with a cable release and light sources were switched between acquisitions. The data was downloaded to a computer via a USB cable where it was processed. Processing included extending the dynamic range with the method described in US Patent Application No. 20050273011, registration of images, computation of the intermediate feature space, using pixel by pixel division, which showed the interference pattern as presented in FIG. 6. Images were taken of gels with boundaries at known depths between about 1 mm and about 8 mm. Features were identified which correlated with boundary depth.

Example 3

[0062] A handheld probe for contact measurements on biological tissue. Illumination was provided by laser diodes within Class I accessible emission limits conforming to the regulations outlined in 21 C.F.R. Chapter 1, Subchapter J 1040.10 (Laser Products) and 1040.11 (a) (Medical Laser Products). Two 633 nm and two 532 nm lasers were coupled to 7 ft length 250 μm silica fibers for light delivery to tissue surface at about 0 degrees and about 45 degrees to the faceplate.

[0063] Image detection and capture was performed by a 7 ft length silica fiber bundle with 30,000 10 μm fibers (1 x 3 mm fiber optic silica fused face) with biocompatible polymer faceplate in contact with the tissue surface. The other end of the image conduit was coupled to a 12 bit color CMOS camera using a macro lens assembly. [0064] The illumination fibers and image conduit were contained in a handheld probe machined of aluminum and stainless steel. A plastic (polyethylene) housing protected the silica fiber bundle and illumination fibers between the handheld device housing and the module containing the camera and laser diodes. The camera and laser diodes were computer controlled via a parallel cable and USB cable connected to an external computer. Data acquisition was initiated by a momentary handheld switch. The control software was a combination of C and Bash scripts which activated the laser diodes and captured (three exposure bracketed images per illumination angle and wavelength as well as a dark reference image - up to 15 images per tissue measurement) images to a flash storage device, and subsequently transferred the images from the flash storage device to the computer for processing. The processing software on the computer was a combination of C, Mathematic and Octave programs which corrected the data for coupling efficiencies between the silica fiber bundle and the CMOS detector, extended the dynamic range of the images with the method described in US Patent Application No. 20050273011, computed the intermediate feature space image, using pixel by pixel division, containing the interference pattern for each wavelength as presented in FIG. 7, and located a feature and calculated the boundary depth from the feature location. Alternately, patterns were compared to corrected, known depths as shown in the unshaded areas presented in FIG 8. [0065] Although the invention has been described with reference to the above examples, it will be understood that modifications and variations are encompassed within the spirit and scope of the invention. Accordingly, the invention is limited by the following claims. [0066] All references cited herein, are incorporated herein by reference in entirety.

Claims

What is claimed is:

1. A device for measuring the depth of a boundary comprising: a probe; an illumination means for emitting structured light onto a diffuse medium containing said boundary; a detection means for detecting an image dataset generated by said emitted structured light reemitted from the surface of said diffuse medium; and a processing means for converting said image dataset into an interference pattern and for determining the depth of said boundary based on said interference pattern.

2. The device of claim 1, wherein said processing means comprises a communication means for transmitting data from said probe to an external computing device; and an external computing device that converts said image dataset into an interference pattern and determines the depth of said boundary based on said interference pattern.

3. The device of claim 1, wherein said illumination means emits light at a plurality of angles relative to the perpendicular to the surface of the medium.

4. The device of claim 1, wherein said determined depth of said boundary is communicated to an external device for display or entry into an electronic patient record.

5. The device of claim 1, wherein said determined depth of said boundary is displayed on the device.

6. The device of claim 2, wherein said communication means comprises a wireless means.

7. The device of claim 1, wherein said light is emitted at a plurality of wavelengths.

8. A method for measuring the depth of a boundary comprising: a. directing a first structured light into the diffuse medium containing the boundary; b. detecting a first image dataset generated by said first structured light at the surface of said diffuse medium; and c. determining the depth of said boundary.

9. The method of claim 8, further comprising directing and detecting a second or more structured light.

10. The method of claim 9, wherein said plural datasets are used to obtain an interference pattern.

11. The method of claim 8, wherein said determining step is accomplished by comparing said interference pattern to a database of reference interference patterns, wherein each of said reference interference patterns correlates to a known boundary depth.

12. The method of claim 10, wherein said interference pattern is accomplished by performing a point-by-point division of corresponding data in the image datasets.

13. The method of claim 8, wherein said determining step is accomplished using an analytical relationship.

14. The method of claim 13, wherein said analytical relationship is a diffusion theory based expression.

15. The method of claim 13, wherein said analytical relationship is a random walk theory based expression.

16. The method of claim 8, wherein said determining step is based on a feature extracted from said interference pattern and wherein said feature is compared to a database of reference features, wherein each of said reference features correlates to a known boundary depth.

17. The method of claim 8, wherein said determining step is based on a feature extracted from said interference pattern and wherein said boundary depth is calculated using an empirical relationship.

18. The method of claim 9, wherein said structured light is light directed at different angles relative to the perpendicular to the surface of the medium.

19. The method of claim 8, wherein said structured light is emitted at a plurality of wavelengths.

20. The method of claim 8, wherein said diffuse medium is oral epithelium.