CLIAMS:We Claim:
1. A method for obtaining optical tomography of a biological sample, the method comprising:
a. Irradiating the sample with at least one source of light along a circular path around the sample;
b. Collecting the transmitted light along a circular path from at least two distinct planes with respect to the point of irradiation;
c. Transforming the collected light to a signal specific to the contrast, and location of collection of the light; and
d. Analyzing the signal to obtain a three dimensional tomogram of the sample.
2. The method of claim 1, wherein the source of light is a near infra red source having a wavelength in the range of about 650 nm to 850 nm.
3. The method of claim 1, wherein the source of light is a modulated multiplexed source.
4. The method of claim 1, wherein the source of light is perpendicular to the orientation of the sample.
5. The method of claim 1, wherein the first distinct plane of collection is above the source of light and the second distinct plane of collection is below the source of light.
6. The method of claim 1, wherein the collected light is transformed into an electrical signal.
7. The method of claim 1, wherein the electrical signal is analysed to obtain the tomography.
8. The method of claim 1, wherein the sample has a uniform surface geometry, the sample selected from the list comprising of a tissue, an organ and a body part.
9. A method for detecting an anomaly in a biological sample, the method comprising:
a. Irradiating the sample with at least one source of light along a circular path around the sample;
b. Collecting the transmitted light along a circular path from at least two distinct planes with respect to the point of irradiation;
c. Transforming the collected light to a signal specific to the location of collection of the light;
d. Analyzing the signal to obtain a three dimensional tomogram of the sample; and
e. Detecting the anomaly spatially from the tomogram obtained.
10. The method of claim 9, wherein the anomaly is a morphological anomaly of the sample, further wherein the anomaly is one related to a tissue, an organ or a body part.
11. The method of claim 9, wherein the spatial detection is dependent on the sample geometry.
12. The method of claim 9, wherein the resolution of the detection is a circular anomaly of diameter in the range of about 6 mm to about 8 mm.
13. An apparatus for optical tomography of a biological sample, the apparatus comprising:
a. An irradiation arrangement;
b. A pair of circular collectors mounted at two distinct planes perpendicular to the sample;
c. A plurality of detectors coupled to the collector;
d. An analyser coupled to the detectors; and
e. A display coupled to the analyser.
14. The apparatus of claim 13, wherein the irradiation arrangement comprises of
a. A near infrared source of light;
b. A multiplexer coupled to the source;
c. An optical switch having a plurality of ports coupled to the multiplexer wherein the optical switch is configured for switching the source of light from the port currently irradiated to a subsequent port for irradiation;
d. A circular irradiator having a plurality of irradiation points coupled to the optical switch wherein the irradiation points are positioned on the outer circumference of the circular irradiator; and
e. A plurality of optical fiber connecting the port on the optical switch to the point of irradiation on the circular framework.
15. The optical switch of claim 14, wherein the ports are serially arranged on the switch.
16. The apparatus of claim 13, wherein the angle between any two irradiation points is the range of about 10o to about 40o.
17. The apparatus of claim 13, wherein the circular collectors are mounted co-axially on either side of the circular irradiator.
18. The apparatus of claim 13, wherein the detector is a photo detector.
19. The apparatus of claim 13, wherein the analyzer is coupled to the detector either locally or remotely.
20. The apparatus of claim 13, wherein the analyzer comprises of
a. A conversion engine for transforming intensity and phase data into electrical signal;
b. A rendering engine for constructing a tomography.
,TagSPECI:NEAR INFRARED OPTICAL TOMOGRAPHY

FIELD OF INVENTION
The invention generally relates to the field of Instrumentation and applied physics and particularly to a method and apparatus for near infrared optical tomography of biological specimens for diagnosis.
BACKGROUND
Most medical diagnostic scanner devices use ionizing radiation that is harmful to the tissue under investigation. X-ray tomography and emission tomography systems such as positron emission tomography (PET) and single photon emission tomography (SPET) come under this category. The PET and SPET scanning systems have lot of side effects caused by injection of radio-active isotopes in to the body stream under investigation. The requirement of a low life-time isotope for PET system calls for a small nuclear reactor next door. The magnetic resonance imaging (MRI) is extremely costly on account of the requirement for superconducting magnet and the related liquid helium cooling chambers. The noise generated by the superconducting magnet and the related planar switching makes a patient quite uncomfortable. The ultrasound scanning system has inherent drawbacks namely low contrast.
The optical methods for detection and identification of a tumor in soft tissue such as breast tumor are desirable because of its inherent advantages. The probe used, NIR light is non-ionizing and are not harmful since the power requirement of the light beam is within the permissible limits set by medical committees. The system is cost effective, and the recurring running cost is negligibly small compared to maintaining a superconducting magnet or a radio-active reactor. The image resolution and contrast are comparable to those generated by X-ray tomography system and MRI.
One major difficulty to use light probe for a diagnostic tool is the inherent property of human tissue. The human tissue is composed of various constituents such as water, fat, oxygenated hemoglobin, de-oxygenated hemoglobin, lipids and so on. The aforementioned constituents have different absorption and scattering properties. In effect, the tissue media is highly scattering and turbid, which causes light to travel many fold resulting from multiple scattering events inside the tissue during the light traversal through the medium. The light traversal through a tissue, because of multiple scattering, is a mathematically complex problem to solve. The software tools that extract useful information from the measurements made non-invasively from the system are very complex. The measurements are the light intensities of the emerging light coming out of the tissue boundaries. The problem equations are discretized and solved using finite element methods (FEM) that gives a reconstruction and identification of the embedded heterogeneities inside the media.

BRIEF DESCRIPTION OF DRAWINGS
So that the manner in which the recited features of the invention can be understood in detail, some of the embodiments are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
FIG.1 shows a perspective view of the apparatus for near infrared optical tomography, according to an embodiment of an invention.
FIG.2 shows an assembly of circular collectors and circular irradiator of the apparatus, according to an embodiment of an invention.
FIG.3 shows a block diagram of the near infrared optical tomography apparatus, according to an embodiment of an invention.
FIG.4 shows a representative tomograph for a phantom with one inhomogeneity, according to an embodiment of an invention.
FIG.5 shows a representative tomograph for a phantom with two inhomogeneities, according to an embodiment of an invention.
FIG.6 shows a representative tomograph for a phantom with three inhomogeneities, according to an embodiment of an invention.

SUMMARY OF THE INVENTION
One aspect of the invention provides a method for obtaining optical tomography of a biological sample. The method includes irradiating the sample with at least one source of light along a circular path around the sample; collecting the transmitted light along a circular path from at least two distinct planes with respect to the point of irradiation; transforming the collected light to a signal specific to the location of collection of the light; and analyzing the signal to obtain a three dimensional tomogram of the sample.
Another aspect of the invention provides a method for detecting an anomaly in a biological sample. The method includes irradiating the sample with at least one source of light along a circular path around the sample; collecting the transmitted light along a circular path from at least two distinct planes with respect to the point of irradiation; transforming the collected light to a signal specific to the location of collection of the light; analyzing the signal to obtain a three dimensional tomogram of the sample; and detecting the anomaly spatially from the tomogram obtained.
Yet another aspect of the invention provides an apparatus for optical tomography of a biological sample. The apparatus includes an irradiation arrangement; a pair of circular collectors mounted at two distinct planes perpendicular to the sample; a plurality of detectors coupled to the collector; an analyser coupled to the detector; and a display coupled to the analyser.

DETAILED DESCRIPTION OF THE INVENTION
Various embodiments of the invention provide a method and an apparatus for near infrared optical tomography.
One embodiment of the invention provides a method for obtaining optical tomography of a biological sample. The method includes irradiating the sample with at least one source of light along a circular path around the sample. The sample has a uniform surface geometry. The sample is selected from a list comprising of a tissue, an organ and a body part. The source of light is a near infra red source having a wavelength in the range of about 650 nm to 850 nm. The source of light is a modulated multiplexed source. Further, the source of light is perpendicular to the orientation of the sample. Subsequent to the irradiation, the transmitted light is collected along a circular path. The collection of the transmitted light is from at least two distinct planes with respect to the point of irradiation. In one example of the invention, the first distinct plane of collection is above the source of light and the second distinct plane of collection is below the source of light. The collected light is transformed to an electrical signal. The signal obtained is specific to the contrast, and location of collection of the light. The signal is analyzed to obtain the tomography of the sample. The tomography obtained enables contrast and localization of an anomaly embedded within the sample.
FIG.1 shows a perspective view of the apparatus for near infrared optical tomography, according to an embodiment of an invention. The apparatus includes an irradiation arrangement. A pair of circular collectors 2 is mounted at two distinct planes perpendicular to the sample 1. A plurality of detectors 3 is coupled to the collector 2. An analyzer (Not Shown) is coupled to the detector and a display (Not Shown) is coupled to the analyser. Each of these parts shall be described in detail herein below.
The irradiation arrangement includes a near infrared source of light 4. A multiplexer 5 is coupled to the source of light 4. An optical switch 6 having a plurality of ports is coupled to the multiplexer 5. The optical switch 6 is configured for switching the source of light 4 from the port currently irradiated to a subsequent port for irradiation. In one example of the invention, the means for switching between ports is achieved by a stepper motor 7. The ports on the optical switch 6 are serially arranged. A circular irradiator 8 having a plurality of irradiation points 8a is coupled to the optical switch 6. A plurality of optical fibers 9 is employed for connecting the port on the optical switch 6 to the point of irradiation 8a on the circular irradiator 8. The irradiation points 8a are positioned on the inner circumference of the circular irradiator 8. The angle between any two irradiation points 8a is the range of about 10o to about 40o. In one example of the invention the angle is about 30o. The circular collectors 2 are mounted co-axial to the circular irradiator 8. Preferably, the circular irradiator 8 is sandwiched between the circular collectors 2. The transmitted light collected by each of the circular collector 2a is then captured by a plurality of detectors 3. Each collector point 2a is coupled to a specific detector 3a through an optical fiber 10. The output from each of the detector 3 is then sent to the analyzer. The analyzer is coupled to the detector either locally or remotely.
FIG.2 shows an assembly of the circular collectors 2 and the circular irradiator 8 of the apparatus, according to an embodiment of an invention. A pair of circular collectors 2 is mounted at two distinct planes perpendicular to the sample 1. The circular collectors 2 are mounted co-axial to the circular irradiator 8. Preferably, the circular irradiator 8 is sandwiched between the circular collectors 2. The transmitted light collected by each of the circular collector 2 is then captured by a plurality of detectors. One example of the detector 3 is a photo detector. Examples of photo detector include but are not limited to a photodiode, a photomultiplier and the like.
FIG.3 shows a block diagram of the near infrared optical tomography apparatus, according to an embodiment of an invention. The apparatus includes a near infrared source of light 4 and an optical switch 6. The optical switch 6 includes a multiplexer and a demultiplexer, which are controlled using stepper motors 7. The multiplexer takes four fiber inputs from the source of light and provides the multiplexed light on a single fiber. The demultiplexer then takes the single fiber input carrying the multiplexed light and sends the light to circular irradiator 8. The circular irradiator 8 is sandwiched between the circular collectors 2. The reflected light from the circular irradiator 8 is collected by the circular collector 2, which in turn is captured by the detector 3 through the optical fiber 10. The output from the detector 3 is then sent to the analyzer 11.
The analyzer 11 is coupled to the detector either locally or remotely.
The analyzer 11 includes a conversion engine for transforming intensity and phase measurements into electrical signals. The conversion engine is provided with an amplifier to amplify the intensity and phase data. The amplified intensity and phase data are then converted into electrical signals. The electrical signals are sent to the rendering engine for further analysis. The rendering engine is communicatively coupled to the conversion engine. The rendering engine takes the output from the conversion engine for constructing a tomography. It waits for the measurement data, runs the reconstruction algorithm and generates 3-D images. The 3-D volume so reconstructed can be presented as horizontal slices or vertical slices. The user can specify the modes of presentation.
The invention also provides a method for detecting an anomaly in a biological sample. The method includes irradiating the sample with at least one source of light along a circular path around the sample. The transmitted light is collected along a circular path from at least two distinct planes with respect to the point of irradiation. The collected light is transformed to a signal specific to the location of collection of the light. The signal is then analyzed to obtain a three dimensional tomogram of the sample. Finally, the anomaly is spatially detected from the tomography obtained. The spatial detection is dependent on the sample geometry. The resolution of the detection is a circular anomaly in the range of about 6 mm to about 8 mm diameter. The anomaly is a morphological anomaly of the sample. Examples of sample include but are not limited to a tissue, an organ and a body part.
FIGs 4-6 generally show the detection of an anomaly in a sample, according to an embodiment of the invention. FIG.4 shows a representative tomograph for a phantom with one inhomogeneity, according to an embodiment of an invention. The inhomogeneity is created by drilling a cylindrical hole of diameter 7 mm to a certain depth in a phantom that represents a tissue. The hole is filled with a scattering and absorbing media to mimic the anomaly. The phantom is then placed within the circular irradiator and the circular collectors are positioned around the phantom in a manner as described herein above. The light from the source is irradiated in a manner already described herein. The transmitted light from the phantom containing the anomaly introduced is collected by the collectors and sent to the detectors. The detectors convert the light received in to electric signals and send the data to the lock-in amplifier that measures the amplitude and phase of the electric signals. The signals so collected are then sent to the analyser for obtaining the tomography of the phantom with the anomaly. The tomography obtained reveals the contrast in terms of absorption and scattering coefficient, spatial location of the anomaly with respect to distance from the periphery of the sample along with the depth of the anomaly.
FIG.5 shows a representative tomograph for a phantom with two inhomogeneities, according to an embodiment of an invention. The inhomogeneity is created by drilling two cylindrical holes of diameters 6 mm and 7 mm to a certain depth in a phantom that represents a tissue. Each of the holes is filled with a scattering and absorbing media to mimic the anomaly. The size and contrast of each of the inhomogeneity can be identical or distinct. The experiment is carried in a manner as described hereinabove. The tomography obtained reveals the contrast (absorption and scattering coefficient), spatial location of the anomaly with respect to distance from the periphery of the sample along with the depth of the anomaly.
FIG.6 shows a representative tomograph for a phantom with three inhomogeneities, according to an embodiment of an invention. The inhomogeneity is created by drilling three cylindrical holes of diameter 8 mm, 7 mm and 6 mm to a certain depth in a phantom that represents a tissue. Each of the holes is filled with a scattering and absorbing media to mimic the anomaly. The size and contrast of the anamoly can be identical or distinct. The experiment is carried in a manner as described hereinabove. The tomography obtained reveals the contrast, spatial location of the anomaly with respect to distance from the periphery of the sample along with the depth of the anomaly.
The invention as described herein through the specification along with claims appended herein and as illustrated in the drawings provides a method and an apparatus for near infrared optical tomography. The method described herein is a non-invasive method wherein the risk of being exposed to hazardous radiation, as is prevalent in other known methods of tomography, is eliminated. The method as described herein facilitates detection of anomalies which are situated deep within the organ being examined. The method also facilitates resolving the anomaly spatially. The nature and extent of the resolution can be defined by the user.
The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.