Optical computer tomographic apparatus and image reconstruction method using optical computer tomography

• US 5,835,617 A
• Filed: 01/17/1997
• Issued: 11/10/1998
• Est. Priority Date: 01/18/1996
• Status: Expired due to Term

• Current Assignee: Hamamatsu Photonics KK
• Original Assignee: Hamamatsu Photonics KK
• Inventors: Ueda, Yukio, Ohta, Kazuyoshi
• Primary Examiner(s): Couso, Jose L.
• Assistant Examiner(s): Dang, Duy M.
• Application Number:
  US08/785,225
• Time in Patent Office: 662 Days
• Field of Search: 382/131, 382/128, 382/130, 382/154, 382/282, 382/284, 378/901, 378/4, 378/21, 378/74, 378/86, 378/87, 378/89, 364/751, 364/736.01, 364/468.25, 356/379, 356/377, 356/325
• US Class Current: 382/131
• CPC Class Codes: G06T 11/006 Inverse problem, transformation from projection-space into object-space, e.g. transform methods, back-projection, algebraic methods
• CPC Class Codes: G06T 2211/428 Real-time
• CPC Class Codes: Y10S 378/901 Computer tomography program or processor

Abstract

An arithmetic control mechanism of the present optical CT apparatus calculates first light densities in output portions of an object on the basis of a numerical analysis method, when it is assumed that the object is divided into fine segments and all segments have the same value as an absorption coefficient under predetermined conditions equivalent to an actual measurements; and calculates second light densities in the output portions on the basis of the method, when it is assumed that sequentially selected one of the segments has a specific value as an absorption coefficient under the predetermined conditions. Further, the mechanism calculates, as influences of the segments, ratios of the first to the second light densities, thereby obtaining an influence matrix corresponding to an arrangement of the segments; calculates relative ratios of the third light densities in the output portions on the basis of the actual measurements to the fitst light densities, thereby obtaining a relative ratio matrix corresponding to arrangements of input and output portions of the object; and performs a matrix calculation by using the influence matrix and the relative ratio matrix, thereby obtaining feature data of the segments for reconstructing a tomographic image of the object.

Claims

1. An optical computer tomographic apparatus comprising:

a light-projecting unit for individually exclusively projecting measurement light onto a plurality of different first portions of an object to be examined;

a light-receiving unit for individually exclusively receiving the measurement light emitted from said light-projecting unit and transmitted through the object in a plurality of different second portions of the object; and

an arithmetic control mechanism for controlling operations of said light-projecting unit and said light-receiving unit, thereby reconstructing a tomographic image of the object on the basis of a scattering absorption state of the measurement light entering the object,

wherein said arithmetic control mechanism comprises

a first arithmetic unit for calculating light densities of the measurement light obtained in the plurality of second portions on the basis of a numerical analysis method which approximates a predetermined light diffusion equation, when it is assumed that the object is divided into a plurality of fine segments as an aggregate model and all the plurality of segments have the same value as an absorption coefficient under conditions equivalent to the conditions by which the object is measured by using said light-projecting unit and said light-receiving unit,

a second arithmetic unit for calculating light densities of the measurement light obtained in the plurality of second portions on the basis of the numerical analysis method, when it is assumed that only one segment sequentially selected from the plurality of segments has a specific value as an absorption coefficient under the conditions equivalent to the conditions by which the object is measured by using said light-projecting unit and said light-receiving unit,

a third arithmetic unit for calculating, as influences of the plurality of segments, ratios of the light densities of the plurality of second portions calculated by said first arithmetic unit to the light densities of the plurality of second portions calculated by said second arithmetic unit, thereby obtaining an influence matrix corresponding to an arrangement of the plurality of segments,

a fourth arithmetic unit for calculating relative ratios of the light densities of the measurement light obtained in the plurality of second portions on the basis of the actual measurements done by using said light-projecting unit and said light-receiving unit to the light densities in the plurality of second portions calculated by said first arithmetic unit, thereby obtaining a relative ratio matrix corresponding to arrangements of the pluralities of first and second portions, and

a fifth arithmetic unit for performing a matrix calculation by using the influence matrix obtained by said third arithmetic unit and the relative ratio matrix obtained by said fourth arithmetic unit, thereby obtaining feature data of the plurality of segments.

2. An apparatus according to claim 1, wherein the numerical analysis method is a difference method which solves the light diffusion equation by approximating the equation to a difference equation, and the segments are volume elements arranged at equal intervals in the object on the basis of a predetermined coordinate system.

3. An apparatus according to claim 1, wherein the numerical analysis method is a finite element method which solves the light diffusion equation by approximating the equation to a finite element equation, and the segments are finite elements which are a finite number of elements freely separately arranged in the object.

4. An apparatus according to claim 1, wherein the numerical analysis method is a finite volume method which solves the light diffusion equation by approximating the equation to a finite volume equation, and the segments are finite volumes which are a finite number of volumes freely separately arranged in the object.

5. An apparatus according to claim 1, wherein when it is assumed that each of the absorption coefficients of the segments is zero, said first arithmetic unit calculates the light densities of the plurality of segments on the basis of the numerical analysis method.

6. An apparatus according to claim 1, wherein said fifth arithmetic unit obtains a distribution of absorption coefficients in the object as the feature data of the plurality of segments.

7. An apparatus according to claim 1, wherein said light-projecting unit emits continuous light as the measurement light to be projected onto the object, and said light-receiving unit continuously detects the exit measurement light from the object.

8. An apparatus according to claim 1, wherein said light-projecting unit emits pulse light as the measurement light to be projected onto the object, and said light-receiving unit detects the exit measurement light from the object by a predetermined time-resolved measurement.

9. An apparatus according to claim 1, wherein said light-projecting unit comprises a light source for generating the measurement light, a plurality of optical fibers for projecting the measurement light emitted from said light source onto the object, and an optical switch which connects said light source and said plurality of optical fibers by using light branch paths and selectively opens only one of a plurality of output terminals constituting said light branch paths.

10. An apparatus according to claim 1, wherein said light-receiving unit comprises a plurality of optical fibers for extracting the measurement light from the object, a photoelectric conversion device for photoelectrically converting the incident measurement light from said plurality of optical fibers, and an optical switch which connects said plurality of optical fibers and said photoelectric conversion device by using light branch paths and selectively opens only one of a plurality of input terminals constituting said light branch paths.

11. An apparatus according to claim 1, wherein said arithmetic control mechanism further comprises a storage unit for storing various data detected by said light-receiving unit and various data calculated by said first to fifth arithmetic units, and a controller for sequentially controlling operations of said light-projecting unit, said light-receiving unit, and said first to fifth arithmetic units.

12. An apparatus according to claim 1, further comprising a display for processing input image data from said arithmetic control mechanism and displaying a tomographic image of the object.

13. An image reconstruction method using optical computer tomography, comprising:

the first step of controlling operations of a light-projecting unit and a light-receiving unit by using an arithmetic control mechanism, thereby causing said light-projecting unit to individually exclusively project measurement light onto a plurality of different first portions of an object to be examined and said light-receiving unit to individually exclusively receive the measurement light emitted from said light-projecting unit and transmitted through the object in a plurality of different second portions of the object;

the second step of causing said arithmetic control mechanism to calculate light densities of the measurement light obtained in the plurality of second portions on the basis of a numerical analysis method which approximates a predetermined light diffusion equation, when it is assumed that the object is divided into a plurality of fine segments as an aggregate model and all the plurality of segments have the same value as an absorption coefficient under conditions equivalent to the conditions by which the object is measured by using said light-projecting unit and said light-receiving unit;

the third step of causing said arithmetic control mechanism to calculate light densities of the measurement light obtained in the plurality of second portions on the basis of the numerical analysis method, when it is assumed that only one segment sequentially selected from the plurality of segments has a specific value as an absorption coefficient under the conditions equivalent to the conditions by which the object is measured by using said light-projecting unit and said light-receiving unit;

the fourth step of causing said arithmetic control mechanism to calculate, as influences of the plurality of segments, ratios of the light densities of the plurality of second portions calculated in the second step to the light densities of the second portions calculated in the third step, thereby obtaining an influence matrix corresponding to an arrangement of the plurality of segments;

the fifth step of causing said arithmetic control mechanism to calculate relative ratios of the light densities of the measurement light obtained in the plurality of second portions in the first step to the light densities in the plurality of second portions calculated in the second step, thereby obtaining a relative ratio matrix corresponding to arrangements of the pluralities of first and second portions; and

the sixth step of causing said arithmetic control mechanism to perform a matrix calculation by using the influence matrix obtained in the fourth step and the relative ratio matrix obtained in the fifth step, thereby obtaining feature data of the plurality of segments in order to reconstruct a tomographic image of the object on the basis of a scattering absorption state of the measurement light entering the object.

14. A method according to claim 13, wherein the second to sixth steps comprise using as the numerical analysis method a difference method which solves the light diffusion equation by approximating the equation to a difference equation, and using as the segments volume elements arranged at equal intervals in the object on the basis of a predetermined coordinate system.

15. A method according to claim 13, wherein the second to sixth steps comprise using as the numerical analysis method a finite element method which solves the light diffusion equation by approximating the equation to a finite element equation, and using as the segments finite elements which are a finite number of elements freely separately arranged in the object.

16. A method according to claim 13, wherein the second to sixth steps comprise using as the numerical analysis method a finite volume method which solves the light diffusion equation by approximating the equation to a finite volume equation, and using as the segments finite volumes which are a finite number of volumes freely separately arranged in the object.

17. A method according to claim 13, wherein when it is assumed that each of the absorption coefficients of the plurality of segments is zero, the second step comprises calculating the light densities of the plurality of segments on the basis of the numerical analysis method.

18. A method according to claim 13, wherein the sixth step comprises obtaining a distribution of absorption coefficients in the object as the feature data of the plurality of segments.

19. A method according to claim 13, wherein the first step comprises causing said light-projecting unit to emit continuous light as the measurement light to be projected onto the object, and causing said light-receiving unit to continuously detect the exit measurement light from the object.

20. A method according to claim 13, wherein the first step comprises causing said light-projecting unit to emit pulse light as the measurement light to be projected onto the object, and causing said light-receiving unit to detect the exit measurement light from the object by a predetermined time-resolved measurement.

21. A method according to claim 13, wherein the first step comprises causing a light source included in said light-projecting unit to generate the measurement light, causing a plurality of optical fibers included in said light-projecting unit to project the measurement light emitted from said light source onto the object, and causing an optical switch which is included in said light-projecting unit and connects said light source and said plurality of optical fibers by using light branch paths to selectively open only one of a plurality of output terminals constituting said light branch paths.

22. A method according to claim 13, wherein the first step comprises causing a plurality of optical fibers included in said light-receiving unit to extract the measurement light from the object, causing a photoelectric conversion device included in said light-receiving unit to photoelectrically convert the incident measurement light from said plurality of optical fibers, and causing an optical switch which is included in said light-receiving unit and connects said plurality of optical fibers and said photoelectric conversion device by using light branch paths to selectively open only one of a plurality of input terminals constituting said light branch paths.

23. A method according to claim 13, wherein the first to sixth steps comprise causing a storage unit included in said arithmetic control mechanism to store various data detected by said light-receiving unit and various data calculated by an arithmetic unit included in said arithmetic control mechanism, and causing a controller included in said arithmetic control mechanism to sequentially control operations of said light-projecting unit, said light-receiving unit, and said arithmetic unit.

24. A method according to claim 13, further comprising the seventh step of causing a display to process input image data from said arithmetic control mechanism and to display a tomographic image of the object.