Title: Method and apparatus for tomographic examination of an object by penetrating radiation

What is claimed is:

1. Apparatus for examining at least part of an object using penetrating radiation, such as X-rays or gamma rays, comprising:

(a) transmitting means for transmitting a plurality of photons of penetrating radiation through the object along a plurality of paths; and

(b) detecting means disposed on the opposite side of the object from said transmitting means for detecting substantially all the plurality of individual photons emerging from the object along each of the plurality of paths, wherein said detecting means comprises scintillator means having a wall lining absorbent of penetrating ray photons so as to be self-collimating.

2. The apparatus of claim 1, wherein:

said self-collimating scintillator means has a longitudinal axis and is disposed so that the paths of the photons passing through the object from said transmitting means and toward said scintillator means are substantially parallel to said longitudinal axis.

3. The apparatus of claim 2, wherein:

(a) said detecting means has a detecting surface through which photons enter said detecting means; and

(b) said detecting surface of said detecting means is substantially perpendicular to said longitudinal axis.

4. The apparatus of claim 2, wherein said self-collimating scintillator means comprises:

a scintillator of a particular geometric configuration for collimating and detecting photons, said scintillator having an entry surface disposed within a plurality of lateral surfaces through which photons enter said scintillator.

5. The apparatus of claim 4, wherein:

the width of said entry surface is sized so that substantially all of the penetrating ray photons detected pass through said entry surface and have paths within a small angular deviation from a path parallel to said longitudinal axis.

6. The apparatus of claim 5, wherein:

the length of said scintillator is sufficiently long to allow photons which have paths within a small angular deviation from a path parallel to said longitudinal axis sufficient travel time within said scintillator to be detected.

7. The apparatus of claim 4, wherein said scintillator comprises:

scintillating plastic.

8. The apparatus of claim 4, wherein:

said wall lining is disposed along a lateral surface of said scintillator for absorbing penetrating ray photons which are not detected prior to the time such photons reach said lateral surface.

9. The apparatus of claim 1, wherein said transmitting means transmits a substantially fan-shaped set of rays and said detecting means comprises:

a plurality of scintillator means, each scintillator means having a wall lining absorbent of penetrating ray photons so as to be self-collimating, wherein each of said self-collimating scintillator means detects photons emerging from the object along a predetermined path.

10. The apparatus of claim 9, wherein:

(a) each of said self-collimating scintillator means has a longitudinal axis which is disposed substantially perpendicular to an arc which has its center located at said transmitting means situated opposite said self-collimating sensing means; and

(b) substantially all of the penetrating ray photons detected by each of said self-collimating scintillator means are photons whose paths are within a small angular deviation from a path parallel to its longitudinal axis.

11. The apparatus of claim 10, wherein:

(a) the self-collimating scintillator means has an entry surface through which photons enter said scintillator means; and

(b) said entry surface of said self-collimating scintillator means is substantially perpendicular to its longitudinal axis.

12. The apparatus of claim 11, wherein:

(a) the detecting means has a surface facing the transmitting means opposite it; and

(b) the proportion of the surface of said detecting means which is comprised of entry surfaces for penetrating ray photons is greater than 80 percent.

13. The apparatus of claim 1, wherein said detecting means comprises:

photon counting means for counting the number of individual penetrating ray photons detected along a ray path and generating an output signal representative of the number of photons detected.

14. The apparatus of claim 1, wherein:

(a) said scintillator means converts energy from penetrating ray photons into light photons;

(b) said detecting means further comprises photomultiplier means optically coupled to said scintillator means for detecting the light photons and generating a signal representative of the penetrating ray photons detected by said scintillator means; and

(c) said scintillator means further comprises reflective lining means so that said scintillator means also collimates a substantial portion of the light photons generated by said scintillator means wherein the collimated light photons can be efficiently guided a substantial distance to said photomultiplier means.

15. The apparatus of claim 1, wherein:

(a) said scintillator means comprises:

a high-speed scintillator having a very fast decay time for detecting substantially all of the penetrating ray photons passing through the object along one of the plurality of paths and converting the energy of the penetrating ray photons into a plurality of light photons within a sufficiently short time interval after detection such that substantially all light photons associated with each detected penetrating ray photon are generated within different time intervals; and

(b) said detecting means further comprises:

(1) photomultiplier means for detecting the light photons associated with each penetrating ray photon detected and for generating a signal for each plurality of light photons associated with each individual penetrating ray photon detected; and

(2) counting means for counting the signals generated by said photomultiplier means and generating output signals representative of the number of individual penetrating ray photons detected.

16. The apparatus of claim 1, wherein:

(a) a portion of the penetrating ray photons transmitted toward the object is deflected by the object from its initial path to form secondary photons of penetrating radiation;

(b) the photons transmitted through the object along the plurality of paths are primary photons;

(c) said self-collimating scintillator means has a longitudinal axis and said scintillator means is disposed so that the paths of primary photons is substantially parallel to its longitudinal axis; and

(d) substantially all the penetrating ray photons detected by said self-collimating scintillator means are primary and secondary photons entering said detecting means whose paths are within a small angular deviation from a path which is parallel to said longitudinal axis whereby the proportion of secondary photons detected to total photons detected is small.

17. The apparatus of claim 16, wherein said self-collimating scintillator means comprises:

(a) a high-speed scintillator having a very fast decay time for converting energy from the primary and secondary photons detected into light photons within a sufficiently short time interval after detection such that substantially all the light photons associated with each ray photon detected are generated within different time intervals;

(b) photomultiplier means optically coupled to said scintillator for detecting the plurality of light photons generated by each of said primary and secondary photons detected and generating a primary signal for each plurality of light photons associated with a primary photon and a secondary signal for each plurality of light photons associated with a secondary photon;

(c) discriminator means for discriminating between primary and secondary signals received from said photomultiplier means and for generating event signals for each primary signal received; and

(d) primary signal counter means for counting the number of primary signals and generating output signals representative of the number of primary signals counted which are useful in determining the intensity of the penetrating radiation passing through the object along each of the plurality of paths.

18. The apparatus of claim 17, wherein said high-speed scintillator comprises:

scintillating plastic.

19. Apparatus for examining at least part of an object using penetrating radiation such as X-rays or gamma rays, comprising:

(a) a plurality of transmitting means angularly disposed at intervals about the object to be examined for transmitting photons of penetrating radiation through a planar section of the object wherein each transmitting means transmits a plurality of penetrating ray photons along a plurality of paths through the planar section to form a set of rays which is disposed in the planar section at an angle different from the angular disposition of sets of rays formed by other transmitting means;

(b) a plurality of detecting means disposed at intervals about the object to be examined for detecting the plurality of photons in the sets of rays transmitted through the object wherein each of said detecting means is disposed opposite one of said transmitting means for detecting penetrating ray photons in the set of rays from said opposite transmitting means wherein said detecting means comprises:

a plurality of scintillator means wherein each of said scintillator means has a wall lining absorbent of penetrating ray photons so as to be self-collimating, whereby said plurality of self-collimating scintillator means causes said detecting means to be self-collimating.

20. The apparatus of claim 19, further comprising:

means for sequentially discharging each of said plurality of transmitting means.

21. The apparatus of claim 20, wherein said means for sequentially discharging comprises:

means for sequentially pulsing each of said plurality of transmitting means whereby only one of the transmitting means is discharged at any particular time.

22. The apparatus of claim 19, further comprising:

mounting means on which said plurality of transmitting means and said plurality of self-collimating detecting means are mounted stationary relative to the other.

23. The apparatus of claim 22, further comprising:

means for inclining said mounting means relative to the object under examination whereby the sets of rays from said transmitting means can be transmitted through different planar sections of the object.

24. The apparatus of claim 22, wherein:

(a) said plurality of transmitting means comprises 2N+1 transmitting means, where N is any integer greater than zero; and

(b) said plurality of self-collimating detecting means comprises 2N+1 detecting means.

25. The apparatus of claim 24, wherein:

said 2N+1 transmitting means are respectively disposed at substantially regular intervals along the circumference of a circle inside which the object to be examined is situated.

26. The apparatus of claim 19, wherein each of said self-collimating detecting means generates a plurality of output signals representative of the radiation absorption by the object from said transmitting means situated opposite said self-collimating detecting means and further comprising:

means for evaluating the output signals to obtain signals representative of the variable coefficient of radiation absorption of the planar section of the object.

27. The apparatus of claim 26, wherein every element of a matrix of elements defining the planar section of the object under examination is intersected by rays from a plurality of transmitting means and wherein said means for evaluating the output signals comprises:

processing means for obtaining signals representative of the radiation absorption coefficient of each element of the matrix of elements in the planar section under examination.

28. The apparatus of claim 27, wherein said processing means comprises:

transformation means for determining matrix signals indicative of the values of the coefficients of radiation absorption of each of said plurality of elements in the matrix of elements.

29. The apparatus of claim 28, wherein said processing means further comprises:

iterative means for processing the matrix signals by a process of successive approximations to obtain a resultant matrix signal which represents more accurately the coefficient of radiation absorption of the matrix elements than the resultant matrix signals determined solely by transformation means.

30. The apparatus of claim 28, wherein the matrix signals determined by said transformation means includes a reconstruction artifact signal and said processing means further comprises:

artifact removal means for removing the reconstruction artifact signal from said matrix signals.

31. The apparatus of claim 18, wherein:

(a) said self-collimating scintillator means has a longitudinal axis and is disposed so that the paths of the plurality of photons in the set of rays passing through the object from said transmitting means opposite said scintillator means are substantially parallel to said longitudinal axis; and

(b) substantially all of the penetrating ray photons detected by said self-collimating scintillator means are photons which enter said scintillator means and whose paths are within a small angular deviation from a path which is parallel to the longitudinal axis of said scintillator means whereby substantially all photons detected by said self-collimating scintillator means are photons in the set of rays which pass through the object from the transmitting means opposite said self-collimating scintillator means.

32. The apparatus of claim 31, wherein:

said self-collimating scintillator means has an entry surface which is substantially perpendicular to said longitudinal axis through which photons enter said scintillator means.

33. The apparatus of claim 19, wherein:

said transmitting means transmits a substantially fan-shaped set of rays and said plurality of self-collimating scintillator means comprising said detecting means has a predetermined configuration such that the longitudinal axes of said plurality of scintillator means are substantially perpendicular to an arc which has its center located at said transmitting means situated opposite said detecting means, said scintillator means further having an entry surface through which photons enter wherein each of said scintillator means detects only photons whose paths are within a small angular deviation from a path parallel to its longitudinal axis.

34. The apparatus of claim 19, wherein:

(a) a portion of the penetrating ray photons transmitted from each of said transmitting means is deflected by the object from its initial path to form secondary photons of penetrating radiation;

(b) the photons passing through the object along the plurality of paths in each set of rays are primary photons; and

(c) said self-collimating scintillator means detect both primary and secondary photons wherein the proportion of secondary photons detected to the total photons detected by each of said scintillator means is small.

35. The apparatus of claim 34, wherein each of said self-collimating scintillator means comprises:

(a) a high speed scintillator having a very fast decay time for converting the primary and secondary photons detected into light photons within a sufficiently short time interval after detection such that substantially all the light photons associated with each photon detected are generated within a different time interval from the light photons associated with a subsequently detected penetrating ray photon;

(b) photomultiplier means optically coupled to said scintillator for detecting the plurality of light photons generated by each of said primary and secondary photons detected and generating a primary signal for each pluarlity of light photons associated with a primary photon and a secondary signal for each plurality of light photons associated with a secondary photon;

(c) discriminator means for discriminating between primary and secondary signals received from said photomultiplier means and generating event signals for each primary signal received; and

(d) counting means for counting the number of primary signals and generating output signals representative of the number of primary photons detected along the plurality of ray paths defined by the set of rays passing through the object from said transmitting opposite said detecting means.

36. Apparatus for examining at least part of an object using penetrating radiation, such as X-rays or gamma rays, comprising:

(a) transmitting means for transmitting a pluarlity of photons of penetrating radiation through the object along a path;

(b) scintillator means for detecting the penetrating ray photons and converting energy from the penetrating ray photons into light photons, said scintillator means comprising:

(1) scintillating plastic of a particular geometric configuration having an entry surface through which penetrating ray photons enter said scintillating plastic and lateral surfaces about said entry surface which collimates both the penetrating ray photons and the light photons and which guides the light photons;

(2) lining means disposed along said lateral walls for absorbing penetrating ray photons entering said scintillating plastic whose paths are at a substantial angular deviation from a path perpendicular to said entry surface and which are not detected prior to the time such photons reach one of said lateral surfaces;

(3) reflector means disposed between said lining means and said lateral surfaces for increasing the collimating efficiency and guiding efficiency of said scintillator means for light photons; and

(c) photomultiplier means optically coupled to said scintillator means for detecting the light photons and generating a signal representative of the penetrating ray photons detected, wherein a substantial portion of the light photons generated by the detection of penetrating ray photons are collimated and efficiently guided a substantial distance to said photomultiplier means.

Other info:


Inventors: Morgan, Ira L. (10305B Golden Meadow Dr., Austin, TX, 78758)
Sudarshan, George E. C. (7012 Northledge Dr., Austin, TX)
Mitchell, Alvin L. (Austin, TX)
Coose, James P. (Austin, TX)
Ellinger, Hunter D. (Austin, TX)
Jagger, James W. (Austin, TX)

Application Number: 05/879439
Filing Date: 1978-02-21
Publication_date: 1981-08-18
Assignee: Morgan, Ira Lon

Primary Class(es): 378/9 250/363.020
Other Classes: A61B6/03; G01N21/00
US Patent Ref:

3778614	December, 1973	Hounsfield	250/363S	METHOD AND APPARATUS FOR MEASURING X- OR .gamma.-RADIATION ABSORPTION OR TRANSMISSION AT PLURAL ANGLES AND ANALYZING THE DATA
3922552	November, 1975	Ledley	250/445T	Diagnostic X-ray systems
3937965	February, 1965	Vasseur	250/445T	Radiography apparatus
3978337	August, 1976	Nickles et al.	250/363R	Three-dimensional time-of-flight gamma camera system
3984689	October, 1976	Arseneau	250/363S	Scintillation camera for high activity sources
4057725	November, 1977	Wagner	250/360	Device for measuring local radiation absorption in a body

Other Refs: Other References: Nuclear Enterprises Inc. Brochure, "Plastic Scintillators (Light Pipes and Cerenkov Detectors)".

Primary Examiner: Smith, Alfred E.
Assistant Examiner: O'hare, Thomas P.
Attorney: Keys, Jerry M.