Method and apparatus for producing tomographic images

• US 4,809,312 A
• Filed: 07/22/1986
• Issued: 02/28/1989
• Est. Priority Date: 07/22/1986
• Status: Expired due to Term

• Current Assignee: American Science and Engineering Incorporated (OSI Systems Incorporated)
• Original Assignee: American Science and Engineering Incorporated (OSI Systems Incorporated)
• Inventors: Annis, Martin
• Primary Examiner(s): Fields, Carolyn E.
• Assistant Examiner(s): Hynds, Joseph A.
• Application Number:
  US06/888,019
• Time in Patent Office: 952 Days
• Field of Search: 378/86, 378/87, 378/88, 378/89, 378/90, 378/147, 378/149, 378/146, 378/6
• US Class Current: 378/146
• CPC Class Codes: G01N 23/203 Measuring back scattering

Abstract

Method and apparatus for the production of tomographic images includes a flying spot scanner to form, from a beam of penetrating radiation, a pencil beam sweeping over a line in space to define a sweep plane. An object to be examined is supported so that the pencil beam intersects the object along a path passing through the object and a selected slice of the object. A line collimator is provided for filtering radiation scattered by the object, the line collimator has a field of view which intersects the sweep plane in a bounded line so that the line collimator passes only that radiation scattered by elementary volumes of the object lying along the bounded line. A radiation detector responds to that portion of the scattered radiation which is passed by the line collimator.

Claims

1. A device useful in producing a tomographic image of a selected slice of an object to be examined comprising:

a source of penetrating radiation,

sweep means for forming energy from said source into a pencil beam and for repeatedly sweeping said pencil beam over a line in space to define a sweep plane,

first means for supporting an object to be examined so that said pencil beam intersects said object along a path passig through said object and said selected slice,

line collimating means for filtering radiation scattered by said object, said line collimating means having a field of view which intersects said sweep plane in a bounded line so that said line collimating means passes only radiation scattered by elementary volumes of said object lying along said bounded line, said line collimating means including a plurality of channels such substantially planar in form to collectively define said field of view, said channels oriented so that said pencil beam sweeps along said bounded line as a function of time, and

radiation detector means responsive to radiation passed by said line collimating means

2. The apparatus of claim 1 in which said first means includes means providing relative motion between said object and said radiation detector means and said line collimating means.

3. The apparatus of claim 2 in which said selected slice is planar and said relative motion is linear.

4. The apparatus of claim 2 in which said selected slice is a cylindrical surface and said motion is circular about an axis parallel to, and offset from said bounded line.

5. The apparatus of any of claims 1-4 in which said line collimating means and said radiation detector means lie between said source and said object.

6. The apparatus of claim 5 in which:

said radiation detector means includes first and second radiation detector elements located on different sides of a path traversed by radiation from said source to said object.

7. The apparatus of claim 5 in which:

said line collimating means includes first and second line collimating elements located on different sides of a path traversed by radiation from said source to said object.

8. The apparatus of claim 1 in which said line collimating means includes:

a radiation absorbing structure which has substantially similar cross-sections, in planes perpendicular to a plane defined by the sweeping motion of said pencil beam, including said plurality of channels, each channel lying along an imaginary line terminating at the intersection of said pencil beam and said selected slice and extending through a first face of said line collimating means, closer to said object than to said detector means, to a second face of said line collimating means closer to said detector means than to said object.

9. The apparatus of claim 8 including means for supporting said radiation detector means adjacent said line collimating means to provide, through said channels, a path for radiation scattered by said elementary volumes.

10. The apparatus of claim 8 in which said channels have parallel sides.

11. The apparatus of claim 8 in which said channels are separated by baffles, said baffles comprised of radiation absorbing material.

12. The apparatus of claim 11 in which at least one of said baffles has a first pair of straight parallel sides and a second pair of parallel sides, at least one of which includes a transition region substantially parallel to said first pair of sides.

13. The apparatus of claim 1 which further includes slice adjusting means for moving said line collimating means toward or away from said object to adjust a location of said selected slice relative to a surface of said line collimating means.

14. The apparatus of claim 1 in which said sweep means includes:

a fixed slit in a path of radiation emitted by said source to form a fan beam,

a chopper wheel rotated about an axis parallel to a plane defined by sweeping motion of said pencil beam, said chopper wheel including slit means for forming a sweeping pencil beam as said chopper wheel rotates moving said slit means to intersect said fan beam.

15. The apparatus of claim 1 wherein said sweep means includes means for forming a pencil beam with an asymmetrical cross-section.

16. The apparatus of claim 1 wherein said sweep means includes means for forming a pencil beam with beam breadth, measured perpendicular to a plane defined by said sweeping motion, and beam length, measured in said plane, wherein a ratio of beam length to beam breadth is substantially greater than unity.

17. The apparatus of claim 16 in which said ratio is about 10 or greater.

40. A device as recited in claim 1 in which said line collimating means comprises first and second collimating elements, each located opposite each other across said sweep plane, and said radiation detector means comprises first and second radiation detector elements, each located adjacent one of said first and second collimator elements and opposite each other across said sweep plane.

18. A method useful in generating a tomographic image of a selected slice of an object comprising the steps of:

providing a source of penetrating radiation,

forming a pencil beam from energy emitted by said source and repeatedly sweeping said pencil beam over a line in space,

supporting an object to be examined so that said pencil beam intersects said object along a path passing through said object and said selected slice,

filtering radiation scattered by said object to pass only radiation scattered by elementary volumes of said object lying along a line defined by a succession of intersections between said path and said selected slice by interposing a radiation absorbing structure with plural, substantially planar, radiation transmitting channels between said object and a radiation detector, said channels interposed relative to the sweeping pencil beam so that said pencil beam sweeps along said line as a function of time, and

detecting radiation passed by said filtered step.

19. The method of claim 18 in which said supporting step includes the step of providing relative motion between said object and said line in space which is swept by said pencil beam.

20. The method of claim 19 in which said selected slice is planar and said relative motion is linear.

21. The method of claim 19 in which said selected slice is a cylindrical surface and said motion is circular about an axis parallel to, and offset from said line defined by said succession of intersections.

22. The method of claim 18 which includes the further step of moving said object to adjust a location of said line defined by a succession of intersections between said path and said selected slice.

23. Apparatus useful for tomographic imaging of a selected slice of an object comprising:

radiation detector means providing, at any time a single output signal indicative of radiation reaching all portions of said detector means,

collimating means adjacent to said radiation detector means with a field of view to pass to said radiation detector means scattered energy originating within said field of view, said collimating means including a plurality of channels each substantially planar in form to collectively define said field of view,

a source of penetrating radiation,

sweep means for forming radiation from said source into a pencil beam and for sweeping said pencil beam over a line in space so as to define a sweep plane, said sweep plane intersecting said field of view in a bounded line, said sweep means sweeping said pencil beam over said bounded line as a function of time,

means for supporting an object to be imaged so that said bounded line lies within a selected slice which is to be imaged,

means for providing relative motion between said object and said collimating means so that, as a function of time said bounded line traces said selected slice, and

image means responsive to a time sequence of output signals for forming an image.

24. The apparatus of claim 23 in which said selected slice is planar and said relative motion is linear.

25. The apparatus of claim 23 in which said selected slice is a cylindrical surface and said motion is circular about an axis parallel to, and offset from said bounded line.

26. The apparatus of any of claims 23-25 in which said collimating means and said radiation detector means lie between said source and said object.

27. The apparatus of claim 26 in which:

said radiation detector means includes first and second radiation detector elements located on different sides of a path traversed by radiation from said source to said object.

28. The apparatus of claim 26 in which:

said collimating means includes first and second line collimating elements located on different sides of a path traversed by radiation from said source to said object.

29. The apparatus of claim 23 in which said collimating means includes:

a radiation absorbing structure which has a cross-section, in a plane perpendicular to a plane defined by the sweeping motion of said pencil beam, including a plurality of channels, each channel lying along an imaginary line terminating at the intersection of said pencil beam and said selected slice and extending through a first face of said collimating means, closer to said object than to said detector means, to a second face of said collimating means closer to said detector means than to said object.

30. The apparatus of claim 29 including means for supporting said radiation detector means adjacent said collimating means to provide, through said channels, a path for radiation scattered by a region within said object adjacent said bounded line.

31. The apparatus of claim 29 in which said channels have parallel sides.

32. The apparatus of claim 29 in which said channels are separated by baffles, said baffles comprised of radiation absorbing material.

33. The apparatus of claim 32 in which at least one of said baffles has a first pair of straight parallel sides and a second pair of parallel sides, at least one of which includes a transition region substantially parallel to said first pair of sides.

34. The apparatus of claim 32 which further includes slice adjusting means for moving said collimating means toward or away from said object to adjust a location of said selected slice relative to a surface of said collimating means.

35. The apparatus of claim 23 in which said sweep means includes:

a fixed slit in a path of radiation emitted by said source to form a fan beam,

a chopper wheel rotated about an axis parallel to a plane defined by sweeping motion of said pencil beam, said chopper wheel including slit means for forming a sweeping pencil beam as said chopper wheel rotates moving said slit means to intersect said fan beam.

36. The apparatus of claim 23 wherein said sweep means includes means for forming a pencil beam with an asymmetrical cross-section.

37. The apparatus of claim 23 wherein said sweep means includes means for forming a pencil beam with beam breadth, measured perpendicular to a plane defined by said sweeping motion, and beam length, measured in said plane, wherein a ratio of beam length to beam breadth is substantially greater than unity.

38. The apparatus of claim 37 in which said ratio is about 10 or greater.

39. The apparatus of claim 23 wherein:

said collimating means comprises plural channels in a radiation absorbing structure, each of said channels being substantially planar to define plural channel planes, said channel planes intersecting said selected slice in said bounded line.

41. A device useful in producing a tomographic image of a selected slice of an object to be examined comprising:

a source of penetrating radiation,

sweep means for forming energy from said source into a pencil beam and for repeatedly sweeping said pencil beam over a line in space to define a sweep plane,

first means for supporting an object to be examined so that said pencil beam intersects said object and said selected slice,

second means for detecting radiation scattered, at any instant, by one of a group of selected volume elements in said slice, said second means subtending a large solid angle relative to said one selected volume element, said second means including;

radiation detector means developing an any instant in time a single signal reflecting radiation impinging on said radiation detector means, and

a collimator located between said object and said radiation detector means, said collimator including;

a plurality of radiation transmitting channels collectively establishing a field of view which intersects said sweep plane in a preferential line which is a locus of a plurality of said selected volume elements so that said collimator passes radiation scattered by different elementary volume elements of said object lying along said preferential line as said sweep illuminates the different volume elements lying along said preferential line.

42. A device as recited in claim 41 wherein said collimator has a plane of symmetry which coincides with said sweep plane.

43. A device as recited in claim 41 wherein said collimator has a plurality of substantially planar radiation transmitting channels to define said field of view.

44. The apparatus of claim 41 in which said first means includes means providing relative motion between said object and said radiation detector means and collimator.

45. The apparatus of claim 44 in which said selected slice is planar and said relative motion is linear.

46. The apparatus of claim 44 in which said selected slice is a cylindrical surface and said motion is circular about an axis parallel to, and offset from said preferential line.

47. The apparatus of any of claims 41-46 in which said collimator and said radiation detector means lie between said source and said object.

48. The apparatus of claim 47 in which:

said radiation detector means includes first and second radiation detector elements located on different sides of said sweep plane.

49. The apparatus of claim 47 in which:

said collimator includes first and second collimator elements located on different sides of said sweep plane.

50. The apparatus of claim 41 in which said collimator includes:

a radiation absorbing structure which has substantially similar cross-sections, in planes perpendicular to said sweep plane, including a plurality of channels, each said channel lying along an imaginary line terminating at the intersection of said pencil beam and said selected slice and extending through a first face of said collimator, closer to said object than to said radiation detector means, to a second face of said collimator closer to said radiation detector means than to said object.

51. The apparatus of claim 50 including means for supporting said radiation detector means adjacent said collimator to provide, through said channels, a path for radiation scattered by said elementary volume elements.

52. The apparatus of claim 50 in which said channels have parallel sides.

53. The apparatus of claim 50 in which said channels are separated by baffles, said baffles comprised of radiation absorbing material.

54. The apparatus of claim 53 in which at least one of said baffles has a first pair of straight parallel sides and a second pair of parallel sides, at least one of which includes a transition region substantially parallel to said first pair of sides.

55. The apparatus of claim 41 which further includes slice adjusting means for moving said collimator toward or away from said object to adjust a location of said selected slice relative to a surface of said collimator.

56. The apparatus of claim 41 in which said sweep means includes:

a fixed slit in a path of radiation emitted by said source to form a fan beam,

a chopper wheel rotated about an axis parallel to a plane defined by sweeping motion of said pencil beam, said chopper wheel including slit means for forming a sweeping pencil beam as said chopper wheel rotates moving said slit means to intersect said fan beam.

57. The apparatus of claim 41 wherein said sweep means includes means for forming a pencil beam with an asymmetrical cross-section.

58. The apparatus of claim 41 wherein said sweep means includes means for forming a pencil beam with beam breadth, measured perpendicular to said sweep plane, and beam length, measured in said sweep plane, wherein a ratio of beam length to beam breadth is substantially greater than unity.

59. The apparatus of claim 58 in which said ratio is about 10 or greater.