High resolution radiation imaging system

• US 5,340,988 A
• Filed: 04/05/1993
• Issued: 08/23/1994
• Est. Priority Date: 04/05/1993
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Srinivas, Chukka, Kingsley, Jack D.
• Primary Examiner(s): Hannaher, Constantine
• Application Number:
  US08/043,116
• Time in Patent Office: 505 Days
• Field of Search: 250/370.11, 250/370.09, 250/370.08, 250/334, 250/332, 358/213.28
• US Class Current: 250/370.09
• CPC Class Codes: G01T 1/20184 Detector read-out circuitry, e.g. for clearing of traps, compensating for traps or compensating for direct hits
• CPC Class Codes: G01T 1/2019 Shielding against direct hits
• CPC Class Codes: G01T 1/2928 using solid state detectors
• CPC Class Codes: H04N 25/48 Increasing resolution by shifting the sensor relative to the scene
• CPC Class Codes: H04N 5/32 Transforming X-rays cameras or camera modules for generating image signals from X-rays H04N23/30; circuitry of SSIS for transforming X-rays into image signals H04N25/30

Abstract

A radiation imaging system includes an image detector assembly coupled to an image processor. The image detector assembly includes a photosensor pixel array which is disposed in a plurality of sequential imaging positions pursuant to a predetermined imaging cycle. The image processor stores the respective image data signals from each photosensor pixel in the array from each respective imaging position in a given imaging cycle in an unfiltered interleaved data set, and then apply the unfiltered data to a deblurring filter to generate a non-aliased high resolution data set appropriate for driving a display and analysis module.

Claims

1. A radiation imaging system comprising:

a photosensor pixel array, said array comprising a plurality of pixels having a predetermined photosensor pixel pitch between adjoining pixels, each of said photosensor pixels being adapted to generate a respective image data signal, said array being adapted to be sequentially disposed in selected ones of a plurality of sequential imaging positions pursuant to a predetermined imaging cycle, each of said sequential imaging positions being selected such that the area imaged by each respective pixel overlaps a portion of the area imaged by said respective pixel while disposed in the preceding imaging position in said predetermined imaging cycle so as to oversample the imaged area; and

an image processor coupled to said photosensor pixel array so as to receive the respective image data signals generated by said photosensor pixels, said image processor being adapted to store said respective image data signals generated during an imaging cycle by said photosensor pixels in each of said respective sequential imaging positions as an unfiltered data set, said image processor further comprising a deblurring filter adapted to selectively filter said data set to generate a non-aliased fine resolution data set having spatial resolution greater than the imaging system Nyquist frequency determined by the pixel pitch of said photosensor array.

2. The imaging system of claim 1 wherein said plurality of sequential imaging positions comprises respective first, second, third, and fourth sequential imaging positions.

3. The imaging system of claim 2 wherein said first, second, third, and fourth imaging positions are disposed such that the distance between adjacent sequential imaging positions along a selected axis of movement of said photosensor pixel array is substantially one-half of said predetermined pitch of said pixels.

4. The imaging system of claim 3 wherein said first through fourth imaging positions are disposed so as to form the corners of a square with sides having a length of one-half said predetermined pitch of said pixels.

5. The imaging system of claim 2 wherein said photosensor pixel array comprises a plurality of pixels arranged in N rows and M columns.

6. The imaging system of claim 5 wherein said image processor is adapted to store in each unfiltered data set one image data signal generated by each respective photosensor pixel in each of said respective sequential imaging positions.

7. The imaging system of claim 6 wherein said deblurring filter is adapted such that said fine resolution data set generated by said filter resolves objects having spatial frequency components above the imaging system'"'"'s Nyquist frequency.

8. The imaging system of claim 7 wherein said deblurring filter is adapted such that said fine resolution data set generated by said filter exhibits a spatial resolution capable of resolving objects of a size of one-half the predetermined photosensor pixel pitch.

9. The imaging system of claim 8 wherein said deblurring filter is adapted to form said fine resolution image in accordance with the equation:

##EQU2## wherein;

F(W_x, W_y) is the Fourier transform of the desired high resolution image;

G(W_x, W_y)is the Fourier transform of the unfiltered image;

H*(W_x, W_y)is the Fourier transform of the point spread function of the imaging system;

|H(W_x, W_y)| is the modulation transfer function of the imaging system;

a represents a positive constant selected to reduce amplification of G at higher spatial frequencies so as to limit the high frequency noise.

10. The imaging system of claim 8 wherein said deblurring filter is adapted to form said fine resolution image in accordance with the convolution:

space="preserve" listing-type="equation">f(m,n)=Σ

.sub.p,q k(m-p,n-q)g(p,q)

in which k(m-p, n-q) represents the inverse Fourier transform of K, the Wiener filter spectrum; and

g(p,q) represents the unfiltered image.

11. The imaging system of claim 5 further comprising a display and analysis module coupled to said image processor and adapted to receive the high resolution data set signals.

12. The imaging system of claim 11 wherein said display and analysis module comprises a display array having at least 2N by 2M display pixels, said display array having a pitch of about one-half said predetermined imaging pixel pitch.

13. The imaging system of claim 2 wherein said imaging system further comprises a displacement mechanism adapted to sequentially position said photosensor array at respective ones of said imaging positions in accordance with said predetermined imaging cycle.

14. The imaging system of claim 13 wherein said displacement mechanism comprises:

a displacement platform, a first drive cam coupled to said displacement platform such that motion of said drive cam is translated into movement of said displacement platform along a first selected axis, and a second drive cam coupled to said displacement platform such that motion of said drive cam is translated into movement of said displacement platform along a second selected axis.

15. The imaging system of claim 14 wherein each of said drive cams has a respective eccentric shape selected to cause displacement of said platform along the respective selected axis upon rotation of the respective cam.

16. The imaging system of claim 15 wherein said displacement mechanism is adapted such that each of said first and second axes are disposed so that selective movement of said displacement platform along said respective axes displaces said photosensor pixel army to a selected one of said imaging positions.

17. The imaging system of claim 16 wherein said predetermined pitch between photosensor pixels is about 100 microns.

18. The imaging system of claim 17 wherein said imaging system is adapted to detect and image incident x-rays.

19. A method of generating a high resolution image of incident radiation, comprising the steps of:

sequentially positioning an array of photosensor pixels in first through Kth imaging positions in accordance with a predetermined imaging cycle, said photosensor pixels being disposed in said array in rows and columns having a predetermined photosensor pixel pitch therebetween, each of said sequential imaging positions being selected such that the area imaged by each respective pixel overlaps a portion of the area imaged by said respective pixel while disposed in the preceding imaging position in said predetermined imaging cycle so as to oversample the imaged area;

storing the respective image data signals generated in each of the first through Kth imaging positions to form an unfiltered data set; and

applying said unfiltered data set to a deblurring filter to form a high resolution data set having spatial resolution greater than the Nyquist frequency determined by the pixel pitch of said photosensor array;

said first through Kth imaging positions in said predetermined imaging cycle being disposed such that aliasing errors are cancelled in said high resolution data set.

20. The process of claim 19 wherein the step of sequentially positioning said array of photosensor pixels further comprises the steps of:

displacing said photosensor pixel array in a selected sequence so that said array is respectively disposed at each of four imaging positions during said imaging cycle.

21. The method of claim 20 wherein the step of displacing said array further comprises sequentially translating said array along a first axis and a second axis, said first and second axes being orthogonal.

22. The method of claim 21 wherein the distance along said first and second axes between respective ones of said four imaging positions correspond to one-half the photosensor pixel pitch.

23. The method of claim 22 wherein the step of applying said unfiltered data to a deblurring filter to form said high resolution data set comprises filtering said unfiltered data set to generate an image having a spatial resolution corresponding to one-half the photosensor pixel pitch.

24. The method of claim 23 wherein the step of applying said unfiltered data set to a deblurring filter further comprises computing said high resolution image data set in accordance with the following relationship:

##EQU3## wherein;

F(W_x, W_y) is the Fourier transform of the desired high resolution image;

G(W_x, W_y) is the Fourier transform of the unfiltered image;

H*(W_x, W_y)is the Fourier transform of the point spread function of the imaging system;

|H(W_x, W_y)| is the modulation transfer function of the imaging system;

a represents a positive constant selected to reduce amplification of G at higher spatial frequencies so as to limit the high frequency noise.

25. The method of claim 23 wherein the step of applying said unfiltered data set to a deblurring filter further comprises computing said high resolution image data set in accordance with the following convolution:

space="preserve" listing-type="equation">f(m,n)=Σ

.sub.p,q k(m-p,n-q)g(p,q)

in which k(m-p, n-q) represents the inverse Fourier transform of K, the Wiener filter spectrum; and

g(p,q) represents the unfiltered image.

26. The method of claim 25 further comprising the step of driving a display and analysis module to present said high resolution data.

27. A method for increasing the resolvable spatial frequency of a digital radiation imaging system having a plurality of imaging devices, the method comprising the steps of:

generating multiple exposures of an object to be imaged, each of said exposures being taken in a respective imaging position, each imaging position being disposed in a predetermined spatial relation with regard to the remaining imaging positions such that the area imaged in each respective imaging position overlaps a portion of the area imaged in the preceding imaging position;

registering the respective exposures generated in an unfiltered non-aliased data set; and

deblurring said unfiltered data set to generate a non-aliased high resolution data set having spatial resolution greater than the Nyquist frequency determined by the pitch of said imaging devices.

28. The method of claim 27 wherein the step of generating multiple exposures further comprises the steps of selectively sequentially displacing an array of photosensor pixels to be disposed in respective ones of said imaging positions in accordance with an imaging cycle.

29. The method of claim 28 wherein the step of deblurring said image said data said further comprises the step of passing said data set through a deblurring filter, said deblurring filter comprising a Wiener filter.

30. The method of claim 29 wherein said imaging positions are selected to cancel aliasing errors in said high resolution data set.

31. An x-ray imaging system comprising:

a photosensor pixel array, said array comprising a plurality of pixels having a predetermined photosensor pixel pitch between adjoining pixels, each of said photosensor pixels being adapted to generate a respective image data signal, said array being adapted to be sequentially disposed in selected ones of a plurality of sequential imaging positions pursuant to a predetermined imaging cycle, each of said sequential imaging positions being selected such that the area imaged by each respective pixels overlaps a portion of the area imaged by said respective pixel while disposed in the preceding imaging position in said predetermined imaging cycle so as to oversample the imaged area; and

an image processor coupled to said photosensor pixel array so as to receive the respective image data signals generated by said photosensor pixels, said image processor being adapted to store said respective image data signals generated during an imaging cycle by said photosensor pixels in each of said respective sequential imaging positions as an unfiltered data set, said image processor further comprising a deblurring filter adapted to selectively filter said data set to generate a non-aliased fine resolution data set having spatial resolution greater than the Nyquist frequency determined by the pixel pitch of said photosensor array; and

a display and analysis module coupled to said image processor and adapted to be driven by said fine resolution data to generate an output fine resolution array, said output fine resolution array having a greater number of pixels than said photosensor pixel array, said imaging system being adapted such that each of the fine resolution pixels are driven by an individually-variable signal.

32. The imaging system of claim 31 wherein said plurality of sequential imaging positions comprises respective first, second, third, and fourth sequential imaging positions.

33. The imaging system of claim 32 wherein said first, second, third, and fourth imaging positions are disposed such that in each respective imaging position each photosensor pixel is centered on one of the respective areas representing a corresponding pixel element in the output fine resolution array, and further the four imaging positions are disposed such that each area representing a pixel element in said output high resolution array is centered on a respective photosensor pixel in only one of said four imaging positions.

34. The imaging system of claim 33 wherein the distance between adjacent sequential imaging positions along a selected axis of movement of said photosensor pixel array is substantially one-half of said predetermined pitch of said photosensor pixels.

35. The imaging system of claim 34 wherein said imaging system further comprises a displacement mechanism adapted to move said photosensor array so as to selectively dispose said photosensor array in a selected one of said imaging positions, said displacement mechanism comprising:

a displacement platform, a first drive cam coupled to said displacement platform such that motion of said drive cam is translated into movement of said displacement platform along a first selected axis, and a second drive cam coupled to said displacement platform such that motion of said drive cam is translated into movement of said displacement platform along a second selected axis.

36. The imaging system of claim 35 wherein each of said drive cams has a respective eccentric shape selected to cause displacement of said platform along the respective selected axis upon rotation of the respective cam.

37. The imaging system of claim 36 wherein said displacement mechanism is adapted such that each of said first and second axes are disposed so that selective movement of said displacement platform along said respective axes displaces said photosensor pixel array to a selected one of said imaging positions.

38. The imaging system of claim 37 further comprising a scintillator optically coupled to said photosensor pixel array and disposed to receive radiation passing from an object to be imaged.

39. The imaging system of claim 37 wherein said photosensor array comprises a radiation absorptive photosensitive material such that radiation incident on said imaging system is absorbed by said material and converted into mobile charge particles to generate said image data signals.