Image reconstruction method using Hilbert transform

1. A method of determining an image data value at a point of reconstruction in a computed tomography (CT) image of a scanned object, comprising:

obtaining projection data of the scanned object;

filtering the obtained projection data with both a one-dimensional ramp filter and a Hilbert filter to generate filtered data;

applying a backprojection operator with inverse distance weighting to said filtered data to generate the image data value at the point of reconstruction in the CT image; and

displaying the generated image data value, wherein the filtering step comprises

applying projection subtraction to the obtained projection data to generate subtracted data;

applying the Hilbert filter to the subtracted data to generate Hilbert-filtered data; and

applying projection addition to the Hilbert-filtered data and ramp-filtered data to generate the filtered data, the ramp-filtered data being generated by filtering the obtained projection data with the one-dimensional ramp filter, and

wherein the step of obtaining projection data produces two-dimensional projections and the step of applying the backprojection operator is applied only to said filtered data contained within a Tam window.

2. The method of claim 1 , further comprising:

repeating said applying step for a plurality of points of reconstruction in the CT image to obtain a plurality of image data values; and

generating the CT image by arranging said plurality of image data values according to said plurality of points of reconstruction.

3. The method of claim 1 , further comprising:

repeating the step of applying the backprojection operator for a plurality of points of reconstruction in a volume of interest to obtain a plurality of image data values; and

generating a CT volume by arranging said plurality of image data values according to said plurality of points of reconstruction in the volume of interest.

4. The method of claim 1 , wherein the filtering step comprises:

filtering said projection data with a modified ramp filter.

5. The method of claim 1 , wherein the filtering step comprises:

filtering said projection data with a modified ramp filter with an offset.

6. The method of claim 1 , wherein the obtaining step comprises:

obtaining the projection data using a CT system having one of a circular source trajectory, a helical source trajectory, and a saddle source trajectory.

7. The method of claim 1 , wherein the filtering step comprises:

filtering the obtained projection data using one of (1) horizontal filtering, (2) tangential filtering, (3) rotated filtering, and (4) Katsevich filtering.

8. The method of claim 1 , wherein the obtaining step comprises:

obtaining the projection data using a projection range that satisfies Λ≧π+2 arcsin (r FOV /R), wherein Λ is the projection range, r FOV is a radial measurement of a field of view (FOV), and R is a radial measurement of a source trajectory.

9. A method of determining an image data value at a point of reconstruction in a computed tomography (CT) image of a scanned object, comprising:

obtaining projection data of the scanned object;

filtering the obtained projection data with both a one-dimensional ramp filter and a Hilbert filter to generate filtered data;

applying a backprojection operator with inverse distance weighting to said filtered data to generate the image data value at the point of reconstruction in the CT image; and

displaying the generated image data value, wherein the filtering step comprises

applying projection subtraction to the obtained projection data to generate subtracted data;

applying the Hilbert filter to the subtracted data to generate Hilbert-filtered data; and

applying projection addition to the Hubert-filtered data and ramp-filtered data to generate the filtered data, the ramp-filtered data being generated by filtering the obtained projection data with the one-dimensional ramp filter, the method further comprising

applying redundancy weighting to said filtered data to generate weighted data,

wherein the step of applying the backprojection operator is applied to said weighted data to generate the image data value at the point of reconstruction in the CT image.

10. The method of claim 9 , further comprising:

repeating said step of applying the backprojection operator for a plurality of points of reconstruction in a region of interest within a same horizontal plane as the point of reconstruction to obtain a plurality of image data values; and

generating the CT image by arranging said plurality of image data values according to said plurality of points of reconstruction.

11. The method of claim 10 , further comprising:

repeating said steps of (1) applying redundancy weighting, and (2) repeating said step of applying the backprojection operator for a plurality of points of reconstruction in a region of interest within a same horizontal plane, for a plurality of horizontal planes defined by a corresponding plurality of z-coordinates to generate a plurality of reconstructed image slices; and

generating a CT volume by arranging said plurality of reconstructed image slices according to the corresponding z-coordinates.

12. The method of claim 9 , further comprising:

repeating the steps of applying redundancy weighting and applying the backprojection operator for a plurality of points of reconstruction in the CT image; and

generating the CT image by arranging said plurality of image data values according to said plurality of points of reconstruction.

13. The method of claim 9 , wherein the step of applying a Hubert filter comprises:

applying a modified Hilbert filter to said subtracted data.

14. The method of claim 9 , wherein the step of applying redundancy weighting comprises:

applying one of (1) Parker weighting, (2) generalized Parker (MHS) weighting, (3) over-scan (OS) weighting, (4) Noo weighting, (5) quasi cone-beam (Q3D) weighting, and (6) Tam window weighting to said filtered data.

15. The method of claim 9 , wherein the step of applying a Hilbert filter comprises:

applying one of (1) horizontal filtering, (2) tangential filtering, (3) rotated filtering, and (4) Katsevich filtering to the subtracted data.

16. A system for determining an image data value at a point of reconstruction in a computed tomography (CT) image of a scanned object, comprising:

a CT scanning unit configured to generate projection data of the scanned object, the CT scanning unit including an X-ray source configured to generate X-rays and a detector having detector elements configured to produce the projection data of the scanned object; and

a processor, including:

a filtering unit configured to apply a ramp filter and a Hilbert filter to the projection data generated by the CT scanning unit to generate filtered data; and

a backprojecting unit configured to apply a backprojection operator with inverse distance weight to the filtered data generated by the filtering unit to generate the image data value at the point of reconstruction,

wherein the processor further comprises:

a projection subtraction unit configured to apply projection subtraction to the projection data generated by the CT scanning unit to generate subtracted data;

a Hilbert filtering unit configured to apply the Hilbert filter to the subtracted data generated by the projection subtraction unit to generate Hilbert-filtered data;

a projection addition unit configured to apply projection addition to (1) the Hilbert-filtered data generated by the Hilbert-filtering unit, and (2) ramp-filtered data generated by the filtering unit, to generate the filtered data; and

a weighting unit configured to apply redundancy weighting to the filtered data generated by the projection addition unit to generate weighted data,

wherein the backprojecting unit is configured to apply a backprojection operator with inverse distance weight to the weighted data generated by the weighting unit.

17. The system of claim 16 , wherein the CT scanning unit is configured to produce two-dimensional projections and the backprojecting unit is configured to apply the backprojection operator only to said filtered data contained within a Tam window.

18. The system of claim 16 , wherein the Hilbert filtering unit is configured to apply a

modified Hubert filter to the subtracted data generated by the projection subtraction unit.

19. The system of claim 16 , wherein the weighting unit is configured to apply one of (1) Parker weighting, (2) generalized Parker (MHS) weighting, (3) over-scan (OS) weighting, (4) Noo weighting, (5) quasi cone-beam (Q3D) weighting, and (6) Tam window weighting to the filtered data generated by the projection addition unit.

20. The system of claim 16 , wherein the filtering unit is configured to apply a modified ramp filter to the projection data generated by the CT scanning unit.

21. The system of claim 16 , wherein the filtering unit is configured to apply a modified ramp filter with an offset to the projection data generated by the CT scanning unit.

22. The system of claim 16 , wherein the CT scanning unit is configured to generate

projection data using one of a circular source trajectory, a helical source trajectory, and a saddle trajectory.

23. The system of claim 16 , wherein the scanning unit is configured to generate the projection data using a reconstruction range that satisfies Λ≧π+2 arcsin (r FOV /R), wherein Λ is the projection range, r FOV is a radial measurement of a field of view (FOV), and R is a radial measurement of a source trajectory.

24. A computer-readable medium having embedded therein a computer program product that includes instructions for execution on a computer system, which when executed by the computer system, causes the computer system to determine an image data value at a point of reconstruction in a computed tomography (CT) image of a scanned object by performing the steps of:

obtaining projection data of the scanned object;

filtering the obtained projection data with both a one-dimensional ramp filter and a Hilbert filter to generate filtered data;

applying a backprojection operator with inverse distance weighting to said filtered data to generate the image data value at the point of reconstruction in the CT image; and

displaying the generated image data value, wherein the filtering step comprises

applying projection subtraction to the obtained projection data to generate subtracted data;

applying the Hilbert filter to the subtracted data to generate Hilbert-filtered data; and

applying projection addition to the Hilbert-filtered data and ramp-filtered data to generate the filtered data, the ramp-filtered data being generated by filtering the obtained projection data with the one-dimensional ramp filter, and

wherein the step of obtaining projection data produces two-dimensional projections and the step of applying the backprojection operator is applied only to said filtered data contained within a Tam window.

25. The computer-readable medium of claim 24 , the computer program product further comprising:

repeating said applying step for a plurality of points of reconstruction in a medical image to obtain a corresponding plurality of image data values; and

generating the CT image by arranging said plurality of image data values according to said plurality of points of reconstruction.

26. The computer-readable medium of claim 24 , the computer program product further comprising:

repeating the step of applying the backprojection operator for a plurality of points of reconstruction in a volume of interest to obtain a plurality of image data values; and

generating a CT volume by arranging said plurality of image data values according to said plurality of points of reconstruction in the volume of interest.

27. The computer-readable medium of claim 24 , wherein the filtering step comprises:

filtering said projection data with a modified ramp filter.

28. The computer-readable medium claim 24 , wherein the filtering step comprises:

filtering said projection data with a modified ramp filter with an offset.

29. The computer-readable medium of claim 24 , wherein the obtaining step comprises:

obtaining the projection data using a CT system having one of a circular source trajectory, a helical source trajectory, and a saddle source trajectory.

30. The computer-readable medium of claim 24 , wherein the filtering step comprises:

filtering the obtained projection data using one of (1) horizontal filtering, (2) tangential filtering, (3) rotated filtering, and (4) Katsevich filtering.

31. The computer-readable medium of claim 24 , wherein the obtaining step comprises:

obtaining the projection data using a reconstruction range that satisfies Λ≧π+2 arcsin (r FOV /R), wherein Λ is the projection range, r FOV is a radial measurement of a field of view (FOV), and R is a radial measurement of a source trajectory.

32. A computer-readable medium having embedded therein a computer program product that includes instructions for execution on a computer system, which when executed by the computer system, causes the computer system to determine an image data value at a point of reconstruction in a computed tomography (CT) image of a scanned object by performing the steps of:

obtaining projection data of the scanned object;

filtering the obtained projection data with both a one-dimensional ramp filter and a Hilbert filter to generate filtered data;

applying a backprojection operator with inverse distance weighting to said filtered data to generate the image data value at the point of reconstruction in the CT image;

displaying the generated image data value, wherein the filtering step comprises

applying projection subtraction to the obtained projection data to generate subtracted data;

applying the Hilbert filter to the subtracted data to generate Hilbert-filtered data; and

applying projection addition to the Hilbert-filtered data and ramp-filtered data to generate the filtered data, the ramp-filtered data being generated by filtering the obtained projection data with the one-dimensional ramp filter, the steps further including

applying redundancy weighting to said filtered data to generate weighted data, wherein the step of applying the backprojection operator is applied to said weighted data to generate the image data value at the point of reconstruction in the CT image.

33. The computer-readable medium of claim 32 , the computer program product further comprising:

repeating said step of applying the backprojection operator for a plurality of points of reconstruction in a region of interest within a same horizontal plane as the point of reconstruction to obtain a plurality of image data values; and

generating the CT image by arranging said plurality of image data values according to said plurality of points of reconstruction.

34. The computer-readable medium of claim 33 , the computer program product further comprising:

repeating said steps of (1) applying redundancy weighting, and (2) repeating said step of applying the backprojection operator for a plurality of points of reconstruction in a region of interest within a same horizontal plane, for a plurality of horizontal planes defined by a corresponding plurality of z-coordinates to generate a plurality of reconstructed image slices; and

generating a CT volume by arranging said plurality of reconstructed image slices according to the corresponding z-coordinates.

35. The computer-readable medium of claim 32 , the computer program product further comprising:

repeating the steps of applying redundancy weighting and applying the backprojection operator for a plurality of points of reconstruction in the CT image; and

generating the CT image by arranging said plurality of image data values according to said plurality of points of reconstruction.

36. The computer-readable medium of claim 32 , wherein the step of applying a Hilbert filter comprises:

applying a modified Hilbert filter to said subtracted data.

37. The computer-readable medium product of claim 32 , wherein the step of applying redundancy weighting comprises:

applying one of (1) Parker weighting, (2) generalized Parker (MHS) weighting, (3) over-scan (OS) weighting, (4) Noo weighting, (5) quasi cone-beam (Q3D) weighting, and (6) Tam window weighting to said filtering data.

38. The computer-readable medium of claim 32 , wherein the step of applying a Hilbert filter comprises:

applying one of (1) horizontal filtering, (2) tangential filtering, (3) rotated filtering, and (4) Katsevich filtering to the subtracted data.