Methods and apparatus for cardiac scoring with a multi-beam scanner

• US 6,226,350 B1
• Filed: 03/03/1999
• Issued: 05/01/2001
• Est. Priority Date: 12/31/1998
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Hsieh, Jiang
• Primary Examiner(s): BRUCE, DAVID VERNON
• Application Number:
  US09/261,778
• Time in Patent Office: 790 Days
• Field of Search: 378/98, 378/98.2, 378/98.11, 378/98.12
• US Class Current: 378/98
• CPC Class Codes: A61B 5/352 Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval
• CPC Class Codes: A61B 6/032 Transmission computed tomography [CT]
• CPC Class Codes: A61B 6/541 involving acquisition triggered by a physiological signal

Abstract

The present invention, in one form, includes an imaging system having a x-ray source and detector array and a reconstruction algorithm. The algorithm removes overlapping structures from a patient scan so that enhanced images representing a moving heart are generated. More specifically and in one embodiment, an estimated background representing the overlapping structures is determined using the projection data. The estimated background is then subtracted from the projection data to generate filtered data. The filtered data is then used to generate an enhanced image so that cardiac calcification may be identified.

Claims

1. A method for generating an image of an object using an imaging system, the object having stationary structures and at least one moving structure, the imaging system including at least one x-ray source and at least one x-ray detector array, said method comprising the steps of:

collecting projection data using each detector array;

determining an average difference of the projection data; and

filtering the projection data to remove the stationary objects using the determined average difference of the projection data.

2. A method in accordance with claim 1 further comprising the step of generating at least one enhanced image of the object using the filtered projection data.

3. A method in accordance with claim 2 wherein filtering the projection data to remove the stationary objects comprises the steps of:

utilizing the determined average difference of projection data to generate estimated background data; and

subtracting the estimated background data from the projection data.

4. A method in accordance with claim 3 wherein subtracting the estimated background data from the projection data comprises the step of subtracting average data from each frame of projection data.

5. A method in accordance with claim 3 wherein each frame of projection data includes a plurality of pixels, and wherein generating estimated background data comprises the step of:

determining an average intensity of each pixel in accordance with;

$\mathrm{Average}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{Intensity}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{of}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{Pixel}<br><br>\left(i,j\right)=\frac{\underset{k=1}{\overset{N}{\sum <br><br>}}<br><br>S_k<br><br>\left(i,j\right)}{N}.<br><br>\begin{array}{c}\begin{array}{c}\mathrm{where};<br><br>\\ N=a<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{number}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{of}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{frames}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{of}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{projection}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{data},\mathrm{and}\end{array}\\ S_k<br><br>\left(i,j\right)=\mathrm{intensity}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{of}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{pixel}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(i,j\right)<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{of}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{the}<br><br>\text{\hspace{1em}<br><br>}<br><br>k_{\mathrm{th}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{frame}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{of}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{projection}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{data}.\end{array}$

6. A method in accordance with claim 1 wherein collecting projection data comprises the step of collecting at least two frames of projection data.

7. A method in accordance with claim 6 wherein determining an average difference of the projection data comprises the steps of:

determining difference data between a first frame of projection data and at least a second frame of projection data; and

determining a difference data average.

8. A method in accordance with claim 7 wherein filtering the projection data to remove the stationary objects comprises the step of

identifying a selected portion of projection frames using the difference data average.

9. A method in accordance with claim 8 further comprising the steps of:

removing the selected portion of projection frames from the projection data to generate filtered projection data; and

generating an image of the object using the filtered projection data.

10. A method in accordance with claim 8 further comprising the steps of:

assigning a first weight to the selected portion of projection frames;

assigning a second weight to non-selected portion of projection frames; and

generating an image of the object using the using the weighted projection frames.

11. A method in accordance with claim 10 further comprising the step of identifying a motion phase of the moving structure.

12. A method in accordance with claim 11 wherein the first weight and the second weight are each a function of the motion phase of the moving structure.

13. A method in accordance with claim 6 wherein the system further includes an ECG signal representative of a cardiac cycle of the heart, and wherein filtering the projection data to remove the stationary objects comprises the step of identifying a selected portion of projection frames using the ECG signal.

14. A method for generating an image of an object using an imaging system including a first x-ray source, a first detector array, a second x-ray source, and a second detector array comprises the steps of:

collecting at least two frames of first projection data using the first detector array wherein the first x-ray source and first detector array aligned along a first angle relative to the object;

collecting at least two frames of second projection data using the second detector array, wherein the second x-ray source and the second detector array aligned along a second angle relative to the object;

determining an average difference of the at least two frames of first projection data;

determining an average difference of the at least two frames of second projection data; and

filtering the first projection data and the second projection data to remove the stationary objects using the respective determined average differences of the first projection data and the second projection data.

15. A method in accordance with claim 14 wherein the first angle is not equal to the second angle, and wherein said method further comprises the step of synchronizing the first projection data and the second projection data.

16. A method in accordance with claim 14 further comprising the step of performing a frame to frame registration of each respective frame of the first projection data and the second projection data.

17. An imaging system for generating an image of an object, the object having stationary structures and at least one moving structure, said imaging system including at least one x-ray source and at least one x-ray detector array and configured to:

collect projection data using each said detector array;

determine an average difference of the projection data; and

filter the projection data to remove the stationary objects using the determined average difference of the projection data.

18. An imaging system in accordance with claim 17 further configured to generate at least one enhanced image of the object using the filtered projection data.

19. An imaging system in accordance with claim 18 wherein to filter the projection data to remove the stationary objects, said system configured to:

utilize said determined average difference of projection data to generate estimated background data; and

subtract the estimated background data from the projection data.

20. An imaging system in accordance with claim 19 wherein to subtract the estimated background data from the projection data, said system configured to subtract the average data from each frame of projection data.

21. An imaging system in accordance with claim 19 wherein each frame of projection data includes a plurality of pixels, and wherein to generate estimated background data using the projection data, said system configured to determine an average intensity of each pixel in accordance with:

$\mathrm{Average}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{Intensity}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{of}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{Pixel}<br><br>\left(i,j\right)=\frac{\underset{k=1}{\overset{N}{\sum <br><br>}}<br><br>S_k<br><br>\left(i,j\right)}{N}.<br><br>\begin{array}{c}\begin{array}{c}\mathrm{where};<br><br>\\ N=a<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{number}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{of}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{frames}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{of}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{projection}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{data},\mathrm{and}\end{array}\\ S_k<br><br>\left(i,j\right)=\mathrm{intensity}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{of}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{pixel}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(i,j\right)<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{of}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{the}<br><br>\text{\hspace{1em}<br><br>}<br><br>k_{\mathrm{th}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{frame}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{of}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{projection}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{data}.\end{array}$

22. An imaging system in accordance with claim 17 wherein to collect projection data, said system configured to collect at least two frames of projection data.

23. An imaging system in accordance with claim 22 wherein to determine an average difference of the projection data, said system configured to:

determine difference data between a first frame of projection data and at least a second frame of projection data; and

determine a difference data average.

24. An imaging system in accordance with claim 23 wherein to filter the projection data to remove the stationary objects, said system configured to

identify a selected portion of projection frames using the difference data average.

25. An imaging system in accordance with claim 24 further configured to:

remove the selected portion of projection frames from the projection data to generate filtered projection data; and

generate an image of the object using the filtered projection data.

26. An imaging system in accordance with claim 24 further configured to:

assign a first weight to the selected portion of projection frames;

assign a second weight to non-selected portion of projection frames; and

generate an image of the object using the using the weighted projection frames.

27. An imaging system in accordance with claim 26 further configured to identify a motion phase of the moving structure.

28. An imaging system in accordance with claim 27 wherein said first weight and said second weight are each a function of said motion phase of the moving structure.

29. An imaging system in accordance with claim 22 wherein said system further includes an ECG signal representative of a cardiac cycle of the heart, and wherein to filter the projection data to remove the stationary objects, said system configured to identify a selected portion of projection frames using said ECG signal.

30. An imaging system for generating an image of an object, the object having stationary structures and at least one moving structure, said imaging system comprising a first x-ray source, a first detector array, a second x-ray source, and a second detector array, said system configured to:

collect at least two frames of first projection data using said first detector array wherein said first x-ray source and said first detector array aligned along a first angle relative to the object;

collect at least two frames of second projection data using said second detector array, wherein said second x-ray source and said second detector array aligned along a second angle relative to the object;

determine an average difference of said at least two frames of first projection data;

determine an average difference of said at least two frames of second projection data; and

filter said first projection data and said second projection data to remove the stationary objects using the respective said determined average differences of said first projection data said second projection data.

31. An imaging system in accordance with claim 30 wherein said first angle is not equal to said second angle, and wherein said system further configured to synchronize the first projection data and the second projection data.