METHOD AND SYSTEM OF CT DATA CORRECTION

• US 20060109950A1
• Filed: 11/24/2004
• Published: 05/25/2006
• Est. Priority Date: 11/24/2004
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Ruimi, David, Wu, Xiaoye, Basu, Samit, Meirav, Oded, Drapkin, Evgeny, De Man, Bruno, Arenson, Jerome S., Samsonov, Dmitry, Greenberg, Lev, Tkaczyk, John, Du, Yangeng
• Granted Patent: US 7,382,853 B2
• Time in Patent Office: Days
• US Class Current: 378/4
• CPC Class Codes: A61B 6/027 characterised by the use of a particular data acquisition trajectory, e.g. helical or spiral
• CPC Class Codes: A61B 6/032 Transmission computed tomography [CT]
• CPC Class Codes: A61B 6/4241 using energy resolving detectors, e.g. photon counting
• CPC Class Codes: A61B 6/482 involving multiple energy imaging
• CPC Class Codes: A61B 6/583 using calibration phantoms
• CPC Class Codes: G01T 1/1644 using an array of optically separate scintillation elements permitting direct location of scintillations G01T1/1645 takes precedence
• CPC Class Codes: G01T 1/1647 Processing of scintigraphic data not related to a particular imaging system G01T1/2992
• CPC Class Codes: G06T 2207/10081 Computed x-ray tomography [CT]
• CPC Class Codes: G06T 2207/30004 Biomedical image processing
• CPC Class Codes: G06T 2207/30112 Baggage; Luggage; Suitcase
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06T 5/70 Denoising; Smoothing
• CPC Class Codes: Y10S 378/901 Computer tomography program or processor

Abstract

An adaptive CT data acquisition system and technique is presented whereby radiation emitted for CT data acquisition is dynamically controlled to limit exposure to those detectors of a CT detector assembly that may be particularly susceptible to saturation during a given data acquisition. The data acquisition technique recognizes that for a given subject size and position that pre-subject filtering and collimating of a radiation beam may be insufficient to completely prevent detector saturation. Therefore, the present invention includes implementation of a number of CT data correction techniques for correcting otherwise unusable data of a saturated CT detector. These data correction techniques include a nearest neighbor correction, off-centered phantom correction, off-centered synthetic data correction, scout data correction, planar radiogram correction, and a number of others. The invention is applicable with energy discriminating CT systems as well as with conventional CT systems and other multi-energy CT systems, such as dual kVp-based systems.

Claims

1. A scanner comprising:

a radiation source;

a radiation detector assembly having a plurality of radiation detectors; and

a computer operationally connected to the radiation detector assembly and programmed to correct an output of an over-ranging detector with output of a non-over-ranging detector.

2. The scanner of claim 1 wherein the computer is further programmed to correct the output of an over-ranging detector with the output of a non-over-ranging detector that is adjacent to the over-ranging detector.

3. The scanner of claim 2 wherein the computer is further programmed to:

generate a dataset that is a replicate of the output of the non-over-ranging detector;

generate a mirrored dataset having data that is a mirror of the dataset;

effectuate a sign change of each data element of the mirrored dataset to yield a sign-changed dataset; and

then

append the sign-changed dataset to the output of the non-over-ranging detector.

4. The scanner of claim 3 wherein the computer is further programmed to clip the sign-changed dataset after being appended to the output of the non-over-ranging detector such that data below a threshold is not used for image reconstruction.

5. The scanner of claim 1 wherein the computer is further programmed to carry out a scout scan and correct the output of an over-ranging detector with non-over-ranging output of that detector generated during the scout scan.

6. The scanner of claim 5 wherein the scout scan includes at least one of an AP scan and a lateral scan.

7. The scanner of claim 5 wherein the scout scan is a planar scout scan.

8. The scanner of claim 5 wherein the computer is further programmed to carry out the scout scan at a dose level insufficient to cause over-ranging of a detector.

9. The scanner of claim 5 wherein the computer is further programmed to match views acquired during the scout scan to views acquired during one of an axial and a helical imaging scan.

10. The scanner of claim 9 wherein the computer is further programmed to correct a saturated view of an imaging scan with a view of the scout scan.

21. The method of claim 1 further comprising the step of determining a center of mass of the object from scout data acquired from the object.

22. The method of claim 21 further comprising the step of carrying out a lateral scout and an AP scout to acquire object size and position information.

11. A method of CT data correction comprising the steps of:

acquiring CT data from an object;

comparing a profile of the CT data to an off-centered phantom or synthetic data profile; and

correcting saturated portions of the CT data from the off-centered phantom or synthetic data profile.

12. The method of claim 11 wherein the off-centered phantom profile includes an off-centered water or synthetic water data profile.

13. The method of claim 11 wherein the off-centered phantom profile includes an off-centered cylindrical object or synthetic cylindrical object profile.

14. The method of claim 11 wherein the off-centered phantom profile includes an off-centered elliptical object or synthetic elliptical object profile.

15. The method of claim 11 further comprising the step of approximating an object shape and position and selecting the off-centered phantom profile from a number of off-centered phantom profiles from the object shape and position or generating the off-centered synthetic data profile from the object shape and position.

16. The method of claim 15 further comprising the steps of:

estimating a line-fit to a last set of non-saturated values of CT data;

determining a slope and a line intercept of the line-fit; and

determining the off-centered phantom or synthetic data profile that should be selected for correcting saturated portions of the CT data from the slope and the line intercept.

17. The method of claim 15 further comprising the steps of determining a radius of curvature of an edge of the object from which the CT dater is acquired and, form the radius of curvature, determining an extrapolation radius.

18. The method of claim 17 further comprising the step of selecting the off-centered phantom profile from a number of off-centered phantom profiles or generating the synthetic data profile based on the extrapolation radius.

19. The method of claim 16 further comprising the step of:

generating a sinogram from the CT data;

identifying an edge of the sinogram;

determining a degree of curvature at the edge; and

from the degree of curvature, determining a radius of curvature of the edge of the object from which the CT data is acquired.

20. The method of claim 19 further comprising the steps of:

determining an initial curvature at the edge;

determining a final curvature at the edge;

determining an average of the initial curvature and the final curvature; and

determining the radius of curvature of the edge from the average.

23. A computer readable storage medium having a computer program stored thereon and representing a set of instructions that when executed by a computer causes the computer to:

normalize signal values for each detector element of a CT detector;

compare a signal value for a detector element to a pair of thresholds;

characterize a CT view corresponding to the signal value of a given detector as one of a normal view, a noisy view, and a saturated view from the comparison;

apply a filter kernel to the CT view if the CT view is characterized as a noisy view; and

apply a saturated view correction to the CT view if the CT view is characterized as a saturated view.

24. The computer readable storage medium of claim 23 wherein the computer is further caused to set a strength and range of the filter kernel based on the signal value of the noisy CT view.

25. The computer readable storage medium of claim 24 wherein the computer is further caused to replace a corrupted CT view with data from one or more non-corrupted CT views proximate the corrupted CT view.

26. The computer readable storage medium of claim 25 wherein the computer is further caused to determine an average signal strength of a set of detectors neighboring the given detector and replace the corrupted CT view with the average signal strength.

27. A method of CT data correction comprising the steps of:

(A) air-correcting saturated views of a set of CT views;

(B) generating an air-corrected sinogram from the set of CT views;

(C) reconstructing an image from the set of CT views;

(D) reprojecting the image to generate another set of CT views;

(E) generating a reprojected sinogram from the another set of CT views;

(F) comparing the reprojected sinogram to a saturated view sinogram mask;

(G) updating the air-corrected sinogram based on the comparison; and

(H) reconstructing an image from the updated air-corrected sinogram.

28. A method of CT data correction comprising the steps of:

filtering without backprojecting corrected CT views;

determining a measure of flatness of the filtered CT views;

determining a value of correction for a corrected CT view; and

re-correcting the corrected CT view based on the value of correction.

29. A method of CT data correction comprising the steps of:

acquiring view data from either axial, helical or scout scans;

verifying that no data saturation is present in a view;

computing a nominal integral value of a preprocessed signal over the view;

comparing the nominal integral value to an integral value of saturation corrected views; and

re-correcting the saturation corrected views based on the comparison.