METHOD AND SYSTEM OF CT DATA CORRECTION

• US 20070116170A1
• Filed: 01/25/2007
• Published: 05/24/2007
• Est. Priority Date: 11/24/2004
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Basu, Samit, De Man, Bruno
• Granted Patent: US 7,283,604 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 CT imaging system comprising:

a rotatable gantry having an opening therein to receive a subject to be scanned;

an x-ray source disposed within the rotatable gantry and configured to project a fan beam of x-rays at the subject during CT data acquisition; and

a computer programmed to;

acquire CT data from an object in a plurality of detector elements; and

(A) identify saturated views from the CT data;

(B) generate an air-corrected sinogram in the saturated views; and

(C) reconstruct an image from the air-corrected sinogram.

2. The CT imaging system of claim 1 wherein the computer is further programmed to:

(D) generate a saturated data mask from the air-corrected sinogram;

(E) reproject the image to generate another set of CT data;

(F) generate a reprojected sinogram from the another set of CT data;

(G) compare the reprojected sinogram to the saturated data mask;

(H) determine from the comparison a standard deviation between the reprojected sinogram and the air-corrected sinogram; and

(I) determine whether the standard deviation has converged to within a minimum standard deviation.

3. The CT imaging system of claim 2 wherein, if the standard deviation of step (I) has not converged, the computer is further programmed to:

(J) update the air-corrected sinogram based on the comparison; and

(K) repeat steps (D)-(J) until convergence occurs at step (I).

4. The CT imaging system of claim 1 wherein the computer determines if the CT data is noisy, and if so, applies a filter kernel to the noisy CT data.

5. The CT imaging system of claim 4 wherein the computer sets a strength and range of the filter kernel based on the signal value of the noisy CT data, and replaces the noisy CT data with normal CT data acquired proximate the noisy data.

6. The CT imaging system of claim 1 wherein the CT data acquired is from one of a conventional CT or a multi-energy CT system.

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

acquiring CT data from an object in a plurality of detector elements, the CT data being comprised of at least one of normal data, noisy data, and saturated data; and

correcting any saturated CT data detector elements using at least the steps of;

(A) identifying saturated views of a set of CT views;

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

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

8. The method of claim 7 wherein the step of correcting the saturated CT data further comprises the steps of:

(D) generating a saturated data mask from the air-corrected sinogram;

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

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

(G) comparing the reprojected sinogram to the saturated data mask;

(H) determining from the comparison a standard deviation between the reprojected sinogram and the air-corrected sinogram; and

(I) determining whether the standard deviation has converged to within a minimum standard deviation.

9. The method of claim 8 wherein, if the standard deviation of step (I) has not converged, the method further comprises the steps of:

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

(K) repeat steps (D)-(J) until convergence occurs at step (I).

10. The method of claim 9 further comprising the step of applying a filter kernel to the CT data if the CT data is characterized as noisy.

11. The method of claim 10 wherein the step of applying a filter kernel further comprises setting a strength and range of the filter kernel based on the signal value of the noisy CT data, and replacing the noisy CT data with non-noisy CT data acquired proximate the noisy data.

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

acquire CT data from an object in a plurality of detector elements;

characterize the CT data in each of the detector elements as one of normal data, noisy data, and saturated data; and

correct the saturated CT data detector elements wherein the computer is further programmed to;

(A) identify saturated views from the CT data;

(B) generate an air-corrected sinogram in the saturated views; and

(C) reconstruct an image from the air-corrected sinogram.

13. The computer readable storage medium of claim 12 wherein the computer is further caused to:

(D) generate a saturated data mask from the air-corrected sinogram;

(E) reproject the image to generate another set of CT data;

(F) generate a reprojected sinogram from the another set of CT data;

(G) compare the reprojected sinogram to the saturated data mask;

(H) determine from the comparison a standard deviation between the reprojected sinogram and the air-corrected sinogram; and

(I) determine whether the standard deviation has converged to within a minimum standard deviation.

14. The computer readable storage medium of claim 13 wherein, if the standard deviation of step (I) has not converged, the computer is further programmed to:

(J) update the air-corrected sinogram based on the comparison; and

(K) repeat steps (D)-(J) until convergence occurs at step (I).

15. The computer readable storage medium of claim 12 wherein the computer is further caused to apply a filter kernel to the CT data if the CT data is characterized as noisy.

16. The computer readable storage medium of claim 15 wherein when the computer applies the filter kernel, the computer further sets a strength and range of the filter kernel based on the signal value of the noisy CT data, and replaces the noisy CT data with normal CT data acquired proximate the noisy data.

17. The computer readable storage medium of claim 12 wherein the CT data is data acquired from one of a conventional CT or a multi-energy CT system.