Registration of 4

1. A method for determining, for a fourth-generation computed tomography (CT) scanner, a positional offset of a center of a ring of fixed energy-discriminating detectors with respect to an iso-center of a third-generation X-ray source/detector system, the method comprising:

obtaining a plurality of offset images, each offset image being obtained from a scan executed with the ring of fixed energy-discriminating detectors positioned in a known offset location with respect to the iso-center of the third-generation X-ray source/detector system;

performing a current scan executed with the ring of fixed energy-discriminating detectors positioned in an unknown offset location with respect to the iso-center of the third-generation X-ray source/detector system, to obtain a current image;

calculating, for each offset image, a corresponding error value between the offset image and the current image to obtain a plurality of error values;

determining a smallest error value of the plurality of error values; and

determining the positional offset of the center of the ring of fixed energy-discriminating detectors to be an offset location corresponding to an offset image, of the plurality of offset images, having the determined smallest error value.

2. The method of claim 1 , wherein the obtaining step comprises obtaining the offset images from a database of offset images, each offset image being generated by an air scan or a scan of a known phantom.

3. The method of claim 1 , wherein the calculating step comprises:

calculating, for each offset image, a mean-squared error between pixels in the current image and pixels in the offset image.

4. The method of claim 1 , wherein the obtaining step comprises obtaining the plurality of offset images so that the plurality of offset images include images generated when the ring of fixed energy-discriminating detectors is positioned at various known offset positions around the iso-center of the third-generation X-ray source/detector system.

5. The method of claim 1 , wherein the known offset positions are arranged in a two-dimensional grid centered at the iso-center of the third-generation X-ray source/detector system.

6. A method for determining, for a fourth-generation computed tomography (CT) scanner, a positional offset of a center of a ring of fixed energy-discriminating detectors with respect to an iso-center of a third-generation X-ray source/detector system, the method comprising:

obtaining a plurality of offset images, each offset image being obtained from a scan executed with the ring of fixed energy-discriminating detectors positioned in a known offset location with respect to the iso-center of the third-generation X-ray source/detector system;

performing a current scan executed with the ring of fixed energy-discriminating detectors positioned in an unknown offset location with respect to the iso-center of the third-generation X-ray source/detector system, to obtain a current image;

calculating, for each offset image, a corresponding correlation value between the offset image and the current image to obtain a plurality of error values;

determining a largest correlation value of the plurality of correlation values; and

determining the positional offset of the center of the ring of fixed energy-discriminating detectors to be an offset location corresponding to an offset image, of the plurality of offset images, having the determined largest correlation value.

7. The method of claim 6 , wherein the obtaining step comprises obtaining the offset images from a database of offset images, each offset image being generated by an air scan or a scan of a known phantom.

8. The method of claim 6 , wherein the obtaining step comprises obtaining the plurality of offset images so that the plurality of offset images include images generated when the ring of fixed energy-discriminating detectors is positioned at various known offset positions around the iso-center of the third-generation X-ray source/detector system.

9. The method of claim 6 , wherein the known offset positions are arranged in a two-dimensional grid centered at the iso-center of the third-generation X-ray source/detector system.

10. An apparatus for determining, in a fourth-generation computed tomography (CT) scanner, a positional offset of a center of a ring of fixed energy-discriminating detectors with respect to an iso-center of a third-generation X-ray source/detector system, the apparatus comprising:

a processing circuit configured to execute a program that causes the processing circuit to

obtain a plurality of offset images, each offset image being obtained from a scan executed with the ring of fixed energy-discriminating detectors positioned in a known offset location with respect to the iso-center of the third-generation X-ray source/detector system;

perform a current scan executed with the ring of fixed energy-discriminating detectors positioned in an unknown offset location with respect to the iso-center of the third-generation X-ray source/detector system, to obtain a current image;

calculate, for each offset image, a corresponding error value between the offset image and the current image to obtain a plurality of error values;

determine a smallest error value of the plurality of error values; and

determine the positional offset of the center of the ring of fixed energy-discriminating detectors to be an offset location corresponding to an offset image, of the plurality of offset images, having the determined smallest error value.

11. The apparatus of claim 10 , further comprising:

a memory that stores the plurality of offset images, each offset image being stored in association with a corresponding offset location of the offset image.

12. An apparatus for determining, for a fourth-generation computed tomography (CT) scanner, a positional offset of a center of a ring of fixed energy-discriminating detectors with respect to an iso-center of a third-generation X-ray source/detector system, the apparatus comprising:

a processing circuit configured to execute a program that causes the processing circuit to

obtain a plurality of offset images, each offset image being obtained from a scan executed with the ring of fixed energy-discriminating detectors positioned in a known offset location with respect to the iso-center of the third-generation X-ray source/detector system;

perform a current scan executed with the ring of fixed energy-discriminating detectors positioned in an unknown offset location with respect to the iso-center of the third-generation X-ray source/detector system, to obtain a current image;

calculate, for each offset image, a corresponding correlation value between the offset image and the current image to obtain a plurality of error values;

determine a largest correlation value of the plurality of correlation values; and

determine the positional offset of the center of the ring of fixed energy-discriminating detectors to be an offset location corresponding to an offset image, of the plurality of offset images, having the determined largest correlation value.

13. The apparatus of claim 12 , further comprising:

a memory that stores the plurality of offset images, each offset image being stored in association with a corresponding offset location of the offset image.