Methods and apparatus for CT calibration
A method for normalizing a calibration of a computed tomographic (CT) imaging apparatus having a plurality of detector rows includes utilizing a prestored, predetermined inversion matrix and CT numbers obtained from images of a phantom to determine normalized calibration vectors for each row of a plurality of detector rows, and storing the determined normalized calibration vectors for each row of the plurality of detector rows in a memory for use in subsequent image reconstructions.
1. A method for normalizing a calibration of a computed tomographic (CT) imaging apparatus having a plurality of detector rows, said method comprising:
utilizing a prestored, predetermined inversion matrix and CT numbers obtained from images of a phantom to determine normalized calibration vectors for each row of a plurality of detector rows, the normalized calibration vectors are based on a relative contribution of each of a plurality of projection data slices generated by the plurality of detector rows, the inversion matrix is determined from a difference matrix of CT numbers obtained from images reconstructed using the projection data and a scaled projection data of the same ROI;
storing the determined normalized calibration vectors for each row of the plurality of detector rows in a memory for use in subsequent image reconstructions; and
calibrating the CT imaging apparatus using the determined normalized calibration vectors.
2. A method in accordance with claim 1 wherein to obtain the CT numbers, said method comprises imaging a water phantom.
3. A method in accordance with claim 1 wherein said utilizing said CT numbers comprises averaging CT numbers in a region of interest (ROI) of the phantom.
4. A method in accordance with claim 3 further comprising determining a scaling factor for each detector row in accordance with the inversion matrix and the averaged CT numbers in the ROI.
5. A method in accordance with claim 1 wherein said images are 3D images.
6. A method in accordance with claim 1 further comprising generating an image of an object using the normalized calibration vectors.
7. A method in accordance with claim 6 wherein to obtain the CT numbers, said method comprises imaging a water phantom.
8. A method in accordance with claim 6 wherein said images are 3D images.
9. A computed tomographic (CT) imaging apparatus having a plurality of detector rows and memory containing a prestored, predetermined inversion matrix, and a computer configured to:
utilize the prestored, predetermined inversion matrix and CT numbers obtained from images of a phantom to determine normalized calibration vectors for each row of a plurality of detector rows, the normalized calibration vectors are based on a relative contribution of each of a plurality of projection data slices generated by the plurality of detector rows, the inversion matrix is determined from a difference matrix of CT numbers obtained from images reconstructed using the projection data and a scaled projection data of the same RIO; and
store the determined normalized calibration vectors for each row of the plurality of detector rows in a memory for use in subsequent image reconstructions.
10. An apparatus in accordance with claim 9 wherein further configured to average CT numbers in a region of interest (ROI) of the phantom.
11. An apparatus in accordance with claim 10 further configured to determine a scaling factor for each detector row in accordance with the inversion matrix and the averaged CT numbers in the ROI.
12. An apparatus in accordance with claim 9 wherein said images are 3D images.
13. An apparatus in accordance with claim 9 further configured to generate an image of an object using the normalized calibration vectors.
14. A computer program embodied on a computer readable medium, said computer program including at least one code segment configured to instruct a processor to normalize a calibration of a computed tomographic (CT) imaging apparatus having a plurality of detector rows by:
utilizing a prestored, predetermined inversion matrix and CT numbers obtained from images of a phantom to determine normalized calibration vectors for each row of a plurality of detector rows, the normalized calibration vectors are based on a relative contribution of each of a plurality of projection data slices generated by the plurality of detector rows, the inversion matrix is determined from a difference matrix of CT numbers obtained from images reconstructed using the projection data and a scaled projection data of the same ROI;
storing the determined normalized calibration vectors for each row of the plurality of detector rows in a memory for use in subsequent image reconstructions; and
calibrating the CT imaging apparatus using the determined normalized calibration vectors.
15. A computer program in accordance with claim 14 further comprising a code segment configured to instruct the processor to obtain the CT numbers by imaging a water phantom.
16. A computer program in accordance with claim 14 further comprising a code segment configured to instruct the processor to utilize said CT numbers by averaging CT numbers in a region of interest (ROI) of the phantom.
17. A computer program in accordance with claim 16 further comprising a code segment configured to instruct the processor to determine a scaling factor for each detector row in accordance with the inversion matrix and the averaged CT numbers in the ROI.
18. A computer program in accordance with claim 14 wherein said images are 3D images.
19. A computer program in accordance with claim 14 further comprising a code segment configured to instruct the processor to generate an image of an object using the normalized calibration vectors.
20. A computer program in accordance with claim 19 further comprising a code segment configured to instruct the processor to obtain the CT numbers by imaging a water phantom with 3D images.