METHOD AND APPARATUS FOR OBJECT SCAN DATA CORRECTION IN A PHOTON COUNTING X-RAY IMAGING SYSTEM WITH AUTOMATIC EXPOSURE CONTROL

1 . A method for performing object scan data correction in an X-ray imaging system having a photon-counting detector, the X-ray imaging system including an X-ray tube for emitting X-rays, the method comprising:

acquiring calibration scan data from a calibration scan performed using a plurality of slabs;

performing function fitting based on the acquired calibration scan data to generate a plurality of fitting functions corresponding to the plurality of slabs, each corresponding fitting function representing a relationship between a counting measurement detected with respect to one slab of the plurality of slabs and a tube current applied to the X-ray tube;

establishing a calibration table based on the acquired calibration scan data;

acquiring object scan data from an object scan performed on an imaging object;

performing data correction for the acquired object scan data, based on the established calibration table and the generated plurality of fitting functions; and

reconstructing an image of the imaging object based on the performed data correction.

2 . The method of claim 1 , wherein the step of acquiring the calibration scan data further comprises acquiring the calibration scan data from the calibration scan performed using each slab of the plurality of slabs, with a first number (n 1 ) of tube currents applied to the X-ray tube,

the establishing step further comprises:

establishing, based on the acquired calibration scan data, the first number (n 1 ) of sub-calibration tables to form the established calibration table, each sub-calibration table corresponding to one tube current of the first number (n 1 ) of tube currents, and

storing the first number (n 1 ) of sub-calibrations tables, for use in performing the data correction,

the step of performing the data correction further comprises:

for each view of the acquired object scan data, projecting a counting measurement detected by each pixel of the photon-counting detector, based on the generated plurality of fitting functions, to a projected counting measurement, as if the projected counting measurement were detected when a specific tube current of the first number (n 1 ) of tube currents is applied to the X-ray tube, and

using the projected counting measurements to generate a line-integral sinogram, based on the first number (n 1 ) of sub-calibration tables, and

the reconstructing step further comprises reconstructing the image of the imaging object, based on the generated line-integral sinogram.

3 . The method of claim 2 , wherein the X-ray imaging system further comprises a tube current detector configured to directly or indirectly detect a tube current applied to the X-ray tube during the object scan, and

the projecting step further comprises:

for each view of the acquired object scan data, based on a counting measurement detected by each pixel of the photon-counting detector and a corresponding tube current detected when the view is acquired, using at least one fitting function of the generated plurality of fitted functions, to derive a corresponding fitting function with respect to an attenuation pathlength corresponding to the counting measurement, and

calculating, based on the derived corresponding fitting function, a counting measurement corresponding to one tube current of the first number (n 1 ) of tube currents that is closest to the corresponding tube current detected when the view is acquired, as the projected counting measurement.

4 . The method of claim 2 , wherein the step of performing function fitting further comprises performing the function fitting based on the acquired calibration scan data to generate a corresponding polynomial fitting function with respect to each slab of the plurality of slabs, and

a number of order of the corresponding polynomial fitting function is determined based on the first number (n 1 ).

5 . The method of claim 2 , wherein the step of generating the line-integral sinogram further comprises, generating a counting line-integral sinogram when the X-ray imaging system operates in a counting imaging mode, and generating a basis material line-integral sinogram when the X-ray imaging system operates in a material decomposition imaging mode, and

the step of performing function fitting further comprises, when the X-ray imaging system operates in the material decomposition imaging mode, for each slab of the plurality of slabs, generating respective fitting functions specific to individual energy bins.

6 . The method of claim 1 , wherein the step of acquiring the calibration scan data further comprises acquiring the calibration scan data from the calibration scan performed using each slab of the plurality of slabs, where the plurality of slabs have different attenuation pathlengths from one another, and

an attenuation pathlength step among the plurality of slabs is not larger than a predetermined threshold.

7 . The method of claim 1 , wherein the step of establishing the calibration table further comprises establishing, based on the acquired calibration scan data, a particular calibration table for calibrating a detector response of the X-ray imaging system and/or for correcting a pile-up effect of the X-ray imaging system.

8 . The method of claim 1 , wherein the step of acquiring the calibration scan data further comprises acquiring the calibration scan data from the calibration scan performed using each slab of the plurality of slabs, with a first number (n 1 ) of tube currents applied to the X-ray tube,

the establishing step further comprises,

calculating supplemental calibration data based on the generated plurality of fitting functions, as if the supplemental calibration data were acquired from a calibration scan performed on each slab of the plurality of slabs, with a second number (n 2 ) of tube currents applied to the X-ray tube, where the second number (n 2 ) of tube currents are different from the first number (n 1 ) of tube currents,

establishing, based on the acquired calibration scan data and the calculated supplemental calibration data, a third number (n 3 ) of sub-calibration tables to form the established calibration table, each sub-calibration table corresponding to one tube current of the first number (n 1 ) and second number (n 2 ) of tube currents, where n 3 =n 1 +n 2 , and

storing the third number (n 3 ) of sub-calibrations tables, for use in the data correction,

the step of performing the data correction for the acquired object scan data further comprising using the acquired object scan data to generate a line-integral sinogram, based on the third number (n 3 ) of sub-calibrations tables, and

the reconstructing step further comprises reconstructing the image of the imaging object, based on the generated line-integral sinogram.

9 . The method of claim 8 , wherein the step of calculating the supplemental calibration data further comprises, for each fitting function of the generated plurality of fitting functions, using the fitting function to calculate a counting measurement corresponding to each tube current of the second number (n 2 ) of tube currents,

the first number (n 1 ) and second number (n 2 ) of tube currents are distributed across a tube current range applied during the object scan, and

a tube current step among the first number (n 1 ) and second number (n 2 ) of tube currents is not larger than a predetermined threshold.

10 . An apparatus for performing object scan data correction in an X-ray imaging system having a photon-counting detector, the X-ray imaging system including an X-ray tube for emitting X-rays, the apparatus comprising:

processing circuitry configured to

acquire calibration scan data from a calibration scan performed using a plurality of slabs,

perform function fitting based on the acquired calibration scan data to generate a plurality of fitting functions corresponding to the plurality of slabs, each corresponding fitting function representing a relationship between a counting measurement detected with respect to one slab of the plurality of slabs and a tube current applied to the X-ray tube,

establish a calibration table based on the acquired calibration scan data,

acquire object scan data from an object scan performed on an imaging object,

perform data correction for the acquired object scan data, based on the established calibration table and the generated plurality of fitting functions, and

reconstruct an image of the imaging object based on the performed data correction.

11 . The apparatus of claim 10 , wherein the processing circuitry is further configured to:

acquire the calibration scan data from the calibration scan performed using each slab of the plurality of slabs, with a first number (n 1 ) of tube currents applied to the X-ray tube,

establish the calibration table by,

establishing, based on the acquired calibration scan data, the first number (n 1 ) of sub-calibration tables to form the established calibration table, each sub-calibration table corresponding to one tube current of the first number (n 1 ) of tube currents, and

storing the first number (n 1 ) of sub-calibrations tables, for use in performing the data correction,

perform the data correction by:

for each view of the acquired object scan data, projecting a counting measurement detected by each pixel of the photon-counting detector, based on the generated plurality of fitting functions, to a projected counting measurement, as if the projected counting measurement were detected when a specific tube current of the first number (n 1 ) of tube currents is applied to the X-ray tube, and

using the projected counting measurements to generate a line-integral sinogram, based on the first number (n 1 ) of sub-calibration tables, and

reconstruct the image of the imaging object, based on the generated line-integral sinogram.

12 . The apparatus of claim 11 , wherein the X-ray imaging system further comprises a tube current detector configured to directly or indirectly detect a tube current applied to the X-ray tube during the object scan, and

the processing circuitry is further configured to:

for each view of the acquired object scan data, based on a counting measurement detected by each pixel of the photon-counting detector and a corresponding tube current detected when the view is acquired, use at least one fitting function of the generated plurality of fitted functions, to derive a corresponding fitting function with respect to an attenuation pathlength corresponding to the counting measurement, and

calculate, based on the derived corresponding fitting function, a counting measurement corresponding to one tube current of the first number (n 1 ) of tube currents that is closest to the corresponding tube current detected when the view is acquired, as the projected counting measurement.

13 . The apparatus of claim 11 , wherein the processing circuitry is further configured to perform the function fitting based on the acquired calibration scan data to generate a corresponding polynomial fitting function for each slab of the plurality of slabs, and

a number of order of the corresponding polynomial fitting function is determined based on the first number (n 1 ).

14 . The apparatus of claim 11 , wherein the processing circuitry is further configured to:

generate a counting line-integral sinogram when the X-ray imaging system operates in a counting imaging mode, and generate a basis material line-integral sinogram when the X-ray imaging system operates in a material decomposition imaging mode, and

when the X-ray imaging system operates in the material decomposition imaging mode, for each slab of the plurality of slabs, generate respective fitting functions specific to individual energy bins.

15 . The apparatus of claim 10 , wherein the processing circuitry is further configured to acquire the calibration scan data from the calibration scan performed using each slab of the plurality of slabs, where the plurality of slabs have different attenuation pathlengths from one another, and

an attenuation pathlength step among the plurality of slabs is not larger than a predetermined threshold.

16 . The apparatus of claim 10 , wherein the processing circuitry is further configured to establish, based on the acquired calibration scan data, a particular calibration table for calibrating a detector response of the X-ray imaging system and/or for correcting a pile-up effect of the X-ray imaging system.

17 . The apparatus of claim 10 , wherein the processing circuitry is further configured to:

acquire the calibration scan data from the calibration scan performed using each slab of the plurality of slabs, with a first number (n 1 ) of tube currents applied to the X-ray tube,

establish the calibration table by

calculating supplemental calibration data based on the generated plurality of fitting functions, as if the supplemental calibration data were acquired from a calibration scan performed on each slab of the plurality of slabs, with a second number (n 2 ) of tube currents applied to the X-ray tube, where the second number (n 2 ) of tube currents are different from the first number (n 1 ) of tube currents,

establishing, based on the acquired calibration scan data and the calculated supplemental calibration data, a third number (n 3 ) of sub-calibration tables to form the established calibration table, each sub-calibration table corresponding to one tube current of the first number (n 1 ) and second number (n 2 ) of tube currents, where n 3 =n 1 +n 2 , and

storing the third number (n 3 ) of sub-calibrations tables, for use in the data correction,

use the acquired object scan data to generate a line-integral sinogram, based on the third number (n 3 ) of calibrations tables, and

reconstruct the image of the imaging object, based on the generated line-integral sinogram.

18 . The apparatus of claim 17 , wherein the processing circuitry is further configured to, for each fitting function of the generated plurality of fitting functions, use the fitting function to calculate a counting measurement corresponding to each tube current of the second number (n 2 ) of tube currents,

wherein the first number (n 1 ) and second number (n 2 ) of tube currents are distributed across a tube current range applied during the object scan, and

a tube current step among the first number (n 1 ) and second number (n 2 ) of tube currents is not larger than a predetermined threshold.

19 . A method for performing object scan data correction in an X-ray imaging system having a photon-counting detector, the X-ray imaging system including an X-ray tube for emitting X-rays, the method comprising:

acquiring calibration scan data from a calibration scan performed using each slab of a plurality of slabs, with a first number (n 1 ) of tube currents applied to the X-ray tube;

establishing, based on the acquired calibration scan data, the first number (n 1 ) of calibration tables to be used in data correction, each calibration table of the first number (n 1 ) of calibration tables corresponding to one tube current of the first number (n 1 ) of tube currents;

calculating, for a second number (n 2 ) of tube currents, the second number (n 2 ) of calibration tables based on the first number (n 1 ) of calibration tables, where the second number (n 2 ) of tube currents are different from the first number (n 1 ) of tube currents;

acquiring object scan data from an object scan performed on an imaging object;

performing the data correction for the acquired object scan data, based on the first number (n 1 ) and second number (n 2 ) of calibration tables; and

reconstructing an image of the imaging object based on the performed data correction.

20 . The method of claim 19 , wherein the calculating step further comprises, for each specific tube current of the second number (n 2 ) of tube currents, selecting, from the first number (n 1 ) of calibration tables, two or more calibration tables corresponding to tube currents closest to the specific tube current, and

performing interpolation on the selected two or more calibration tables to derive a calibration table for the specific tube current.