X-ray computed tomography apparatus and photon counting method
According to embodiment, an X-ray computed tomography apparatus includes an X-ray tube, an X-ray detector including a scintillator generating scintillation light upon incidence of X-ray photons and a photodetection element, a peak value detector detecting peak values corresponding to X-ray photons based on an output signal from the element, processing circuitry determining an attenuation characteristic of the light by each X-ray photon and an output decreased characteristic of the element, based on the values and time when each peak value was detected, correcting the detected values according to the characteristics, a counter counting the X-ray photons corresponding to the respective corrected peak values, wherein the processing circuitry reconstructs a medical image based on an output from the counter.
1. An X-ray computed tomography apparatus comprising:
an X-ray tube configured to generate an X-ray;
an X-ray detector including a scintillator configured to generate scintillation light upon incidence of a plurality of X-ray photons that have been generated from the X-ray tube and have passed through an object, and a photodetection element provided on a rear surface of the scintillator;
a peak value detector configured to detect a plurality of peak values corresponding to respective X-ray photons entering the scintillator based on an output signal from the photodetection element;
processing circuitry configured to determine an attenuation characteristic of the scintillation light by each of the plurality of X-ray photons and an output decreased characteristic of the photodetection element, based on the peak values and time when each of the plurality of peak values was detected, and to correct the plurality of detected peak values in accordance with the attenuation characteristic and the output decreased characteristic; and
a counter configured to count the numbers of X-ray photons corresponding to the respective corrected peak values;
wherein the processing circuitry is configured to reconstruct a medical image based on an output from the counter.
2. The X-ray computed tomography apparatus according to claim 1 , wherein the processing circuitry is configured to determine the attenuation characteristic and the output decreased characteristic, based on the peak values and a time interval between the time and time when the peak value was detected immediately before the time when each of the peak values was detected.
3. The X-ray computed tomography apparatus according to claim 1 , wherein the output decreased characteristic is a characteristic representing a degree of a decrease of a ratio of each of the plurality of peak values to a maximum value that can be output from the photodetection element.
4. The X-ray computed tomography apparatus according to claim 1 , wherein the output decreased characteristic is a characteristic representing a degree of a decrease of the output signal by recharging of the photodetection element.
5. The X-ray computed tomography apparatus according to claim 1 , wherein the processing circuitry is configured to store the output decreased characteristic in accordance with a type of a photoelectric conversion element in the photodetection element.
6. A photon counting method comprising:
detecting a plurality of peak values corresponding to respective X-ray photons entering a scintillator;
determining an attenuation characteristic of scintillation light by each of the plurality of X-ray photons and an output decreased characteristic of a photodetection element based on the peak values and time when each of the plurality of peak values corresponding to the respective X-ray photons was detected, and;
correcting the plurality of detected peak values in accordance with the attenuation characteristic and the output decreased characteristic; and
counting the numbers of X-ray photons corresponding to the respective corrected peak values.
7. The photon counting method according to claim 6 , wherein the determining the attenuation characteristic and the output decreased characteristic is determining the attenuation characteristic and the output decreased characteristic based on the peak values and a time interval between the time and time when the peak value was detected immediately before the time.
8. The photon counting method according to claim 6 , wherein the output decreased characteristic is a characteristic representing a degree of a decrease of a ratio of each of the plurality of peak values to a maximum value that can be output from the photodetection element.
9. The photon counting method according to claim 6 , wherein the output decreased characteristic is a characteristic representing a degree of a decrease of the output signal from the photodetection element by recharging of the photodetection element.
10. The photon counting method according to claim 6 , further comprising storing the output decreased characteristic in accordance with a type of a photoelectric conversion element in the photodetection element.