X-ray CT apparatus including a photon-counting detector, and an image processing apparatus and an image processing method for correcting detection signals detected by the photon-counting detector

1. An X-ray computed tomography (CT) apparatus comprising:

a photon-counting detector configured to include a plurality of X-ray detection elements detecting X-ray photons applied from an X-ray tube;

correction circuitry configured to correct detection signals detected by the photon-counting detector for the plurality of X-ray detection elements, based on a centroid of an X-ray spectrum detected by the photon-counting detector; and

reconstruction circuitry configured to reconstruct a CT image based on the corrected detection signals.

2. The X-ray CT apparatus according to claim 1 , further comprising:

a calculator configured to calculate correction values, for the plurality of X-ray detection elements, to match a reference centroid serving as a centroid of a reference X-ray spectrum with the centroid of the X-ray spectrum detected by the photon-counting detector, wherein

the correction circuitry corrects the detection signals detected by the photon-counting detector for the (plurality of X-ray detection elements, based on the correction values calculated for the plurality of X-ray detection elements.

3. The X-ray CT apparatus according to claim 2 , wherein the calculator calculates the reference X-ray spectrum from a detection signal detected using a spectrometer, and determines the reference centroid from the reference X-ray spectrum, to calculate the correction values for the plurality of X-ray detection elements.

4. The X-ray CT apparatus according to claim 3 , wherein

the calculator calculates the correction values for the plurality of X-ray detection elements in accordance with a tube voltage of the X-ray tube, and

the correction circuitry corrects the detection signals detected by the photon-counting detector for the plurality of X-ray detection elements, based on the correction values in accordance with the tube voltage of the X-ray tube.

5. The X-ray CT apparatus according to claim 2 , further comprising:

a reference detection element configured to have higher energy resolution than that of the plurality of X-ray detection elements included in the photon-counting detector, wherein

the calculator determines the reference X-ray spectrum from a detection signal detected using the reference detection element, and determines the reference centroid based on characteristic X-rays of the reference X-ray spectrum, to calculate the correction values for the plurality of X-ray detection elements.

6. The X-ray CT apparatus according to claim 5 , further comprising:

a movement controller configured to control movement of the photon-counting detector in a channel direction independently of the X-ray tube, and perform control to match a position of the reference detection element in the channel direction when the reference centroid is determined with a position of an X-ray detection element of the plurality of X-ray detection elements that is to be corrected in the channel direction.

7. The X-ray CT apparatus according to claim 6 , wherein the movement controller places the reference detection element in a position opposed to the X-ray tube when the reference centroid is determined, and places the X-ray detection element of the plurality of X-ray detection elements that is to be corrected in the position opposed to the X-ray tube.

8. The X-ray CT apparatus according to claim 6 , wherein the movement controller places the reference detection element in a position agreeing with a relative position between the X-ray detection element of the plurality of X-ray detection elements that is to be corrected and the X-ray tube in a state where a center of the photon-counting detector is opposed to the X-ray tube when the reference centroid is determined, and places the center of the photon-counting detector in the position opposed to the X-ray tube.

9. The X-ray CT apparatus according to claim 5 , wherein the photon-counting detector includes the reference detection element in at least part of the plurality of X-ray detection elements.

10. The X-ray CT apparatus according to claim 2 , further comprising:

a spectrum processor configured to preprocess the reference X-ray spectrum, wherein

the calculator calculates the reference centroid from the preprocessed reference X-ray spectrum, to calculate the correction values for the plurality of X-ray detection elements.

11. The X-ray CT apparatus according to claim 1 , wherein the photon-counting detector is an area detector.

12. The X-ray CT apparatus according to claim 1 , wherein the centroid of the X-ray spectrum is an energy position in which an area of X-ray spectrum in an energy band higher than the centroid is equal to an area of X-ray spectrum in an energy band lower than the centroid.

13. An image processing apparatus, comprising:

correction circuitry configured to correct detection signals detected by a photon-counting detector including a plurality of X-ray detection elements configured to detect X-ray photons applied from an X-ray tube, for the plurality of X-ray detection elements, based on a centroid of an X-ray spectrum detected by the photon-counting detector; and

reconstruction circuitry configured to reconstruct a computed tomography (CT) image based on the corrected detection signals.

14. An image processing method comprising:

correcting detection signals detected by a photon-counting detector including a plurality of X-ray detection elements configured to detect X-ray photons applied from an X-ray tube, for the plurality of X-ray detection elements, based on a centroid of an X-ray spectrum detected by the photon-counting detector; and

reconstructing a computed tomography (CT) image based on the corrected detection signals.