Photon counting X-ray CT apparatus

1. A photon counting X-ray CT apparatus comprising:

data acquiring circuitry configured to allocate energy measured by signals output from a photon counting detector in response to absorption of X-ray photons, the energy being allocated to respective first energy bins so as to acquire a first data group as count data of each of the first energy bins; and

processing circuitry configured to:

determine second energy bins obtained by grouping the first energy bins in accordance with a decomposition target material that is a material to be decomposed in a imaging region,

allocate the first data group to respective of the second energy bins so as to generate a second data group, and

use the second data group to generate an image representing a distribution of the decomposition target material, wherein

the processing circuitry determines the second energy bins so that a K absorption edge of the decomposition target material substantially coincides with a boundary between adjacent energy bins of the second energy bins,

the processing circuitry arranges the second energy bins at irregular intervals, and

the processing circuitry selects widths of the second energy bins based on each of integrated values of X-ray absorption rate corresponding to each of the second energy bins.

2. The photon counting X-ray CT apparatus according to claim 1 , wherein the processing circuitry determines whether the decomposition target material is present in the imaging region, and determines the second energy bins obtained by grouping at least two-of the first energy bins when the decomposition target material is determined to be present in the imaging region.

3. The photon counting X-ray CT apparatus according to claim 1 , wherein the processing circuitry is further configured to

generate a CT image by performing a reconstructing process using all or a part of the first data group,

determine whether the decomposition target material is present in the imaging region, based on CT value of the CT image and CT value corresponding to the decomposition target material,

determine the second energy bins when the decomposition target material is present in the imaging region, and

generate the image representing the distribution of the decomposition target material when the decomposition target material is determined to be present.

4. The photon counting X-ray CT apparatus according to claim 1 , wherein the processing circuitry is further configured to

estimate an energy spectrum based on the first data group,

determine whether the decomposition target material is present in the imaging region based on the estimated energy spectrum,

determine the second energy bins when the decomposition target material is determined to be present in the imaging region, and

generate the image representing the distribution of the decomposition target material when the decomposition target material is determined to be present.

5. The photon counting X-ray CT apparatus according to claim 1 , further comprising

input circuitry configured to receive information from a user, wherein

the processing circuitry obtains, based on the information received by the input circuitry, a material as the decomposition target material and a certain energy unique to the material and uses the obtained certain energy to determine the second energy bins.

6. The photon counting X-ray CT apparatus according to claim 1 , wherein the processing circuitry selects the widths of the second energy bins so that each of the integral values of the X-ray absorption rate corresponding to each of the second energy bins is a same value.

7. The photon counting X-ray CT apparatus according to claim 5 , further comprising

a display that displays a list of candidate materials for the decomposition target material, wherein

the input circuitry receives information on the candidate materials for the decomposition target material from the user who has referred to the display.

8. The photon counting X-ray CT apparatus according to claim 5 , wherein the input circuitry includes at least one input receiving component associated with at least one candidate material for the decomposition target material and receives information on the material associated with the input receiving component operated by the user.

9. The photon counting X-ray CT apparatus according to claim 5 , wherein the input circuitry generates identifiers each combining one or more materials to be decomposition target materials in accordance with a request from the user, causes the display to display information on the identifiers, and receives information on the materials as the decomposition target materials from the user who has referred to the display.

10. A photon counting X-ray CT apparatus comprising:

an X-ray tube that generates X-rays;

a detector including a plurality of detecting elements configured to output signals based on the incident X-rays;

processing circuitry configured to

obtain information on decomposition target material to be decomposed among materials possible to be present in a certain region in a subject from which projection data of a plurality of first energy bins set on an energy distribution of the X-rays emitted from the X-ray tube has been acquired,

identify, based on the information on the decomposition target material, first energy bins to be used for the material decomposition among the first energy bins set on the energy distribution of the X-rays,

use the projection data of the identified first energy bins to perform the material decomposition, and

generate an image for displaying a result of the material decomposition; and

data acquiring circuitry configured to allocate the signals to respective of the first energy bins according to energy measured based on the signals so as to acquire a first data group as count data of each of the first energy bins, wherein

the processing circuitry is further configured to

determine a plurality of second energy bins obtained by grouping the identified first energy bins in response to the decomposition target materials on which the information has been acquired so that a K absorption edge of the decomposition target material substantially coincides with a boundary between adjacent energy bins of the second energy bins

allocate the first data group to respective of the second energy bins so as to generate a second data group, and

use the second data group to generate an image representing a distribution of the decomposition target material, and

the processing circuitry is further configured to

arrange the second energy bins at irregular intervals, and

select widths of the second energy bins based on each of integrated values of X-ray absorption rate corresponding to each of the second energy bins.

11. The photon counting X-ray CT apparatus according to claim 10 , wherein the processing circuitry identifies, as a first subset of energy bins to be used for the material decomposition among the first energy bins, a smaller number of energy bins than a total number of the first energy bins, in the descending order of the energy.

12. The photon counting X-ray CT apparatus according to claim 10 , wherein the processing circuitry identifies, as a first subset of energy bins to be used for the material decomposition among the first energy bins, first energy bins that do not overlap a K absorption edge of the decomposition target material.

13. The photon counting X-ray CT apparatus according to claim 10 , wherein the processing circuitry is further configured to

determine whether the decomposition target material is present in a imaging region, and

determine the second energy bins obtained by grouping at least some of the first energy bins when the decomposition target material is determined to be present in the imaging region.