Radiation imaging apparatus, radiation imaging method, and non-transitory computer-readable storage medium

1. A radiation imaging apparatus, comprising:

a generating unit configured to generate a material characteristic image using a plurality of radiation images of different radiation energy levels captured by a radiation detection apparatus;

a calculation unit configured to calculate evaluation information indicating a correlation between a plurality of material characteristic images; and

an estimation unit configured to estimate an amount of scattered rays included in the plurality of radiation images based on the evaluation information.

2. The radiation imaging apparatus according to claim 1 , wherein the estimation unit generates image information obtained by subtracting a set amount of scattered rays from the radiation image, and the calculation unit calculates the evaluation information based on the image information.

3. The radiation imaging apparatus according to claim 2 , wherein the estimation unit generates image information obtained by changing the setting of the amount of scattered rays, and

the calculation unit repetitively calculates the evaluation information based on the image information generated by the amount of scattered rays with the changed setting.

4. The radiation imaging apparatus according to claim 1 , wherein the calculation unit is configured to determine whether the evaluation information obtained by repetitive calculation has converged, and

when the evaluation information has converged, the estimation unit estimates an amount of scattered rays used to calculate the converged evaluation information as the amount of scattered rays included in the plurality of radiation images.

5. The radiation imaging apparatus according to claim 1 , wherein the generating unit is configured to generate an image of an effective atomic number of a material that forms an object or material separation images separated according to respective materials forming the object as the material characteristic image.

6. The radiation imaging apparatus according to claim 5 , wherein the generating unit is configured to generate a material separation image in which a thickness of the material is corrected based on the estimated amount of scattered rays.

7. The radiation imaging apparatus according to claim 1 , wherein the estimation unit is configured to use a function having pixel value dependence representing a distribution shape of the amount of scattered rays, and

to generate image information by subtracting the amount of scattered rays represented by the function from the radiation image.

8. The radiation imaging apparatus according to claim 1 , wherein the estimation unit is configured to use a function having positional dependence representing a distribution shape of the amount of scattered rays, and

to generate image information by subtracting the amount of scattered rays represented by the function from the radiation image.

9. The radiation imaging apparatus according to claim 1 , wherein the estimation unit is configured to use a function having object imaging part dependence representing a distribution shape of the amount of scattered rays, and

to generate image information by subtracting the amount of scattered rays represented by the function from the radiation image.

10. The radiation imaging apparatus according to claim 7 , wherein the calculation unit is configured to calculate the evaluation information based on the image information, and

to repetitively calculate the evaluation information based on image information generated by an amount of scattered rays in which a value of the function has changed.

11. The radiation imaging apparatus according to claim 1 , wherein the calculation unit is configured to calculate a correlation coefficient indicating a correlation between the plurality of material characteristic images as the evaluation information.

12. The radiation imaging apparatus according to claim 11 , wherein the estimation unit is configured to estimate an amount of scattered rays at which an absolute value of correlation coefficient becomes minimum as the amount of scattered rays included in the plurality of radiation images when the calculation unit calculates the correlation coefficient as the evaluation information.

13. The radiation imaging apparatus according to claim 1 , wherein the calculation unit is configured to calculate mutual information, information entropy, sum of absolute differences or sum of squared differences as the evaluation information that indicates a correlation between the plurality of material characteristic images.

14. The radiation imaging apparatus according to claim 13 , wherein the estimation unit is configured to estimate an amount of scattered rays at which a result of the calculation becomes maximum as the amount of scattered rays included in the plurality of radiation images.

15. The radiation imaging apparatus according to claim 1 , further comprising an obtainment unit configured to obtain a plurality of radiation images captured by the radiation detection apparatus based on a single radiation irradiation operation performed from a radiation generating unit.

16. The radiation imaging apparatus according to claim 15 , wherein the obtainment unit is configured to obtain a plurality of radiation images captured by the radiation detection apparatus as the plurality of radiation images based on different radiation energy levels, and

the generating unit is configured to generate the plurality of material characteristic images based on the plurality of radiation images obtained by the obtainment unit.

17. The radiation imaging apparatus according to claim 1 , further comprising:

a display control unit configured to cause a display unit to display a captured radiation image; and

the display control unit is further configured to display a combined radiation image including an amount of scattered rays, a radiation image obtained by subtracting the amount of scattered rays from the radiation image, or material separation images based on thicknesses of respective separated materials.

18. The radiation imaging apparatus according to claim 17 , wherein the display control unit is configured to cause the display unit to display at least one image displayed on the display unit.

19. A radiation imaging method, comprising the steps of:

generating, by an image processing unit, a material characteristic image using a plurality of radiation images using a plurality of radiation images of different radiation energy levels captured by a radiation detection apparatus;

calculating, by the image processing unit, evaluation information that correlates between a plurality of material characteristic images; and

estimating, by the image processing unit, an amount of scattered rays included in the plurality of radiation images based on the evaluation information.

20. A non-transitory computer-readable storage medium storing a program for causing a computer to execute each step of the radiation imaging method defined in claim 19 .