Image processing apparatus and control method thereof, radiography apparatus, and computer-readable storage medium
An image processing apparatus generates a material characteristic image based on a plurality of radiation images corresponding to a plurality of radiation energies, and estimates at least one of the plurality of radiation energies at a second timing using a plurality of material characteristic images including a material characteristic image generated based on a plurality of radiation images acquired at a first timing and a material characteristic image generated based on a plurality of radiation images acquired at the second timing later than the first timing.
1. An image processing apparatus comprising:
a generation unit configured to generate a material characteristic image based on a plurality of radiation images corresponding to a plurality of radiation energies; and
an estimation unit configured to estimate at least one of the plurality of radiation energies at a second timing using a plurality of material characteristic images including a material characteristic image that the generation unit generated based on a plurality of radiation images acquired at a first timing and a material characteristic image that the generation unit generated based on a plurality of radiation images acquired at the second timing later than the first timing.
2. The image processing apparatus according to claim 1 , wherein the estimation unit estimates at least one of the plurality of radiation energies at the second timing using a similarity of the plurality of material characteristic images.
3. The image processing apparatus according to claim 2 , wherein the similarity uses, as an index, a sum of squared differences, a sum of absolute differences, or a cross-correlation between the material characteristic image generated at the first timing and the material characteristic image generated at the second timing.
4. The image processing apparatus according to claim 1 , wherein the generation unit generates a material characteristic image using a radiation energy of an effective tube voltage acquired based on imaging conditions at the second timing from a table in which effective tube voltages corresponding to imaging conditions including tube voltage and pulse width are registered.
5. The image processing apparatus according to claim 4 , wherein the estimation unit searches for a radiation energy using the effective tube voltage that the generation unit acquired as an initial value such that the similarity between the plurality of material characteristic images becomes larger.
6. The image processing apparatus according to claim 1 , wherein the material characteristic image is an image of a thickness of at least a soft material, a bone, or a contrast agent.
7. The image processing apparatus according to claim 2 , wherein the estimation unit searches for a radiation energy maximizes the similarity by an optimization method.
8. The image processing apparatus according to claim 7 , wherein a convergence condition for the search by the optimization method is any of that the similarity has exceeded a threshold value, that a change in the similarity has entered a predetermined range, and that a loop has been executed a preset number of times met.
9. The image processing apparatus according to claim 1 , wherein the estimation unit starts estimating a radiation energy at the second timing in accordance with a change in an imaging condition including at least one of a tube voltage, a tube current, and a pulse width, and the first timing is a timing that is before an occurrence of the change of the imaging condition.
10. The image processing apparatus according to claim 1 , wherein the estimation unit starts estimating a radiation energy at the second timing in accordance with a detection of degradation of a material characteristic image generated by the generation unit, and the first timing is a timing that is before the detection of the degradation.
11. The image processing apparatus according to claim 1 , wherein the estimation unit performs an estimation of radiation energy at the second timing for each frame of a radiation image.
12. The image processing apparatus according to claim 1 , further comprising a setting unit configured to set in the plurality of material characteristic images a region for calculating a similarity between the plurality of material characteristic images.
13. The image processing apparatus according to claim 12 , wherein the setting unit sets as a region for calculating the similarity a region from which a pixel whose fluctuation of a pixel value between frames of a radiation image is larger than a threshold value has been excluded.
14. The image processing apparatus according to claim 12 , wherein the setting unit sets a region for calculating the similarity in accordance with a specification of a region by a user.
15. The image processing apparatus according to claim 1 , wherein the generation unit acquires a thickness of a specific material by solving a non-linear simultaneous equation obtained based on a radiation attenuation of a specific material corresponding to at least two types of radiation energy and a radiation image corresponding to at least two types of radiation energy.
16. The image processing apparatus according to claim 15 , wherein the generation unit respectively approximates the at least two types of radiation energy to a monochromatic energy and solves the non-linear simultaneous equation.
17. The image processing apparatus according to claim 1 , wherein the estimation unit estimates at least one of the plurality of radiation energies at the second timing by searching for a radiation energy such that a similarity of the plurality of material characteristic images becomes larger.
18. A radiography apparatus comprising:
a radiation detection unit configured to capture a plurality of radiation images corresponding to a plurality of radiation energies;
a generation unit configured to generate a material characteristic image based on the plurality of radiation images captured by the radiation detection unit; and
an estimation unit configured to estimate at least one of the plurality of radiation energies at a second timing using a plurality of material characteristic images including a material characteristic image that the generation unit generated based on the plurality of radiation images that the radiation detection unit acquired at a first timing and a material characteristic image that the generation unit generated based on the plurality of radiation images that the radiation detection unit acquired at the second timing later than the first timing.
19. A method of controlling an image processing apparatus, the method comprising:
generating a material characteristic image based on a plurality of radiation images corresponding to a plurality of radiation energies; and
estimating at least one of the plurality of radiation energies at a second timing using a plurality of material characteristic images including a material characteristic image generated in the generating based on a plurality of radiation images acquired at a first timing and a material characteristic image generated in the generating based on a plurality of radiation images acquired at the second timing later than the first timing.
20. A non-transitory computer-readable storage medium storing a program for causing a computer to execute the method according to claim 19 .