Image processing apparatus, radiation imaging system, image processing method, and storage medium
An image processing apparatus includes a processing unit configured to, by using a plurality of pieces of information that correspond to a plurality of mutually different radiation energies and that have been obtained by irradiating an object with radiation and performing imaging, and information regarding transmittance including scattered rays and transmittance not including the scattered rays that is set in advance for each of multiple thicknesses of a first material and a second material that is different from the first material, obtain thickness images of the first and second materials in which the scattered rays have been corrected.
1 . An image processing apparatus, comprising:
a processing unit configured to obtain thickness images of first and second materials in which scattered rays have been corrected using a plurality of pieces of information that correspond to a plurality of mutually different radiation energies and that have been obtained by irradiating an object with radiation and performing imaging, and information regarding transmittance including scattered rays and transmittance not including the scattered rays that is set in advance for each of multiple thicknesses of a first material and a second material that is different from the first material; and
a storage unit configured to store information regarding the transmittance obtained for each of multiple thicknesses of a predetermined material for each of a first radiation energy and a second radiation energy that is different from the first radiation energy;
the processing unit being configured to obtain information regarding transmittance that corresponds to a thickness of the predetermined material by performing correction of the information stored in the storage unit, the information regarding transmittance including the scattered rays obtained for each combination of a thickness of the first material and a thickness of the second material is stored in the storage unit; and
the processing unit being configured to obtain information regarding transmittance including the scattered rays for the combination by performing correction of the information obtained from the storage unit based on the combination, wherein
when the scattered rays are not included in the first radiation energy, the processing unit is configured to generate a first function that outputs information regarding transmittance from a combination of a thickness of the first material and a thickness of the second material including the scattered rays for the combination,
when the scattered rays are not included in the second radiation energy, the processing unit is configured to generate a second function that outputs information regarding transmittance from a combination of a thickness of the first material and a thickness of the second material including the scattered rays for the combination, and
the processing unit is configured to obtain a first change rate of the first function and a second change rate of the second function based on a change in thickness of the first material, and to obtain a third change rate of the first function and a fourth change rate of the second function based on a change in thickness of the second material.
2 . The image processing apparatus according to claim 1 , wherein information that corresponds to a first radiation energy includes a first radiation image among the plurality of radiation energies, and information that corresponds to a second radiation energy includes a second radiation image, among the plurality of radiation energies that is different from the first radiation energy.
3 . The image processing apparatus according to claim 2 , wherein the first radiation image includes data in which signal values of electric signals obtained by the imaging and position information indicating a two-dimensional array of the signal values are associated with one another, and
the second radiation image includes data in which signal values of electric signals obtained by the imaging and position information indicating a two-dimensional array of the signal values are associated with one another.
4 . The image processing apparatus according to claim 1 , wherein the processing unit is configured to obtain information regarding transmittance including the scattered rays at the first radiation energy and information regarding transmittance including the scattered rays at the second radiation energy as a result of the correction.
5 . The image processing apparatus according to claim 1 , wherein the processing unit is configured to obtain a first difference between transmittance not including the scattered rays at the first radiation energy and transmittance including the scattered rays output from the first function, and
is configured to obtain a second difference between transmittance not including the scattered rays at the second radiation energy and transmittance including the scattered rays output from the second function.
6 . The image processing apparatus according to claim 5 , wherein the processing unit is configured to obtain the thickness image of the first material by repeatedly executing energy subtraction processing in which the fourth change rate and the first difference, and the third change rate and the second difference are used, and
is configured to obtain the thickness image of the second material by repeatedly executing energy subtraction processing in which the second change rate and the first difference, and the first change rate and the second difference are used.
7 . The image processing apparatus according to claim 6 , wherein the processing unit is configured to obtain an image of first transmittance not including the scattered rays in which a scattered-ray component has been reduced from the transmittance including the scattered rays output from the first function, and
is configured to obtain an image of second transmittance not including the scattered rays in which a scattered-ray component has been reduced from the transmittance including scattered rays output from the second function, and
is configured to obtain the thickness image of the first material and the thickness image of the second material in which the scattered-ray component has been reduced using the image of the first transmittance and the image of the second transmittance.
8 . The image processing apparatus according to claim 1 , wherein the processing unit is configured to obtain transmittance not including the scattered rays that corresponds to the thickness of the predetermined material by performing correction in which transmittance including the scattered rays and transmittance not including the scattered rays stored in the storage unit are used.
9 . The image processing apparatus according to claim 8 , wherein the storage unit is configured to store a ratio between a scattered-ray component included in the radiation and a primary-radiation component corresponding to the radiation directly reaching a two-dimensional detector from a radiation source for each of multiple thicknesses of the predetermined material, and
the processing unit is configured to obtain the transmittance not including the scattered rays that corresponds to the thickness of the predetermined material by performing correction in which the ratio and transmittance including the scattered rays are used.
10 . The image processing apparatus according to claim 8 , wherein the storage unit is configured to store a difference between transmittance including the scattered rays and transmittance not including the scattered rays for each of multiple thicknesses of the predetermined material, and
the processing unit is configured to obtain the transmittance not including the scattered rays that corresponds to the thickness of the predetermined material by performing correction in which the difference and transmittance including the scattered rays are used.
11 . The image processing apparatus according to claim 1 , wherein the storage unit is configured to store information regarding the transmittance obtained for each of multiple distances between the object and a two-dimensional detector for detecting the radiation, and
the processing unit is configured to obtain the information regarding transmittance that corresponds to the thickness of the predetermined material using the information obtained by performing interpolation based on the distance of the object during imaging.
12 . The image processing apparatus according to claim 1 , wherein the thickness image of the first material is a bone image, and the thickness image of the second material is a soft tissue image.
13 . A radiation imaging system, comprising:
a radiation imaging apparatus including a two-dimensional detector; and
the image processing apparatus according to claim 1 , the image processing apparatus being configured to obtain images in which scattered rays included in radiation detected by the two-dimensional detector have been corrected.
14 . An image processing method, comprising:
obtaining thickness images of first and second materials in which scattered rays have been corrected using a plurality of pieces of information that correspond to a plurality of mutually different radiation energies and that have been obtained by irradiating an object with radiation and performing imaging, and information regarding transmittance including scattered rays and transmittance not including the scattered rays that is set in advance for each of multiple thicknesses of a first material and a second material that is different from the first material;
storing information regarding the transmittance obtained for each of multiple thicknesses of a predetermined material for each of a first radiation energy and a second radiation energy that is different from the first radiation energy; and
obtaining information regarding transmittance that corresponds to a thickness of the predetermined material by performing correction of the stored information, the information regarding transmittance including the scattered rays obtained for each combination of a thickness of the first material and a thickness of the second material, wherein
obtaining information regarding transmittance by performing correction of the information obtained from the storage unit based on the combination, including the scattered rays for the combination,
when the scattered rays are not included in the first radiation energy, generating a first function that outputs information regarding transmittance including the scattered rays for the combination, from a combination of a thickness of the first material and a thickness of the second material,
when the scattered rays are not included in the second radiation energy, generating a second function that outputs information regarding transmittance including the scattered rays for the combination, from a combination of a thickness of the first material and a thickness of the second material, and
obtaining a first change rate of the first function and a second change rate of the second function based on a change in thickness of the first material, and obtaining a third change rate of the first function and a fourth change rate of the second function based on a change in thickness of the second material.
15 . A non-transitory storage medium in which is stored a program that causes a computer to execute the image processing method according to claim 14 .