Image processing apparatus, image processing method, and non-transitory computer-readable storage medium
An image processing apparatus comprises a processing unit configured to performing energy subtraction processing using information concerning a plurality of attenuation rates corresponding to a plurality of radiation energies that are different from each other and are obtained by performing imaging in which an object is irradiated with radiation. The processing unit estimates attenuation information of a decomposition target material contained in the object using at least one image obtained by the energy subtraction processing, and generates an image concerning the decomposition target material using the attenuation information and the information concerning the plurality of attenuation rates.
1 . An image processing apparatus that generates an image of a first material and an image of a second material contained in an object, comprising:
a processing unit configured to performing energy subtraction processing using information concerning a plurality of attenuation rates corresponding to a plurality of radiation energies that are different from each other and are obtained by performing imaging in which the object is irradiated with radiation,
wherein the processing unit
estimates a linear attenuation coefficient of the first material at an energy of the radiation, (a) using at least one of information concerning an effective atomic number and information concerning a surface density that are obtained by the energy subtraction processing, or (b) using at least one of information concerning a thickness of a third material and information concerning a thickness of a fourth material that are contained in the first material obtained by the energy subtraction processing, and (c) using a linear attenuation coefficient of the third material, a density of the third material, a linear attenuation of the fourth material, and a density of the fourth material, and
generates an image of the first material and an image of the second material using the linear attenuation coefficient and the information concerning the plurality of attenuation rates.
2 . The image processing apparatus according to claim 1 ,
wherein the processing unit
estimates the attenuation information of the first material, (a) using pixel values in an image of the effective atomic number, or (b) using ratio information of the third material contained in the first material, which is obtained using an image of the thickness of the third material and an image of the thickness of the fourth material, and
generates the image of the first material and the image of the second material by performing the energy subtraction processing using the attenuation information and the information concerning the plurality of attenuation rates.
3 . The image processing apparatus according to claim 1 , wherein the third material is water contained in a soft tissue of the object, and the fourth material is fat contained in the soft tissue.
4 . The image processing apparatus according to claim 1 , wherein the first material is a soft tissue contained in the object, and the second material is a bone contained in the object.
5 . The image processing apparatus according to claim 1 , wherein
the processing unit
estimates, as the attenuation information, a linear attenuation coefficient of the first material at an energy of the radiation, and
generates images decomposed into a thickness of the first material and a thickness of the second material by the energy subtraction processing using the plurality of attenuation rates and the attenuation information.
6 . The image processing apparatus according to claim 1 , wherein the processing unit uses actually measured values as the linear attenuation coefficient of the third material and the linear attenuation coefficient of the fourth material, or the density of the third material and the density of the fourth material.
7 . The image processing apparatus according to claim 1 , wherein
the processing unit
estimates, as the attenuation information, a mass attenuation coefficient of the first material at an energy of the radiation, and
generates an image of a surface density of the first material and an image of a surface density of the second material by the energy subtraction processing using the plurality of attenuation rates and the attenuation information.
8 . The image processing apparatus according to claim 1 , wherein
the processing unit includes
a first table in which a thickness of the second material and the thickness of the third material are registered in accordance with a combination of the plurality of attenuation rates, and
a second table in which the thickness of the second material and the thickness of the fourth material are registered in accordance with the combination of the plurality of attenuation rates.
9 . The image processing apparatus according to claim 8 , wherein
the processing unit
obtains a thickness image of the second material based on the thickness of the second material obtained using the first table, the thickness of the second material obtained using the second table, and ratio information of the third material contained in the first material, and
obtains a thickness image of the first material based on the thickness of the third material obtained using the first table, the thickness of the fourth material obtained using the second table, and the ratio information.
10 . The image processing apparatus according to claim 1 , wherein
the processing unit
estimates the attenuation information of the first material by averaging pixel values in an image of the effective atomic number, and
divides the image of the effective atomic number into a plurality of regions, and averages the pixel values of the image of the effective atomic number for each divided region, thereby estimating the attenuation information of the first material in each region.
11 . The image processing apparatus according to claim 1 , wherein
the processing unit
estimates the attenuation information of the first material by averaging pixel values in an image of the effective atomic number, and
determines a pixel whose effective atomic number exceeds a threshold as a pixel in a region where the second material exists in the image of the effective atomic number, and performs processing such that a pixel value determined as a pixel in the region is not included in the averaging calculation.
12 . The image processing apparatus according to claim 1 , wherein
the processing unit
estimates the attenuation information of the first material by averaging pixel values in an image of the effective atomic number, and
determines a pixel whose surface density obtained by averaging pixel values obtained by the energy subtraction processing falls below a surface density threshold as a pixel in a region where the object does not exist, and performs processing such that a pixel value determined as a pixel in the region is not included in the averaging calculation.
13 . The image processing apparatus according to claim 1 , wherein
the processing unit estimates the attenuation information of the first material from ratio information of the third material contained in the first material, which is obtained by averaging pixel values of a plurality of pixels in the thickness of the third material and the thickness of the fourth material.
14 . The image processing apparatus according to claim 13 , wherein the processing unit divides the thickness of the third material and the thickness of the fourth material into a plurality of regions and averages the ratio information for each region, thereby estimating the attenuation information of the first material in each region.
15 . The image processing apparatus according to claim 13 , wherein
the processing unit determines a pixel whose ratio information exceeds a ratio threshold as a pixel in a region where the second material exists in the thickness of the third material and the thickness of the fourth material, and performs processing such that a pixel value determined as a pixel in the region is not included in the averaging calculation.
16 . The image processing apparatus according to claim 13 , wherein
the processing unit determines a pixel for which a total thickness of the third material and the fourth material falls below a thickness threshold as a pixel in a region where the object does not exist, and performs processing such that a pixel value determined as a pixel in the region is not included in the averaging calculation.
17 . An image processing method of an image processing apparatus that generates an image of a first material and an image of a second material contained in an object, the image processing method comprising
a processing step of performing energy subtraction processing using information concerning a plurality of attenuation rates corresponding to a plurality of radiation energies that are different from each other and are obtained by performing imaging in which an object is irradiated with radiation,
wherein in the processing step,
a linear attenuation coefficient of the first material at an energy of the radiation is estimated, (a) using at least one of information concerning an effective atomic number and information concerning a surface density that are obtained by the energy subtraction processing, or (b) using at least one of information concerning a thickness of a third material and information concerning a thickness of a fourth material that are contained in the first material obtained by the energy subtraction processing, and (c) using a linear attenuation coefficient of the third material, a density of the third material, a linear attenuation coefficient of the fourth material, and a density of the fourth material, and
an image of the first material and an image of the second material is generated using the linear attenuation coefficient and the information concerning the plurality of attenuation rates.
18 . A non-transitory computer-readable storage medium storing a program for causing a computer to execute the method according to claim 17 .