Nuclear medical diagnostic apparatus and image processing method
According to one embodiment, a nuclear medical diagnostic apparatus includes processing circuitry. The processing circuitry acquires gamma-ray emission data based on gamma rays emitted from radio isotopes administered to an object. The processing circuitry further executes scattered-ray correction on the gamma-ray emission data based on a second X-ray CT image obtained by replacing pixel values of a non-object region included in a first X-ray CT image with a predetermined pixel value.
1. A nuclear medical diagnostic apparatus comprising:
processing circuitry configured to:
acquire gamma-ray emission data based on gamma rays emitted from radio isotopes administered to an object;
obtain a first X-ray CT image by imaging the object;
perform image processing on the first X-ray CT image to estimate a position of a non-object region in the first X-ray CT image;
extract the non-object region from the first X-ray CT image based on the estimated position of the non-object region;
obtain a second X-ray CT image by replacing pixel values of the extracted non-object region in the first X-ray CT image with a predetermined pixel value to increase a number of pixels in a tail region that corresponds to a scattering region where any radioactivity is not supposed to exist;
estimate a scattered ray distribution by approximating the tail region in which the number of the pixels are increased; and
execute scattered-ray correction on the gamma-ray emission data based on the second X-ray CT image by a tail fitting method using the scattered ray distribution.
2. The nuclear medical diagnostic apparatus according to claim 1 , wherein the processing circuitry is configured to execute the scattered-ray correction on the gamma-ray emission data based on forward projection data obtained by performing forward projection on the second X-ray CT image.
3. The nuclear medical diagnostic apparatus according to claim 2 , wherein the processing circuitry is configured to generate the forward projection data by performing the forward projection on the second X-ray CT image.
4. The nuclear medical diagnostic apparatus according to claim 1 , wherein the non-object region is an imaging region of a top plate included in the first X-ray CT image and the predetermined pixel value is a pixel value corresponding to a CT value of air.
5. The nuclear medical diagnostic apparatus according to claim 1 , wherein the second X-ray CT image is obtained by further replacing pixel values of the extracted non-object region that still remains in the first X-ray CT image with the predetermined pixel value according to a user's command inputted via an input circuit.
6. The nuclear medical diagnostic apparatus according to claim 1 , wherein, when the processing circuitry generates the second X-ray CT image from the first X-ray CT image for a predetermined slice, the processing circuitry is configured to store information on a pixel position of the extracted non-object region in the first X-ray CT image in a memory circuit.
7. The nuclear medical diagnostic apparatus according to claim 6 , wherein the processing circuitry is configured to generate the second X-ray CT image from the first X-ray CT image for a slice other than the predetermined slice by using the information on the pixel position of the extracted non-object region in the first X-ray CT image stored in the memory circuit.
8. The nuclear medical diagnostic apparatus according to claim 1 , wherein the processing circuitry is configured to execute attenuation correction on the gamma-ray emission data based on a gamma-ray attenuation coefficient map of the object generated by using pixel values of a region of the object included in the first X-ray CT image.
9. The nuclear medical diagnostic apparatus according to claim 8 , wherein the processing circuitry is configured to generate the gamma-ray attenuation coefficient map of the object by using the pixel values of the region of the object included in the first X-ray CT image.
10. The nuclear medical diagnostic apparatus according to claim 1 , wherein the processing circuitry is configured to generate a nuclear medical image based on the gamma-ray emission data subjected to the scattered-ray correction and to display the nuclear medical image on a display.
11. An image processing method comprising:
acquiring gamma-ray emission data based on gamma rays emitted from radio isotopes administered to an object;
obtaining a first X-ray CT image by imaging the object;
performing image processing on the first X-ray CT image to estimate a position of a non-object region in the first X-ray CT image;
extracting the non-object region from the first X-ray CT image based on the estimated position of the non-object region;
obtaining a second X-ray CT image by replacing pixel values of the extracted non-object region included in the first X-ray CT image with a predetermined pixel value to increase a number of pixels in a tail region that corresponds to a scattering region where any radioactivity is not supposed to exist;
estimating a scattered ray distribution by approximating the tail region in which the number of the pixels are increased; and
executing scattered-ray correction on the gamma-ray emission data based on the second X-ray CT image by a tail fitting method using the scattered ray distribution.