Gamma camera, spect device, pet device, and method for generating measured gamma ray images

A gamma camera, comprising:

• a pixel-type gamma-ray detector;
• and
• an information processing device including,
• a storage device which stores in advance, as detector-response data, energy spectra which are obtained when gamma-rays emitted from one or more objects to be measured are incident without being scattered, and
• an image display device;
• wherein
• the information processing device includes,
• a first processor which generates a main-measurement count image and a subsidiary-measurement count image on the basis of integrated counts which are respectively measured by a main measurement energy window and a subsidiary measurement energy window, where the main measurement energy window is set for gamma-rays emitted from an object to be measured, and the subsidiary measurement energy window is different from the main measurement energy window,
• a second processor which calculates, as a detector response ratio, a ratio of an integrated count included in the main measurement energy window to an integrated count included in the subsidiary measurement energy window, in the detector-response data stored in the storage device,
• a third processor which estimates an integrated count of scattered gamma-rays included in the subsidiary-measurement count image,
• a fourth processor which estimates an integrated count of primary gamma-rays included in the main-measurement count image,
• a fifth processor which determines whether or not the integrated count of primary gamma-rays estimated by the fourth processor converges, and makes the operations of the third processor and the fourth processor repeatedly performed until the integrated count of primary gamma-rays estimated by the fourth processor is determined to converge, and
• a sixth processor which generates a gamma-ray measurement image based on the integrated count of primary gamma-rays estimated by the fifth processor, and displays the gamma-ray measurement image on the image display device, when convergence is determined by the fifth processor;
• wherein in an initial cycle in the repeatedly performed operations, the third processor estimates, as an integrated count of scattered gamma-rays included in the subsidiary-measurement count image, a value obtained by subtracting a product of the detector response ratio and the main-measurement count image, from the subsidiary-measurement count image obtained by the first processing,
• in following cycles in the repeatedly performed operations, the third processor estimates, as the integrated count of scattered gamma-rays included in the subsidiary-measurement count image, a value obtained by subtracting a product of the detector response ratio and the integrated count of primary gamma-rays included in the main-measurement count image from the subsidiary-measurement count image obtained by the first processor, which is estimated by the fourth processor, and
• the fourth processor estimates an integrated count of scattered gamma-rays included in the main-measurement count image on the basis of the integrated count of scattered gamma-rays included in the subsidiary-measurement count image which is estimated by the third processor, and estimates an integrated count of primary gamma-rays included in the main-measurement count image by subtracting the estimated integrated count of scattered gamma-rays included in the main-measurement count image from the subsidiary-measurement count image obtained by the first processor.

A method for generating a gamma-ray measurement image, executed in a gamma camera which includes,

• a pixel-type gamma-ray detector;
• and
• an information processing device including,
• a storage device which stores in advance, as detector-response data, energy spectra which are obtained when gamma-rays emitted from one or more objects to be measured are incident without being scattered, and
• an image display device;
• wherein
• the information processing device performs:
• a first step of generating a main-measurement count image and a subsidiary-measurement count image on the basis of integrated counts which are respectively measured by a main measurement energy window and a subsidiary measurement energy window, where the main measurement energy window is set for gamma-rays emitted from an object to be measured, and the subsidiary measurement energy window is different from the main measurement energy window;
• a second step of estimating an integrated count of scattered gamma-rays included in the subsidiary-measurement count image, by estimating an integrated count of primary gamma-rays included in the subsidiary measurement energy window on the basis of the detector-response data and the main-measurement count image, and subtracting the estimated integrated count of primary gamma-rays included in the subsidiary measurement energy window from the subsidiary-measurement count image;
• a third step of estimating an integrated count of primary gamma-rays included in the main measurement energy window, on the basis of the integrated count of scattered gamma-rays included in the subsidiary measurement energy window, which is estimated in the second step;
• and
• a fourth step of generating a gamma-ray measurement image on the basis of the integrated count of primary gamma-rays estimated by the third step, and displaying the gamma-ray measurement image on the image display device.

A method for generating a gamma-ray measurement image, executed in a gamma camera which includes,

• a pixel-type gamma-ray detector;
• and
• an information processing device including,
• a storage device which stores in advance, as detector-response data, energy spectra which are obtained when gamma-rays emitted from one or more objects to be measured are incident without being scattered, and
• an image display device;
• wherein
• the information processing device performs:
• a first step of generating a main-measurement count image and a subsidiary-measurement count image on the basis of integrated counts which are respectively measured by a main measurement energy window and a subsidiary measurement energy window, where the main measurement energy window is set for gamma-rays emitted from an object to be measured, and the subsidiary measurement energy window is different from the main measurement energy window;
• a second step of calculating, as a detector response ratio, a ratio of an integrated count included in the main measurement energy window to an integrated count included in the subsidiary measurement energy window, in the detector-response data stored in the storage device;
• a third step of estimating an integrated count of scattered gamma-rays included in the subsidiary-measurement count image;
• a fourth step of estimating an integrated count of primary gamma-rays included in the main-measurement count image;
• a fifth step of determining whether or not the integrated count of primary gamma-rays estimated in the fourth step converges, and making operations in the third step and the fourth step repeatedly performed until the integrated count of primary gamma-rays estimated in the fourth step is determined to converge;
• and
• a sixth step of generating a gamma-ray measurement image based on the integrated count of primary gamma-rays estimated in the fifth step, and displaying the gamma-ray measurement image on the image display device, when convergence is determined in the fifth step;
• wherein in the third step in an initial cycle in the repeatedly performed operations, a value obtained by subtracting a product of the detector response ratio and the main-measurement count image from the subsidiary-measurement count image obtained in the first step is estimated as an integrated count of scattered gamma-rays included in the subsidiary-measurement count image,
• in the third step in following cycles in the repeatedly performed operations, a value obtained by subtracting a product of the detector response ratio and the integrated count of primary gamma-rays included in the main-measurement count image, which is estimated in the fourth step, from the subsidiary-measurement count image obtained in the first step is estimated as the integrated count of scattered gamma-rays included in the subsidiary-measurement count image, and
• in the fourth step, an integrated count of scattered gamma-rays included in the main-measurement count image is estimated on the basis of the integrated count of scattered gamma-rays included in the subsidiary-measurement count image which is estimated in the third step, and an integrated count of primary gamma-rays included in the main-measurement count image is estimated by subtracting the estimated integrated count of scattered gamma-rays included in the main-measurement count image from the subsidiary-measurement count image obtained in the first step.