A point source method to position 2D position-sensitive detectors correctly to obtain brain PET images with a resolution of 1 mm over a region of 25 cm

Positron emission tomography (PET) is used to research high order functions in the brain. There is a lot of brain activity in the gray matter. To study the function of the corpus callosum in gray matter, a spatial resolution of approximately 1 mm is necessary. Using 640 two-dimensional position-sensitive cadmium tellurium (CdTe) detectors with a spatial full width half maximum (FWHM) resolution of 1 mm, we made a brain PET. Our aim was to obtain a resolution (FWHM) of 1 mm at a position 100 mm from the center of the gantry. Though the positions of the 640 detectors can be estimated based on the shape of the gantry, it is not easy to determine their exact positions. We developed a method to determine the detector position by analyzing the distribution of the lines-of-response (LORs) between two detector blocks. We obtained this distribution by measuring a sodium (²²Na) point source with a diameter of 1 mm. We reconstructed images of the point source using the maximum likelihood-expectation maximization (ML-EM) method using the corrected positions of the detectors. We succeeded in achieving a resolution (FWHM) of 1.6 mm at a distance of 100 mm from the center of the gantry.