Digital Position and Depth of Interaction Measurement of the PET Detector Through the Signal Ratio

Abstract

A new detector was designed to improve the spatial resolution of positron emission tomography (PET) and acquire digital coordinates of the detector"s scintillation pixels. In order to solve the spatial resolution deterioration phenomenon due to parallax error occurring outside the field of view (FOV), a method of measuring the depth of interaction was developed, and this was accomplished with the acquisition of digital coordinates. A detector using a 4 × 4 × 2 GAGG scintillator was designed using the DETECT2000 simulation tool to acquire digital coordinates of the scintillation pixels and measure the depth of interaction of the two layers. A gamma-ray reaction was generated in all the scintillation pixels, and the signals were obtained from SiPM pixels in a 4 × 4 array. The 16-channels of optical sensor signals were reduced to signals of 4 channels, and these were calculated as a ratio of each signal. The ratio of the signal was obtained from all the flash pixels, and the position was obtained as digital coordinates by comparing it with the ratio of the signal by the gamma ray response generated at the new position. In order to evaluate the accuracy of acquiring the digital coordinates and the accuracy of the layer where the scintillation pixel in which the scintillator and the gamma ray reacted, a signal was obtained by generating a gamma ray response for the entire length of each scintillation pixel. Gamma-ray reactions were generated at intervals of 0.2 mm from 0.1 mm to 19.9 mm. The obtained signals through these reactions were compared with the signals of each scintillation pixel obtained in advance. Then, the accuracy of measured positions on the X, Y, and Z axes were evaluated. The accuracy of both the X and Y axis showed perfect results, and the accuracy of the Z axis was 91.46 %.