Effect of temperature on the performance of brain PET using GAPD

A PET employing Geiger-mode avalanche photodiode (GAPD) has been designed and developed in our laboratory for simultaneous human brain PET-MR imaging. The purpose of this study is to evaluate the effect of temperature on the performance of the brain PET. The PET gantry including LYSO and GAPD array were placed in a temperature controlled chamber. All electronics including preamplifiers were located outside the chamber to minimize the temperature effect. Energy resolution and photo-peak position of all channels of the brain PET were measured. Count rates of the PET were also measured using 2 different Schemes: fixed energy window and adjusted energy window. All measurement was performed at 10°C ~ 40°C with 5°C step. Hot-rod phantom was acquired at 10°C, 25°C and 40°C. The energy resolution was degraded from 14% to 30% as the temperature raised. The photo-peak position the coincidence count rates were respectively decreased from 1314 ch to 560 ch, from 2.5 kcps to 0.9 kcps as the temperature raised. When the energy window was adjusted to the photo-peak position, the rates were stable from 10°C to 35°C. In hot-rod phantom images acquired at 10°C and 25°C, the rods down to a diameter of 3.5 mm were clearly resolved. However the phantom image acquired at 40 °C demonstrated noticeable degradation in image quality. Future study is being conducted to optimize the adjustable window to obtain stable performance of PET system using GAPD as a function of temperature.