Investigation of cooling structure design for PET detector thermal regulation methods

Abstract

Temperature is an essential factor for stable performance of the positron emission tomography (PET). Some of the PET detector components produce significant heat (e.g. readout integrated circuits) that affects its performance. The temperature alters the breakdown voltage of photodetectors, which in turn affects the gain, cross talk, dark count rate and after-pulsing. One of the thermal regulation methods is to use an air/liquid cooling pipe embedded in a cold plate broadly distributing the temperature to the PC board; the gold vias in the board then conduct the temperature to the other side of the board. This paper concentrates on investigating the temperature distribution from various cooling structure configurations. The simulation software COMSOL was used with heat transfer and pipe flow modules to assess the thermal behavior of the cooling system. Two types of cooling pipe arrangements were simulated; a simple and a more complex curve arrangement. For the cold plates, a ceramic (92 W/m-K) and a thermally conductive plastic (10 W/m-K) were simulated. Full as well as “patchy” gold via configurations were also simulated. The simulation was performed for 300 seconds (real time) and the average and the standard deviation temperature of each SiPM was analyzed. With the complex cooling pipe arrangement, the temperature variation throughout all SiPMs was on average 37.9±5.2% higher for ceramic cold plates. For the cold plate materials, the ceramic showed 33.9±15.4% smaller thermal variation and −1.1±0.6% lower temperature compared to the thermally conductive plastic. The patchy vias resulted in 218.2±74.9% larger thermal variation when compared to the patchy vias. In summary, we have simulated various cooling pipe designs, cold plates and gold via distribution configurations to analyze the temperature variation across a PET detector PC board. The thermally conductive ceramic cold plate with as many vias as possible resulted in the most stable temperature variation.