Thermal management proposal for a low-profile positron emission tomography fully pixelated front-end for submillimetric resolution MRI compatible insert dedicated to small animals

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Accelerators, spectrometers, detectors and associated equipment, 2020-06, Vol.966, p.163848, Article 163848
• Main Authors: Espagnet, Romain, Bouchard, Jonathan, Moghadam, Narjes, Samson, Arnaud, Lakhssassi, Ahmed, Lecomte, Roger, Fontaine, Réjean
• Format: Article
• Language: English
• Subjects: Flow Simulation; Low-profile PET front-end; Positron emission tomography (PET); Thermal management
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/j.nima.2020.163848

The LabPET II is a positron emission tomography technology platform developed for high resolution imaging of small and mid-sized animals. In its original configuration, the electronics includes many printed circuit boards assembled with right angle connectors creating cavities difficult to cool down by air convection. To alleviate this problem and also to reduce the required space radially, a new low-profile electronic architecture is developed. It consists of a Carrier Board on which four printed circuit interposers, based on a ball grid array technology, are soldered. The aim of this work is to study different thermal management scenarios for a PET insert based on this new LabPET II low-profile electronics. A prototype assembly of 12 carrier boards was developed with the thermal model of the LabPET II ASIC built in the Flow Simulation module of SolidWorks. First, a thermal comparison between the typical LabPET II scanner and the simulated low-profile prototype was performed in similar conditions. Second, simulations were used to evaluate three thermal management approaches on the scanner with low-profile electronics: no thermal management, forced airflow (with a fan) and water-cooling. In the latter, three simulations were conducted to maintain the top face of the heat sink located on the carrier board at temperatures of 15, 20 or 30 degrees Celsius. The comparison between the original LabPET II and a scanner with low-profile electronics has shown an ASIC mean temperature of 55 degrees Celsius and 40 degrees Celsius, respectively. In the exploration studies, without any thermal management, the ASIC temperature reached up to 205 degrees Celsius. With an airflow, created with a fan blowing air axially on the extremity of the heatsinks outside the FoV, the ASIC temperature decreases below 100 degrees Celsius. With an applied surface condition of 15 degrees Celsius on the heat sinks extremity parts, the ASIC maximum temperature is 65 degrees Celsius. When surface conditions of 20 and 30 degrees Celsius are applied on the top of the heat sink, the ASIC temperature is reduced to 28 and 38 degrees Celsius, respectively. The new low-profile architecture demonstrates that heat sinks with a simple water-cooling solution reduce the temperature down to 25 degrees Celsius, a real improvement compared to the 55 degrees in the current LabPET II architecture. This improvement will be useful inside an MRI system where eddy currents are induced in all conductive structure