Düppenbecker Peter M, Weissler Bjoern, Gebhardt Pierre, Schug David, Wehner Jakob, Marsden Paul K, Schulz Volkmar
Imaging Sciences & Biomedical Engineering, King's College London, UK.
Department of Physics of Molecular Imaging Systems, Institute of Experimental Molecular Imaging, RWTH Aachen University, Aachen, DE.
Biomed Phys Eng Express. 2016 Feb;2(1):015010. doi: 10.1088/2057-1976/2/1/015010. Epub 2016 Feb 4.
Advances in solid-state photon detectors paved the way to combine positron emission tomography (PET) and magnetic resonance imaging (MRI) into highly integrated, truly simultaneous, hybrid imaging systems. Based on the most recent digital SiPM technology, we developed an MRI-compatible PET detector stack, intended as a building block for next generation simultaneous PET/MRI systems. Our detector stack comprises an array of 8 × 8 digital SiPM channels with 4 mm pitch using Philips Digital Photon Counting DPC 3200-22 devices, an FPGA for data acquisition, a supply voltage control system and a cooling infrastructure. This is the first detector design that allows the operation of digital SiPMs simultaneously inside an MRI system. We tested and optimized the MRI-compatibility of our detector stack on a laboratory test bench as well as in combination with a Philips Achieva 3 T MRI system. Our design clearly reduces distortions of the static magnetic field compared to a conventional design. The MRI static magnetic field causes weak and directional drift effects on voltage regulators, but has no direct impact on detector performance. MRI gradient switching initially degraded energy and timing resolution. Both distortions could be ascribed to voltage variations induced on the bias and the FPGA core voltage supply respectively. Based on these findings, we improved our detector design and our final design shows virtually no energy or timing degradations, even during heavy and continuous MRI gradient switching. In particular, we found no evidence that the performance of the DPC 3200-22 digital SiPM itself is degraded by the MRI system.
固态光子探测器的进展为将正电子发射断层扫描（PET）和磁共振成像（MRI）结合成高度集成、真正同时工作的混合成像系统铺平了道路。基于最新的数字硅光电倍增管（SiPM）技术，我们开发了一种与MRI兼容的PET探测器堆栈，旨在作为下一代同时PET/MRI系统的一个组件。我们的探测器堆栈包括一个由8×8个数字SiPM通道组成的阵列，通道间距为4毫米，采用飞利浦数字光子计数DPC 3200-22器件，一个用于数据采集的现场可编程门阵列（FPGA），一个电源电压控制系统和一个冷却基础设施。这是第一种允许数字SiPM在MRI系统内部同时运行的探测器设计。我们在实验室试验台上以及与飞利浦Achieva 3T MRI系统结合使用时，对探测器堆栈的MRI兼容性进行了测试和优化。与传统设计相比，我们的设计明显减少了静磁场的畸变。MRI静磁场对电压调节器会产生微弱的定向漂移效应，但对探测器性能没有直接影响。MRI梯度切换最初会降低能量和时间分辨率。这两种畸变分别归因于偏置电压和FPGA核心电源电压上感应出的电压变化。基于这些发现，我们改进了探测器设计，我们的最终设计即使在频繁且持续的MRI梯度切换过程中，也几乎没有能量或时间分辨率的下降。特别是，我们没有发现证据表明DPC 3200-22数字SiPM本身的性能会因MRI系统而下降。
