Department of Electronic Engineering, Sogang University, 1 Shinsu-Dong, Mapo-Gu, Seoul 121-742, South Korea.
Med Phys. 2013 Apr;40(4):042503. doi: 10.1118/1.4793754.
The aim of this study was to develop a prototype magnetic resonance (MR)-compatible positron emission tomography (PET) that can be inserted into a MR imager and that allows simultaneous PET and MR imaging of the human brain. This paper reports the initial results of the authors' prototype brain PET system operating within a 3-T magnetic resonance imaging (MRI) system using newly developed Geiger-mode avalanche photodiode (GAPD)-based PET detectors, long flexible flat cables, position decoder circuit with high multiplexing ratio, and digital signal processing with field programmable gate array-based analog to digital converter boards.
A brain PET with 72 detector modules arranged in a ring was constructed and mounted in a 3-T MRI. Each PET module was composed of cerium-doped lutetium yttrium orthosilicate (LYSO) crystals coupled to a tileable GAPD. The GAPD output charge signals were transferred to preamplifiers using 3 m long flat cables. The LYSO and GAPD were located inside the MR bore and all electronics were positioned outside the MR bore. The PET detector performance was investigated both outside and inside the MRI, and MR image quality was evaluated with and without the PET system.
The performance of the PET detector when operated inside the MRI during MR image acquisition showed no significant change in energy resolution and count rates, except for a slight degradation in timing resolution with an increase from 4.2 to 4.6 ns. Simultaneous PET/MR images of a hot-rod and Hoffman brain phantom were acquired in a 3-T MRI. Rods down to a diameter of 3.5 mm were resolved in the hot-rod PET image. The activity distribution patterns between the white and gray matter in the Hoffman brain phantom were well imaged. The hot-rod and Hoffman brain phantoms on the simultaneously acquired MR images obtained with standard sequences were observed without any noticeable artifacts, although MR image quality requires some improvement.
These results demonstrate that the simultaneous acquisition of PET and MR images is feasible using the MR insertable PET developed in this study.
本研究旨在开发一种可插入磁共振成像（MRI）仪的原型磁共振兼容正电子发射断层扫描（PET）系统，以实现人类大脑的 PET 和 MRI 同步成像。本文报告了作者使用新开发的基于盖革模式雪崩光电二极管（GAPD）的 PET 探测器、长柔性扁平电缆、具有高多路复用比的位置解码器电路以及基于现场可编程门阵列的模数转换器板的数字信号处理，在 3T 磁共振成像（MRI）系统中运行的原型脑 PET 系统的初步结果。
构建了一个带有 72 个探测器模块的脑 PET，并将其安装在 3T MRI 中。每个 PET 模块由掺铈硅酸镥（LYSO）晶体与可平铺 GAPD 组成。GAPD 输出电荷信号通过 3m 长的扁平电缆传输到前置放大器。LYSO 和 GAPD 位于 MRI 孔内，所有电子设备位于 MRI 孔外。在 MRI 内外都对 PET 探测器性能进行了研究，并在有无 PET 系统的情况下评估了 MRI 图像质量。
当在 MRI 内进行 MR 图像采集时，PET 探测器的性能除了定时分辨率略有下降（从 4.2ns 增加到 4.6ns）外，在能量分辨率和计数率方面均无明显变化。在 3T MRI 中采集了热棒和霍夫曼脑模型的同时 PET/MR 图像。在热棒 PET 图像中可以分辨出直径为 3.5mm 的棒。霍夫曼脑模型的白质和灰质之间的活性分布模式得到了很好的成像。虽然 MRI 图像质量需要进一步提高，但使用标准序列获得的同时采集的 MRI 上的热棒和霍夫曼脑模型可以观察到，没有明显的伪影。
这些结果表明，使用本研究中开发的可插入式磁共振 PET 可以实现 PET 和 MRI 的同步采集。
