Jung Jin Ho, Choi Yong, Jung Jiwoong, Kim Sangsu, Lim Hyun Keong, Im Ki Chun, Oh Chang Hyun, Park Hyun-wook, Kim Kyung Min, Kim Jong Guk
Department of Electronic Engineering, Sogang University, 35 Baekbeom-ro, Mapo-gu, Seoul 121-742, Korea.
Department of Electrical Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Korea.
Med Phys. 2015 May;42(5):2354-63. doi: 10.1118/1.4918321.
The purpose of this study was to develop a dual-modality positron emission tomography (PET)/magnetic resonance imaging (MRI) with insertable PET for simultaneous PET and MR imaging of the human brain.
The PET detector block was composed of a 4 × 4 matrix of detector modules, each consisting of a 4 × 4 array LYSO coupled to a 4 × 4 Geiger-mode avalanche photodiode (GAPD) array. The PET insert consisted of 18 detector blocks, circularly mounted on a custom-made plastic base to form a ring with an inner diameter of 390 mm and axial length of 60 mm. The PET gantry was shielded with gold-plated conductive fabric tapes with a thickness of 0.1 mm. The charge signals of PET detector transferred via 4 m long flat cables were fed into the position decoder circuit. The flat cables were shielded with a mesh-type aluminum sheet with a thickness of 0.24 mm. The position decoder circuit and field programmable gate array-embedded DAQ modules were enclosed in an aluminum box with a thickness of 10 mm and located at the rear of the MR bore inside the MRI room. A 3-T human MRI system with a Larmor frequency of 123.7 MHz and inner bore diameter of 60 cm was used as the PET/MRI hybrid system. A custom-made radio frequency (RF) coil with an inner diameter of 25 cm was fabricated. The PET was positioned between gradient and the RF coils. PET performance was measured outside and inside the MRI scanner using echo planar imaging, spin echo, turbo spin echo, and gradient echo sequences. MRI performance was also evaluated with and without the PET insert. The stability of the newly developed PET insert was evaluated and simultaneous PET and MR images of a brain phantom were acquired.
No significant degradation of the PET performance caused by MR was observed when the PET was operated using various MR imaging sequences. The signal-to-noise ratio of MR images was slightly degraded due to the PET insert installed inside the MR bore while the homogeneity was maintained. The change of gain of the 256 GAPD/scintillator elements of a detector block was <3% for 60 min, and simultaneous PET and MR images of a brain phantom were successfully acquired.
Experimental results indicate that a compact and lightweight PET insert for hybrid PET/MRI can be developed using GAPD arrays and charge signal transmission method proposed in this study without significant interference.
本研究的目的是开发一种带有可插入式正电子发射断层扫描（PET）的双模态正电子发射断层扫描（PET）/磁共振成像（MRI）系统，用于对人脑进行同步PET和MR成像。
PET探测器模块由一个4×4矩阵的探测器模块组成，每个探测器模块由一个4×4阵列的LYSO晶体耦合到一个4×4盖革模式雪崩光电二极管（GAPD）阵列构成。PET插入件由18个探测器模块组成，呈圆形安装在定制的塑料基座上，形成一个内径为390mm、轴向长度为60mm的环。PET扫描架用厚度为0.1mm的镀金导电织物带进行屏蔽。通过4m长扁平电缆传输的PET探测器的电荷信号被馈入位置解码电路。扁平电缆用厚度为0.24mm的网状铝板进行屏蔽。位置解码电路和嵌入现场可编程门阵列的DAQ模块被封装在一个厚度为10mm的铝盒中，并位于MRI室内MR孔的后部。使用一台拉莫尔频率为123.7MHz、内径为60cm的3T人体MRI系统作为PET/MRI混合系统。制作了一个内径为25cm的定制射频（RF）线圈。PET位于梯度线圈和RF线圈之间。使用回波平面成像、自旋回波、快速自旋回波和梯度回波序列在MRI扫描仪外部和内部测量PET性能。在有和没有PET插入件的情况下也对MRI性能进行了评估。评估了新开发的PET插入件的稳定性，并采集了脑模体的同步PET和MR图像。
当使用各种MR成像序列操作PET时，未观察到MR对PET性能有明显的降解作用。由于PET插入件安装在MR孔内，MR图像的信噪比略有下降，但均匀性得以保持。一个探测器模块的256个GAPD/闪烁体元件的增益在60分钟内变化<3%，并成功采集了脑模体的同步PET和MR图像。
实验结果表明，使用本研究中提出的GAPD阵列和电荷信号传输方法，可以开发出一种用于PET/MRI混合系统的紧凑、轻便的PET插入件且不会产生明显干扰。
