Feasibility of a brain-dedicated PET-MRI system using four-layer DOI detectors integrated with an RF head coil
Feasibility of a brain-dedicated PET-MRI system using four-layer DOI detectors integrated with an RF head coil
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DOI：
10.1016/j.nima.2014.04.034
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发表时间：
2014-08
影响因子：
1.4
通讯作者：
F. Nishikido;T. Obata;K. Shimizu;M. Suga;N. Inadama;A. Tachibana;E. Yoshida;Hiroshi Ito;T. Yama
中科院分区：
文献类型：
--
作者：
F. Nishikido;T. Obata;K. Shimizu;M. Suga;N. Inadama;A. Tachibana;E. Yoshida;Hiroshi Ito;T. Yama
我们正在开发一种PET-MRI系统，该系统由PET探测器与MRI的头部线圈集成在一起，以实现高空间分辨率和高灵敏度的同时测量。在PET-MRI系统中，PET探测器由闪烁体块、光电探测器和具有四层相互作用深度（DOI）编码能力的前端电路组成，被放置在靠近被测对象的位置。因此，所提出的系统可以实现高灵敏度，而不会由于四层DOI能力而导致的视差而导致的视场边缘处的空间分辨率的劣化。在本文中，我们制作了一个原型系统，其中包括一个原型四层DOI-PET探测器，一个虚拟PET探测器和一个原型鸟笼型头部线圈。该系统由六个单片多像素光子计数器（MPPC）阵列（S11064- 050 P）、一块读出电路板、两块闪烁体和一个铜屏蔽盒组成。每个闪烁体块由四层Lu1.8Gd0.2SiO5：Ce（LGSO）闪烁体组成，闪烁晶体之间插入反射体。虚拟探测器具有除两个闪烁体块之外的所有这些组件。头部线圈专用于3.0 T MRI（西门子公司的ESTTOM Verio），两个探测器安装在头部线圈元件之间的间隙中。通过梯度回波和自旋回波方法，在有和没有MRI测量的情况下，对原型四层DOI-PET探测器的能量分辨率和晶体识别性能进行了评估。我们确定了晶体元素在所有四个层的二维洪水直方图和能量分辨率为15-18%的单晶元素在同时测量。所有层的平均能量分辨率和光峰位置之间的差异（有和没有MRI测量）低于0.3个百分点和1.7%。结果表明，这些性能足以作为所提出的PET-MRI系统的PET探测器，并且在同时测量中MRI测量对PET成像没有影响。还在有和没有PET探测器测量的情况下评价了MRI图像的信噪比和MRI的静磁场。由于LGSO增感器，静磁场的最大降低约为1 ppm。信噪比从没有PET探测器的242.80下降到同时测量的44.948。
We are developing a PET-MRI system which consists of PET detectors integrated with the head coil of the MRI in order to realize high spatial resolution and high sensitivity in simultaneous measurements. In the PET-MRI system, the PET detectors which consist of a scintillator block, photo-detectors and front-end circuits with four-layer depth-of-interaction (DOI) encoding capability are placed close to the measured object. Therefore, the proposed system can achieve high sensitivity without degradation of spatial resolution at the edge of the field-of-view due to parallax error thanks to the four-layer DOI capability. In this paper, we fabricated a prototype system which consists of a prototype four-layer DOI-PET detector, a dummy PET detector and a prototype birdcage type head coil. Then we used the prototype system to evaluate the performance of the four-layer DOI-PET detector and the reciprocal influence between the PET detectors and MRI images.The prototype DOI-PET detector consists of six monolithic multi-pixel photon counter (MPPC) arrays (S11064-050P), a readout circuit board, two scintillator blocks and a copper shielding box. Each scintillator block consists of four layers of Lu1.8Gd0.2SiO5:Ce (LGSO) scintillators and reflectors are inserted between the scintillation crystals. The dummy detector has all these components except the two scintillator blocks. The head coil is dedicated to a 3.0 T MRI (MAGNETOM Verio, Siemens) and the two detectors are mounted in gaps between head coil elements.Energy resolution and crystal identification performance of the prototype four-layer DOI-PET detector were evaluated with and without MRI measurements by the gradient echo and spin echo methods. We identified crystal elements in all four layers from a 2D flood histogram and energy resolution of 15–18% was obtained for single crystal elements in simultaneous measurements. The difference between the average energy resolutions and photo-peak positions with and without MRI measurements was lower than 0.3 percentage points and 1.7% for all layers. The results indicated that these performances were sufficient as PET detectors for the proposed PET-MRI system and there was no influence from the MRI measurements on the PET imaging in the simultaneous measurements. The signal-to-noise ratio of the MRI image and static magnetic field of the MRI were also evaluated with and without measurements of the PET detectors. The maximum decrease of the static magnetic field due to the LGSO scintillators was approximately 1 ppm. The signal-to-noise ratio decreased from 242.80 without the PET detector to 44.948 in simultaneous measurements.