Lee Min Sun, Kim Kyeong Yun, Ko Guen Bae, Lee Jae Sung
Department of Nuclear Medicine, College of Medicine, Seoul National University, Seoul, Republic of Korea. Interdisciplinary Program in Radiation Applied Life Science, Seoul National University, Seoul, Republic of Korea.
Phys Med Biol. 2017 May 21;62(10):3983-3996. doi: 10.1088/1361-6560/aa64c7. Epub 2017 Apr 13.
In this study, we developed a proof-of-concept prototype PET system using a pair of depth-of-interaction (DOI) PET detectors based on the proposed DOI-encoding method and digital silicon photomultiplier (dSiPM). Our novel cost-effective DOI measurement method is based on a triangular-shaped reflector that requires only a single-layer pixelated crystal and single-ended signal readout. The DOI detector consisted of an 18 × 18 array of unpolished LYSO crystal (1.47 × 1.47 × 15 mm) wrapped with triangular-shaped reflectors. The DOI information was encoded by depth-dependent light distribution tailored by the reflector geometry and DOI correction was performed using four-step depth calibration data and maximum-likelihood (ML) estimation. The detector pair and the object were placed on two motorized rotation stages to demonstrate 12-block ring PET geometry with 11.15 cm diameter. Spatial resolution was measured and phantom and animal imaging studies were performed to investigate imaging performance. All images were reconstructed with and without the DOI correction to examine the impact of our DOI measurement. The pair of dSiPM-based DOI PET detectors showed good physical performances respectively: 2.82 and 3.09 peak-to-valley ratios, 14.30% and 18.95% energy resolution, and 4.28 and 4.24 mm DOI resolution averaged over all crystals and all depths. A sub-millimeter spatial resolution was achieved at the center of the field of view (FOV). After applying ML-based DOI correction, maximum 36.92% improvement was achieved in the radial spatial resolution and a uniform resolution was observed within 5 cm of transverse PET FOV. We successfully acquired phantom and animal images with improved spatial resolution and contrast by using the DOI measurement. The proposed DOI-encoding method was successfully demonstrated in the system level and exhibited good performance, showing its feasibility for animal PET applications with high spatial resolution and sensitivity.
在本研究中，我们基于所提出的深度交互（DOI）编码方法和数字硅光电倍增管（dSiPM），开发了一种概念验证原型PET系统。我们新颖且经济高效的DOI测量方法基于一个三角形反射器，该反射器仅需要单层像素化晶体和单端信号读出。DOI探测器由一个18×18阵列的未抛光LYSO晶体（1.47×1.47×15毫米）组成，晶体包裹着三角形反射器。DOI信息通过由反射器几何形状定制的深度相关光分布进行编码，并且使用四步深度校准数据和最大似然（ML）估计进行DOI校正。探测器对和物体放置在两个电动旋转台上，以展示直径为11.15厘米的12块环PET几何结构。测量了空间分辨率，并进行了体模和动物成像研究以研究成像性能。所有图像在有和没有DOI校正的情况下进行重建，以检查我们的DOI测量的影响。基于dSiPM的DOI PET探测器对分别表现出良好的物理性能：峰谷比分别为2.82和3.09，能量分辨率分别为14.30%和18.95%，并且在所有晶体和所有深度上平均DOI分辨率为4.28和4.24毫米。在视野（FOV）中心实现了亚毫米空间分辨率。应用基于ML的DOI校正后，径向空间分辨率最大提高了36.92%，并且在横向PET FOV的5厘米范围内观察到均匀的分辨率。通过使用DOI测量，我们成功获取了具有改进的空间分辨率和对比度的体模和动物图像。所提出的DOI编码方法在系统层面上得到了成功验证，并表现出良好的性能，显示了其在高空间分辨率和灵敏度的动物PET应用中的可行性。
