Institute of Biomedical Engineering, Shenzhen Bay Laboratory, Shenzhen, China.
Peking University Shenzhen Graduate School, Shenzhen, China.
Med Phys. 2024 Oct;51(10):7140-7152. doi: 10.1002/mp.17313. Epub 2024 Jul 20.
Monolithic or semi-monolithic detectors are attractive for positron emission tomography (PET) scanners with depth-of-interaction (DOI) capability. However, they often require complicated calibrations to determine the interaction positions of gamma photons.
We introduce a novel hybrid detector design that combines pixelated and semi-monolithic elements to achieve DOI capability while simplifying the calibrations for positioning.
A prototype detector with eight hybrid lutetium-yttrium oxyorthosilicate (LYSO) layers having dimensions of 25.8 × 12.9 × 15 mm was constructed. The energy-weighted and energy-squared weighted averages were used for estimating the x- (pixelated direction) and y-positions (non-pixelated direction). Pseudo-pixels were defined as discrete areas on the flood image based on the crystal look-up table (LUT). The intrinsic spatial resolutions in the pixelated and non-pixelated directions were measured. The ratio of the maximum to the sum of the multipixel photon counter (MPPC) signals was used to estimate the DOI positions. The coincidence timing resolution (CTR) was measured using the average and energy-weighted average of the earliest n time stamps. Two energy windows of 250-700 and 400-600 keV were applied for the measurements.
The pattern of the flood images showed discrete event clusters, demonstrating that simple calibrations for determining the x- and y-positions of events could be achieved. Under 400-600 keV energy window, the average intrinsic spatial resolutions were 1.15 and 1.34 mm for the pixelated and non-pixelated directions; the average DOI resolution of the second row of pseudo-pixels was 5.1 mm in full width at half maximum (FWHM); when using the energy-weighted average of the earliest four-time stamps, the best CTR of 350 ps was achieved. Applying a broader energy window of 250-700 keV only slightly degrades the DOI resolution while maintaining the intrinsic resolution; the best CTR degrades to 410 ps.
The proposed hybrid detector concept was verified, and a prototype detector showed high performance for 3D positioning and timing resolution. The novel detector concept shows promise for preclinical and clinical PET scanners with DOI capability.
对于具有相互作用深度（DOI）能力的正电子发射断层扫描（PET）扫描仪，整体式或半整体式探测器具有吸引力。然而，它们通常需要复杂的校准来确定伽马光子的相互作用位置。
我们引入了一种新的混合探测器设计，该设计结合了像素化和半整体式元件，在简化定位校准的同时实现了 DOI 能力。
构建了一个具有八个混合硅酸镥（LYSO）层的原型探测器，尺寸为 25.8×12.9×15mm。能量加权和能量平方加权平均值用于估计 x 位置（像素化方向）和 y 位置（非像素化方向）。根据晶体查找表（LUT），在洪水图像上定义伪像素作为离散区域。测量像素化和非像素化方向的固有空间分辨率。使用多像素光子计数器（MPPC）信号的最大值与和的比值来估计 DOI 位置。使用最早 n 个时间戳的平均值和能量加权平均值测量符合时间分辨率（CTR）。应用了 250-700keV 和 400-600keV 两个能量窗口进行测量。
洪水图像的图案显示出离散的事件簇，表明可以实现简单的校准来确定事件的 x 和 y 位置。在 400-600keV 能量窗口下，像素化和非像素化方向的平均固有空间分辨率分别为 1.15mm 和 1.34mm；第二行伪像素的平均 DOI 分辨率为 5.1mm 全宽半最大值（FWHM）；使用最早四个时间戳的能量加权平均值时，实现了最佳的 350ps CTR。应用更宽的 250-700keV 能量窗口仅略微降低 DOI 分辨率，同时保持固有分辨率；最佳 CTR 降至 410ps。
验证了所提出的混合探测器概念，原型探测器在 3D 定位和定时分辨率方面表现出高性能。新型探测器概念有望用于具有 DOI 能力的临床前和临床 PET 扫描仪。
