Liu Zheng, Mungai Samuel, Kuang Zhonghua, Ren Ning, Xie Siwei, Peng Qiyu, Williams Crispin, Yang Yongfeng
Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China.
Institute of Biomedical Engineering, Shenzhen Bay Laboratory, Shenzhen, China.
Med Phys. 2025 Feb;52(2):867-879. doi: 10.1002/mp.17544. Epub 2024 Nov 28.
An organ-specific Positron emission tomography (PET) scanner can achieve the same sensitivity with much fewer detectors as compared to a whole-body PET scanner, thereby substantially reducing the system cost. It can also achieve much better spatial resolution as compared to a whole-body PET scanner since the photon noncollinearity effect is reduced by using smaller detector ring diameter. Consequently, the development of organ-specific PET scanners with high spatial resolution, high sensitivity, and low cost has been a major focus of international research in PET instrument development for many years.
The focus of this work is to develop high-resolution depth encoding PET detectors with high timing resolution and a reduced number of signal processing electronic channels. Consequently, PET scanners tailored for specific organs can be developed with high spatial and timing resolutions, enhanced sensitivity, and affordable cost.
An 8 × 8 silicon photomultiplier (SiPM) array with a pixel size of 3 × 3 mm and a multiplexed signal readout circuit is coupled to one end of the lutetium yttrium orthosilicate (LYSO) array with a glass light guide between them to achieve a good crystal identification of small crystals by using only four position-encoding energy signals. A 4 × 4 SiPM array with a pixel size of 6 × 6 mm and an individual readout circuit is coupled to the other end of the crystal array without a light guide to achieve a good coincidence timing resolution (CTR). The depth of interaction (DOI) of the detector is measured by ratio of the energies measured by the two SiPM arrays and can be used to correct the depth dependency of the timing. The flood histograms, energy resolutions (ERs), DOI resolutions, and CTRs of two detectors utilizing LYSO arrays with different crystal sizes were measured with each of the two SiPM arrays alternately placed at the front of the detectors.
A better flood histogram was obtained by placing the 8 × 8 SiPM array in front of the detector. The depth dependency of timing was larger when the 4 × 4 SiPM array was placed at the front of the detector. A better CTR was obtained by placing the 4 × 4 SiPM array at the back of the detector as compared to placing it at the front of the detector if the depth-dependent timing correction was not performed. If the depth-dependent timing correction was performed, a better CTR can be obtained by placing the 4 × 4 SiPM array at the front of the detector. The first detector using a 12 × 12 LYSO crystal array with a crystal size of 1.95 × 1.95 × 20 mm provided a flood histogram with all crystals clearly resolved, an ER of 11.7%, a DOI resolution of 2.9 mm, and a CTR of 275 ps with the depth-dependent timing correction. The second detector using a 23 × 23 LYSO crystal array with a crystal size of 0.95 × 0.95 × 20 mm provided a flood histogram with all but the edge crystals clearly resolved, an ER of 17.6%, a DOI resolution of 2.3 mm, and a CTR of 293 ps with the depth-dependent timing correction.
PET detectors with small crystal cross-sectional sizes, good DOI and timing resolutions and a reduced number of electronics channels were developed. The detectors can be used to develop high performance organ-specific PET scanners.
与全身正电子发射断层扫描（PET）扫描仪相比，器官特异性PET扫描仪使用少得多的探测器就能实现相同的灵敏度，从而大幅降低系统成本。由于使用较小的探测器环直径可减少光子非共线性效应，与全身PET扫描仪相比，它还能实现更好的空间分辨率。因此，多年来，开发具有高空间分辨率、高灵敏度和低成本的器官特异性PET扫描仪一直是PET仪器开发领域国际研究的主要重点。
这项工作的重点是开发具有高时间分辨率和减少信号处理电子通道数量的高分辨率深度编码PET探测器。因此，可以开发针对特定器官的PET扫描仪，使其具有高空间和时间分辨率、更高的灵敏度以及可承受的成本。
将一个像素尺寸为3×3毫米的8×8硅光电倍增管（SiPM）阵列和一个多路复用信号读出电路耦合到硅酸镥钇（LYSO）阵列的一端，它们之间有一个玻璃光导，通过仅使用四个位置编码能量信号来实现对小晶体的良好晶体识别。将一个像素尺寸为6×6毫米的4×4 SiPM阵列和一个单独读出电路耦合到晶体阵列的另一端，不使用光导，以实现良好的符合时间分辨率（CTR）。探测器的相互作用深度（DOI）通过两个SiPM阵列测量的能量之比来测量，并可用于校正时间的深度依赖性。使用不同晶体尺寸的LYSO阵列的两个探测器的泛光直方图、能量分辨率（ER）、DOI分辨率和CTR，通过将两个SiPM阵列交替放置在探测器前端进行测量。
将8×8 SiPM阵列放置在探测器前端可获得更好的泛光直方图。当4×4 SiPM阵列放置在探测器前端时，时间的深度依赖性更大。与不进行深度依赖性时间校正时将4×4 SiPM阵列放置在探测器前端相比，将其放置在探测器后端可获得更好的CTR。如果进行深度依赖性时间校正，将4×4 SiPM阵列放置在探测器前端可获得更好的CTR。第一个探测器使用尺寸为1.95×1.95×20毫米的12×12 LYSO晶体阵列，经深度依赖性时间校正后，提供了一个所有晶体都清晰分辨的泛光直方图，ER为11.
