Liu Zheng, Niu Ming, Kuang Zhonghua, Ren Ning, Wu San, Cong Longhan, Wang Xiaohui, Sang Ziru, Williams Crispin, Yang Yongfeng
Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China.
European Centre for Nuclear Research (CERN), Geneva, Switzerland.
EJNMMI Phys. 2022 Apr 21;9(1):29. doi: 10.1186/s40658-022-00460-4.
Most current whole-body positron emission tomography (PET) scanners use detectors with high timing resolution to measure the time-of-flight of two 511 keV photons, improving the signal-to-noise ratio of PET images. However, almost all current whole-body PET scanners use detectors without depth-encoding capability; therefore, their spatial resolution can be affected by the parallax effect.
In this work, four depth-encoding detectors consisting of LYSO arrays with crystals of 2.98 × 2.98 × 20 mm, 2.98 × 2.98 × 30 mm, 1.95 × 1.95 × 20 mm, and 1.95 × 1.95 × 30 mm, respectively, were read at both ends, with 6 × 6 mm silicon photomultiplier (SiPM) pixels in a 4 × 4 array being used. The timing signals of the detectors were processed individually using an ultrafast NINO application-specific integrated circuit (ASIC) to obtain good timing resolution. The 16 energy signals of the SiPM array were read using a row and column summing circuit to obtain four position-encoding energy signals.
The four PET detectors provided good flood histograms in which all crystals could be clearly resolved, the crystal energy resolutions measured being 10.2, 12.1, 11.4 and 11.7% full width at half maximum (FWHM), at an average crystal depth of interaction (DOI) resolution of 3.5, 3.9, 2.7, and 3.0 mm, respectively. The depth dependence of the timing of each SiPM was measured and corrected, the timing of the two SiPMs being used as the timing of the dual-ended readout detector. The four detectors provided coincidence time resolutions of 180, 214, 239, and 263 ps, respectively.
The timing resolution of the dual-ended readout PET detector was approximately 20% better than that of the single-ended readout detector using the same LYSO array, SiPM array, and readout electronics. The detectors developed in this work used long crystals with small cross-sections and provided good flood histograms, DOI, energy, and timing resolutions, suggesting that they could be used to develop whole-body PET scanners with high sensitivity, uniform high spatial resolution, and high timing resolution.
目前大多数全身正电子发射断层扫描（PET）扫描仪使用具有高时间分辨率的探测器来测量两个511keV光子的飞行时间，从而提高PET图像的信噪比。然而，几乎所有当前的全身PET扫描仪都使用不具备深度编码能力的探测器；因此，它们的空间分辨率会受到视差效应的影响。
在本研究中，制作了四个深度编码探测器，分别由尺寸为2.98×2.98×20mm、2.98×2.98×30mm、1.95×1.95×20mm和1.95×1.95×30mm的LYSO晶体阵列组成，探测器两端均进行读取，采用4×4阵列中6×6mm的硅光电倍增管（SiPM）像素。探测器的定时信号使用超快NINO专用集成电路（ASIC）单独处理，以获得良好的定时分辨率。SiPM阵列的16个能量信号通过行和列求和电路读取，以获得四个位置编码能量信号。
这四个PET探测器提供了良好的泛洪直方图，其中所有晶体都能清晰分辨，测量得到的晶体能量分辨率在半高宽（FWHM）处分别为10.2%、12.1%、11.4%和11.7%，平均晶体相互作用深度（DOI）分辨率分别为3.5mm、3.9mm、2.7mm和3.0mm。测量并校正了每个SiPM定时的深度依赖性，将两个SiPM的定时用作双端读出探测器的定时。这四个探测器的符合时间分辨率分别为180ps、214ps、239ps和263ps。
使用相同的LYSO阵列、SiPM阵列和读出电子设备时，双端读出PET探测器的定时分辨率比单端读出探测器大约高20%。本研究中开发的探测器使用了小横截面的长晶体，并提供了良好的泛洪直方图、DOI、能量和定时分辨率，表明它们可用于开发具有高灵敏度、均匀高空间分辨率和高定时分辨率的全身PET扫描仪。
