Borghi Giacomo, Peet Bart Jan, Tabacchini Valerio, Schaart Dennis R
Phys Med Biol. 2016 Jul 7;61(13):4929-49. doi: 10.1088/0031-9155/61/13/4929. Epub 2016 Jun 10.
New applications for positron emission tomography (PET) and combined PET/magnetic resonance imaging (MRI) are currently emerging, for example in the fields of neurological, breast, and pediatric imaging. Such applications require improved image quality, reduced dose, shorter scanning times, and more precise quantification. This can be achieved by means of dedicated scanners based on ultrahigh-performance detectors, which should provide excellent spatial resolution, precise depth-of-interaction (DOI) estimation, outstanding time-of-flight (TOF) capability, and high detection efficiency. Here, we introduce such an ultrahigh-performance TOF/DOI PET detector, based on a 32 mm × 32 mm × 22 mm monolithic LYSO:Ce crystal. The 32 mm × 32 mm front and back faces of the crystal are coupled to a digital photon counter (DPC) array, in so-called dual-sided readout (DSR) configuration. The fully digital detector offers a spatial resolution of 1.1 mm full width at half maximum (FWHM)/1.2 mm mean absolute error, together with a DOI resolution of ~2.4 mm FWHM, an energy resolution of 10.2% FWHM, and a coincidence resolving time of 147 ps FWHM. The time resolution closely approaches the best results (135 ps FWHM) obtained to date with small crystals made from the same material coupled to the same DPC arrays, illustrating the excellent correction for optical and electronic transit time spreads that can be achieved in monolithic scintillators using maximum-likelihood techniques for estimating the time of interaction. The performance barely degrades for events with missing data (up to 6 out of 32 DPC dies missing), permitting the use of almost all events registered under realistic acquisition conditions. Moreover, the calibration procedures and computational methods used for position and time estimation follow recently made improvements that make them fast and practical, opening up realistic perspectives for using DSR monolithic scintillator detectors in TOF-PET and TOF-PET/MRI systems.
正电子发射断层扫描（PET）以及PET与磁共振成像（MRI）联用的新应用目前正在兴起，例如在神经、乳腺和儿科成像领域。此类应用需要提高图像质量、降低剂量、缩短扫描时间并实现更精确的定量分析。这可以通过基于超高性能探测器的专用扫描仪来实现，这种扫描仪应具备出色的空间分辨率、精确的相互作用深度（DOI）估计、卓越的飞行时间（TOF）能力以及高探测效率。在此，我们介绍一种基于32毫米×32毫米×22毫米整块式LYSO:Ce晶体的超高性能TOF/DOI PET探测器。晶体32毫米×32毫米的正面和背面以所谓的双面读出（DSR）配置耦合到数字光子计数器（DPC）阵列。这种全数字探测器的空间分辨率约为半高宽（FWHM）1.1毫米/平均绝对误差约1.2毫米，DOI分辨率约为FWHM 2.4毫米，能量分辨率为FWHM 10.2%，符合时间分辨率为FWHM 147皮秒。该时间分辨率接近迄今为止使用与相同DPC阵列耦合的相同材料制成的小晶体所获得的最佳结果（FWHM 135皮秒），这表明使用最大似然技术估计相互作用时间，在整块式闪烁体中可以实现对光和电子传输时间扩展的出色校正。对于有缺失数据的事件（32个DPC芯片中最多6个缺失），性能几乎不会下降，这使得在实际采集条件下记录的几乎所有事件都能得到利用。此外，用于位置和时间估计的校准程序和计算方法采用了最近的改进，使其快速且实用，为在TOF-PET和TOF-PET/MRI系统中使用DSR整块式闪烁体探测器开辟了现实前景。
