Marcinkowski Radosław, Mollet Pieter, Van Holen Roel, Vandenberghe Stefaan
Phys Med Biol. 2016 Mar 7;61(5):2196-2212. doi: 10.1088/0031-9155/61/5/2196.
The mouse model is widely used in a vast range of biomedical and preclinical studies. Thanks to the ability to detect and quantify biological processes at the molecular level in vivo, PET has become a well-established tool in these investigations. However, the need to visualize and quantify radiopharmaceuticals in anatomic structures of millimetre or less requires good spatial resolution and sensitivity from small-animal PET imaging systems.In previous work we have presented a proof-of-concept of a dedicated high-resolution small-animal PET scanner based on thin monolithic scintillator crystals and Digital Photon Counter photosensor. The combination of thin monolithic crystals and MLE positioning algorithm resulted in an excellent spatial resolution of 0.7 mm uniform in the entire field of view (FOV). However, the limitation of the scanner was its low sensitivity due to small thickness of the lutetium-yttrium oxyorthosilicate (LYSO) crystals (2 mm).Here we present an improved detector design for a small-animal PET system that simultaneously achieves higher sensitivity and sustains a sub-millimetre spatial resolution. The proposed detector consists of a 5 mm thick monolithic LYSO crystal optically coupled to a Digital Photon Counter. Mean nearest neighbour (MNN) positioning combined with depth of interaction (DOI) decoding was employed to achieve sub-millimetre spatial resolution. To evaluate detector performance the intrinsic spatial resolution, energy resolution and coincidence resolving time (CRT) were measured. The average intrinsic spatial resolution of the detector was 0.60 mm full-width-at-half-maximum (FWHM). A DOI resolution of 1.66 mm was achieved. The energy resolution was 23% FWHM at 511 keV and CRT of 529 ps were measured. The improved detector design overcomes the sensitivity limitation of the previous design by increasing the nominal sensitivity of the detector block and retains an excellent intrinsic spatial resolution.
小鼠模型广泛应用于大量生物医学和临床前研究中。由于能够在体内分子水平检测和量化生物过程，正电子发射断层扫描（PET）已成为这些研究中一种成熟的工具。然而，要在毫米级或更小的解剖结构中可视化和量化放射性药物，需要小动物PET成像系统具备良好的空间分辨率和灵敏度。在之前的工作中，我们展示了一种基于薄型单片闪烁晶体和数字光子计数器光电传感器的专用高分辨率小动物PET扫描仪的概念验证。薄型单片晶体和最大似然估计（MLE）定位算法相结合，在整个视野（FOV）内实现了0.7毫米的出色均匀空间分辨率。然而，该扫描仪的局限性在于，由于硅酸钇镥（LYSO）晶体厚度较小（2毫米），其灵敏度较低。
在此，我们提出一种用于小动物PET系统的改进探测器设计，该设计同时实现了更高的灵敏度并保持亚毫米级空间分辨率。所提出的探测器由一块5毫米厚的单片LYSO晶体与一个数字光子计数器光学耦合而成。采用最近邻平均（MNN）定位与相互作用深度（DOI）解码相结合的方法来实现亚毫米级空间分辨率。为了评估探测器性能，测量了其固有空间分辨率、能量分辨率和符合分辨时间（CRT）。探测器的平均固有空间分辨率为半高宽（FWHM）0.60毫米。实现了1.66毫米的DOI分辨率。在511 keV时能量分辨率为FWHM 23%，并测量得到CRT为529皮秒。改进后的探测器设计通过提高探测器模块的标称灵敏度克服了先前设计的灵敏度限制，并保持了出色的固有空间分辨率。
