Department of Nuclear Medicine, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH, 44195, USA.
Med Phys. 2017 Aug;44(8):4230-4238. doi: 10.1002/mp.12379. Epub 2017 Jun 30.
Tri-PET refers to high-resolution 511-keV emission tomography using a multipinhole collimator in conjunction with lower resolution PET detectors operating in coincidence mode. Tri-PET is unique in that three spatial locations are associated with each event (two detector coordinates and one pinhole location). Spatial resolution and sensitivity are similar to that of 511-keV SPECT and are governed mainly by the collimator design. However because of a third spatial location in Tri-PET, the line-of-response is overdetermined. This feature permits new opportunities in data processing which impact collimator design. In particular, multiplexing can be avoided since the coincidence data identify the pinhole through which the photon passed. In this paper, the principles of Tri-PET collimator design are reviewed and then applied to the case of high-resolution imaging of a small animal in a clinical PET scanner.
The design of a 148-pinhole collimator for whole-body imaging of a mouse is presented. Two pinhole designs were investigated: knife-edge pinholes with 1.1 mm aperture and novel hyperboloidal pinholes with 1.2 mm aperture, both having 18° cone angle. The pinhole configuration is unfocused, covering a whole-body mouse field of view with nearly uniform sensitivity. Computer simulations were performed of a micro hot rods phantom imaged with this collimator in a clinical PET scanner. Sensitivity was estimated by simulating a point source centered on-axis at locations spanning a 70-mm axial range, similar to the NEMA NU-4 standard for whole-body mouse imaging.
Reconstructed images of the hot rods phantom demonstrated the ability to resolve 1.1 mm structures with the knife-edge pinholes and 1.0 mm structures with the hyperboloidal pinholes. Sensitivity was found to be 0.093% and 0.054% for the knife-edge and hyperboloidal pinholes, respectively.
With a properly designed multipinhole collimator, high-resolution and acceptable sensitivity are achievable with Tri-PET using ordinary clinical PET detectors.
Tri-PET 是指使用多针孔准直器结合以较低分辨率工作的符合探测 PET 探测器进行的 511keV 发射断层成像。Tri-PET 的独特之处在于每个事件都与三个空间位置相关联（两个探测器坐标和一个针孔位置）。空间分辨率和灵敏度与 511keV SPECT 相似，主要由准直器设计决定。然而，由于 Tri-PET 中有第三个空间位置，响应线是过度确定的。这一特性为数据处理带来了新的机会，从而影响了准直器的设计。特别是，由于符合数据可以识别光子穿过的针孔，因此可以避免复用。本文回顾了 Tri-PET 准直器设计的原理，然后将其应用于在临床 PET 扫描仪中对小动物进行高分辨率成像的情况。
提出了一种用于对小鼠进行全身成像的 148 针孔准直器的设计。研究了两种针孔设计：具有 1.1mm 孔径的刀刃状针孔和具有 1.2mm 孔径的新型双曲面针孔，两者的锥角均为 18°。该针孔配置为非聚焦型，覆盖整个小鼠体视场，灵敏度几乎均匀。在临床 PET 扫描仪中使用该准直器对微热棒体模进行了计算机模拟。通过模拟位于轴向范围跨越 70mm 的轴上位置的点源，估计灵敏度，类似于用于全身小鼠成像的 NEMA NU-4 标准。
用刀刃状针孔重建的热棒体模图像显示出分辨 1.1mm 结构的能力，用双曲面针孔可分辨 1.0mm 结构。分别发现刀刃状针孔和双曲面针孔的灵敏度为 0.093%和 0.054%。
使用适当设计的多针孔准直器，使用普通临床 PET 探测器可以实现 Tri-PET 的高分辨率和可接受的灵敏度。
