Development of a positron-sensitive probe for tumor detection

对于使用F-18-FDG的肿瘤放射引导手术，检测从身体其他部位发出的湮灭伽马光子会产生本底辐射计数，并限制其在临床情况下的使用。为了克服这一限制，我们开发了一种具有背景排斥能力的术中正电子探针。正电子探针采用由塑料闪烁体和铋萌发体（BGO）组成的光电探测器。来自正电子发射器（如F-18）的正电子被塑料闪烁体探测到并发射湮灭光子。BGO探测其中一个湮灭光子，而光倍增管（PMT）探测来自两个闪烁体的闪烁光子。这两个闪烁体的衰变时间差用于区分事件是一个真实事件，其中正电子和随后的湮灭光子同时被检测到，还是一个背景事件。在这种结构中，即使在高背景伽马光子通量的环境中，也只能选择性地检测到正电子。空间分辨率为11 mm，全宽半宽（FWHM）距离探测器表面5 mm。F-18点源的测量灵敏度为2.6 cps/kBq，距离探测器表面5mm。在直径20 cm的圆柱形模体表面测量含有37 MBq的F-18溶液时，本底计数率小于0.5cps，而正电子计数率在约6 kcps的范围内几乎呈线性。这些结果表明，我们开发的术中正电子探针对于使用高背景湮灭伽马光子通量的F-18-FDG进行肿瘤放射引导手术是有价值的。

For radio-guided surgery on tumors using F-18-FDG, detection of annihilation gamma photons emanating from other parts of the body produces background radiation counts and limits its use in clinical situations. To overcome this limitation, we have developed an intra-operative positron probe with background-rejection capability. The positron probe uses a phoswich detector composed of a plastic scintillator and a bismuth germinate (BGO). A positron from a positron emitter such as F-18 is detected by the plastic scintillator and emits annihilation photons. The BGO detects one of the annihilation photons while a photo-multiplier tube (PMT) detects scintillation photons from both scintillators. The decay time differences of these two scintillators are used to distinguish whether the event is a true event where a positron, and a following annihilation photon are detected simultaneously, or a background event. In this configuration, only positrons can be selectively detected, even in an environment of high background gamma photon flux. Spatial resolution was 11-mm full width at half maximum (FWHM) 5 mm from the detector surface. Measured sensitivity for the F-18 point source was 2.6 cps/kBq 5 mm from the detector surface. The background count rate was less than 0.5cps for a 20-cm diameter cylindrical phantom containing 37 MBq of F-18 solution measured on the phantom surface, while the positron count rate was almost linear over a range of approximately 6 kcps. These results indicate that our developed intra-operative positron probe is valuable for radio-guided surgery on tumors using F-18-FDG in a high flux of background annihilation gamma photons.