Development of a positron-sensitive probe for tumor detection

对于使用F-18-FDG对肿瘤进行的无线电引导手术，检测从身体其他部位发出的湮灭伽马光子产生背景辐射计数，并限制其在临床情况下的使用。为了克服这一局限性，我们开发了一种具有背景排斥能力的术中正电子探针。正电子探测器使用由塑料闪烁体和锗酸铋（BGO）组成的phoswich探测器。来自正电子发射体（例如F-18）的正电子由塑料闪烁体检测并发射湮灭光子。BGO探测其中一个湮灭光子，而光电倍增管（PMT）探测来自两个湮灭器的闪烁光子。这两个湮灭子的衰变时间差被用来区分事件是否是一个真正的事件，其中一个正电子和一个随后的湮灭光子被同时探测到，或者是一个背景事件。在这种配置中，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毫米半高宽（FWHM）5毫米，从探测器表面。F-18点源的测量灵敏度为2.6 cps/kBq 5 mm的探测器表面。对于直径为20 cm的圆柱体模，在体模表面上测量的含有37 MBq F-18溶液的背景计数率小于0.5cps，而正电子计数率在约6 kcps的范围内几乎是线性的。这些结果表明，我们开发的术中正电子探针是有价值的放射性导向手术肿瘤使用F-18-FDG在高通量的背景湮没伽玛光子。

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.