Count rate capability considerations and results for a positron emission tomograph

Factors which affect count-rate characteristics for a positron emission tomograph (PET) were investigated using a model based on the data acquisition system for a direct slice using Headtome IV. Object size and geometrical design were found to affect the count-rate capability. Low efficiency or low packing fraction of the scintillator degraded the count rate. Thinner slice thickness, larger ring diameter, and shorter length of the slice shield seriously degraded the count rate, and the true-to-single ratio was inversely proportional to each of them. The electronics had relatively small affect compared with the affect of geometrical design. Predominant electronics factors were the deadtimes of the group encoder and the coincidence circuit, while the effect of time window was insignificant. It is concluded that to obtain a better count rate, higher efficiency, larger slice thickness, smaller detector ring diameter, and longer slice shield are desirable as well as minimization of the deadtime of the system when designing a PET.<
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