Hoffman E J, Huang S C, Phelps M E, Kuhl D E
J Comput Assist Tomogr. 1981 Jun;5(3):391-400. doi: 10.1097/00004728-198106000-00015.
Accidental coincidences (ACs) and methods of compensation for ACs were investigated in terms of their effect on quantitation in positron emission computed tomography (ECT). Formulations of basic expressions describing the physical factors, which cause true coincidences or ACs, are presented to provide a framework of contrasting the two phenomena. Correction of image data for attenuation of the annihilation radiation or nonuniformities in detector efficiency is shown to amplify errors caused by the presence of ACs in the data. It was shown that failure to compensate for ACs caused overestimates in measurements of isotope concentrations from image data and that in many cases the overestimate was significant for relatively modest percentages of ACs in the data. Three methods of compensation for ACs were evaluated as to their accuracy and effect on statistical noise in images. It was found that nonuniform detector efficiencies could cause prominent image artifacts if an inadequate method was employed in the determination and subtraction of ACs from image data. The additional statistical noise produced in images by subtraction of ACs from total coincidence data demonstrates the advisability of minimizing AC rates in spite of an ability to adequately measure and compensate for their presence in the data.
研究了偶然符合（ACs）及其补偿方法对正电子发射计算机断层扫描（ECT）定量分析的影响。给出了描述导致真符合或偶然符合的物理因素的基本表达式，以提供对比这两种现象的框架。结果表明，对湮灭辐射衰减或探测器效率不均匀性进行图像数据校正会放大数据中偶然符合的存在所导致的误差。研究表明，未能补偿偶然符合会导致从图像数据测量同位素浓度时出现高估，而且在许多情况下，对于数据中相对较小比例的偶然符合，高估程度也很显著。评估了三种偶然符合补偿方法的准确性及其对图像统计噪声的影响。结果发现，如果在从图像数据中确定和减去偶然符合时采用的方法不当，探测器效率不均匀可能会导致明显的图像伪影。从总符合数据中减去偶然符合在图像中产生的额外统计噪声表明，尽管有能力充分测量和补偿数据中偶然符合的存在，但尽量降低偶然符合率是明智的。
