Defrise M, Townsend D W, Bailey D, Geissbuhler A, Michel C, Jones T
Division of Nuclear Medicine, AZ-VUB, Brussels, Belgium.
Phys Med Biol. 1991 Jul;36(7):939-52. doi: 10.1088/0031-9155/36/7/003.
Prior to reconstruction, emission data from a multi-ring PET camera must be corrected (normalized) for variations in detector sensitivity. The appropriate correction coefficients are obtained by measuring the response of all coincidence lines to a calibrated source of activity (a blank scan). State-of-the-art cameras may contain up to a million such lines of response (LORs), and therefore around 400 million counts will be required to calibrate each LOR to a statistical accuracy of 5%. Alternatively, by modelling the LOR sensitivity as the product of the individual detector efficiencies and a geometrical factor, a calibration procedure has been proposed which requires the determination of only 6000 parameters from this same data set. A significant improvement in the statistical accuracy of the coefficients can therefore be expected. Recently, multi-ring scanners have been operated with the septa retracted, increasing the number of measured LORs by a factor of eight. The acquisition of the calibration data necessary to achieve adequate statistical accuracy then becomes prohibitive. We show that, by modelling the LOR sensitivity, it is possible, with certain approximations, to normalize a septa-retracted emission data set with good accuracy. The input to the model is a high statistics blank scan acquired with the septa extended, which offers a number of practical advantages.
在重建之前，多环正电子发射断层扫描（PET）相机的发射数据必须针对探测器灵敏度的变化进行校正（归一化）。通过测量所有符合线对校准后的活度源（空白扫描）的响应来获得适当的校正系数。最先进的相机可能包含多达一百万个这样的响应线（LOR），因此需要约4亿个计数才能将每个LOR校准到5%的统计精度。或者，通过将LOR灵敏度建模为各个探测器效率与几何因子的乘积，已经提出了一种校准程序，该校准程序仅需要从同一数据集中确定6000个参数。因此，可以预期系数的统计精度会有显著提高。最近，多环扫描仪在隔板缩回的情况下运行，使测量的LOR数量增加了八倍。那么获取达到足够统计精度所需的校准数据就变得令人望而却步。我们表明，通过对LOR灵敏度进行建模，在某些近似情况下，可以以良好的精度对隔板缩回的发射数据集进行归一化。该模型的输入是在隔板伸出时采集的高统计量空白扫描，这具有许多实际优势。
