Bailey D L, Jones T, Spinks T J
MRC Cyclotron Unit, Hammersmith Hospital, London, UK.
Eur J Nucl Med. 1991;18(6):374-9. doi: 10.1007/BF02258426.
A need exists to measure the absolute sensitivity of a positron emission tomographic (PET) scanner in units of counts.s-1.MBq-1. At present sensitivity is generally determined by measurement of a radionuclide of known concentration distributed in a water-filled cylindrical phantom, usually 20 cm in diameter. The measurement is confounded by self-attenuation of the source and scatter within the cylinder and does not give a true absolute sensitivity measurement. Due to variations in the magnitude and treatment of these factors, meaningful comparison between different manufacturer's scanners is difficult, as are comparisons between different acquisition geometries (e.g. with and without interplane septa present). A method has been developed in our laboratory that provides measurements of absolute sensitivity in air for a scanner independent of attenuation and scatter within the source. The method involves measurements of a thin-line source of fluorine 18 contained within an aluminium housing to which successive aluminium sleeves are added. The extrapolation of these measurements allows an effective counts.s-1.MBq-1 measurement to be made for zero thickness of aluminium. Measurements have yielded absolute sensitivities of 3926 +/- 61 counts.s-1.MBq-1 (0.39% efficiency), 5079 +/- 26 counts.s-1.MBq-1 (0.51%), and 32312 +/- 544 counts.s-1.MBq-1 (3.2%) for a whole-body PET scanner with interplane septa and for a NeuroPET operating with and without interplane septa, respectively.
需要以计数·秒⁻¹·兆贝克勒尔⁻¹为单位来测量正电子发射断层扫描仪（PET）的绝对灵敏度。目前，灵敏度通常是通过测量分布在充满水的圆柱形体模（通常直径为20厘米）中的已知浓度的放射性核素来确定的。该测量受到源的自衰减和圆柱体内散射的影响，无法给出真正的绝对灵敏度测量值。由于这些因素的大小和处理方式存在差异，不同制造商的扫描仪之间难以进行有意义的比较，不同采集几何结构（例如有无平面间隔板）之间的比较也很困难。我们实验室开发了一种方法，可在空气中测量扫描仪的绝对灵敏度，且不受源内衰减和散射的影响。该方法涉及测量包含在铝壳内的氟18细线源，并向其添加连续的铝套筒。通过对这些测量值进行外推，可以在铝厚度为零时进行有效的计数·秒⁻¹·兆贝克勒尔⁻¹测量。对于带有平面间隔板的全身PET扫描仪以及分别在有和没有平面间隔板情况下运行的神经PET，测量得到的绝对灵敏度分别为3926±61计数·秒⁻¹·兆贝克勒尔⁻¹（效率0.39%）、5079±26计数·秒⁻¹·兆贝克勒尔⁻¹（0.51%）和32312±544计数·秒⁻¹·兆贝克勒尔⁻¹（3.2%）。
