Spinks T J
Phys Med Biol. 1979 Sep;24(5):976-87. doi: 10.1088/0031-9155/24/5/010.
The effect of size and composition of the body on the measurement of total calcium in absolute units by neutron activation analysis is described. The neutron beam, produced from a cyclotron, was of mean energy 7.5 MeV. Counting of the activities induced in a patient was carried out with a multidetector whole body counter. Calibration of the system was achieved by using two phantoms of different sizes containing known quantities of calcium. The dimensions of various phantom sections were varied to determine the effect on efficiency of activation, an approximately linear relationship with body thickness being found. The influence of body habitus on counting efficiency was assessed by counting different patients who had been given known quantities of 42K. The effects of (a) the non-uniform distribution of calcium and (b) the variation in density of different tissues on both activation and counting efficiency are discussed. It is estimated that the 68% confidence limits on the measurement of 49Ca count rate per unit neutron fluence is +/- 3.0% and on the measurement of calcium in grams +/- 8.2%.
描述了身体大小和组成对通过中子活化分析以绝对单位测量总钙的影响。由回旋加速器产生的中子束平均能量为7.5兆电子伏。使用多探测器全身计数器对患者体内诱发的放射性进行计数。通过使用两个含有已知量钙的不同尺寸的体模来实现系统校准。改变各种体模截面的尺寸以确定对活化效率的影响，发现与身体厚度大致呈线性关系。通过对给予已知量42K的不同患者进行计数来评估身体体型对计数效率的影响。讨论了（a）钙的不均匀分布和（b）不同组织密度变化对活化和计数效率的影响。据估计，每单位中子注量的49Ca计数率测量的68%置信限为±3.0%，钙克数测量的置信限为±8.2%。
