Borovnicar D J, Stroud D B, Wahlqvist M L, Strauss B J
Body Composition Laboratory, Monash Medical Centre, Clayton, Melbourne, Victoria, Australia.
Australas Phys Eng Sci Med. 1996 Dec;19(4):252-63.
The construction, calibration and evaluation of a prompt- gamma in vivo neutron activation analysis (IVNAA) facility for the simultaneous measurement of total body nitrogen (TBN) and chlorine (TBCl) in children is described. Subjects are irradiated unilaterally by a 0.2 GBq 252Cf neutron source from shoulder to mid thigh in both supine and prone positions. Prompt gamma-ray spectra are measured with two pairs of NaI(TI) crystals (each crystal: 10 cm x 10 cm x 15 cm) positioned on both sides of the subject. TBN and TBCl are estimated from the ratios of nitrogen-to-hydrogen (Nc/Hc) and chlorine-to-hydrogen (Clc/Hc) counts as determined from the measurement of 10.83 MeV, 8.57 MeV and 2.22 MeV prompt gamma-rays from the respective reactions 14N(n, gamma)15N, 36Cl(n, gamma)35Cl, and 1H(n, gamma)D. Nc/Hc and Clc/Hc are corrected for the effect of body width and thickness on background and gamma-ray attenuation. Total body hydrogen (TBH) is used as an internal standard which is independently determined using a four compartment model of body weight defined as the sum of total body water (TBW) measured by the D2O dilution technique, total body protein (TBPr) (i.e. 6.25 x TBN) measured by IVNAA, total body bone mineral (TBBM) measured by dual energy x-ray absorptiometry and total body fat (TBF) estimated as body weight less the sum of TBW, TBPr and TBBM. The effective dose equivalent to a small child is 0.25 mSv (Q = 20) per measurement scan. Repeated measurements of a child-size bottle phantom containing tissue-equivalent concentrations of nitrogen and chlorine yield respective intra- and inter-assay precision values of 2.8% (CV) and 2.3% for TBN measurements, and 7.9% and 10.0% for TBCl measurements. Similarly, intra- and inter-assay accuracy is determined to be respectively +0.1% +/- 1.0% (mean, 95% confidence interval) and +1.4% +/- 1.4% for TBN measurements, and +2.3% +/- 4.3% and +3.9% +/- 6.0% for TBCl measurements.
本文描述了一种用于同时测量儿童全身氮（TBN）和氯（TBCl）的瞬发γ体内中子活化分析（IVNAA）设备的构建、校准和评估。受试者在仰卧位和俯卧位时均由一个0.2 GBq的252Cf中子源从肩部到大腿中部进行单侧照射。用两对NaI（TI）晶体（每个晶体：10 cm×10 cm×15 cm）测量瞬发γ射线光谱，这两对晶体放置在受试者两侧。TBN和TBCl通过氮与氢（Nc/Hc）以及氯与氢（Clc/Hc）的计数比来估算，这些计数比是根据分别来自14N（n，γ）15N、36Cl（n，γ）35Cl和1H（n，γ）D反应的10.83 MeV、8.57 MeV和2.22 MeV瞬发γ射线的测量结果确定的。Nc/Hc和Clc/Hc针对身体宽度和厚度对本底及γ射线衰减的影响进行了校正。全身氢（TBH）用作内标，它是使用体重的四室模型独立确定的，该模型定义为通过D2O稀释技术测量的全身水（TBW）、通过IVNAA测量的全身蛋白质（TBPr）（即6.25×TBN）、通过双能X射线吸收法测量的全身骨矿物质（TBBM）以及估算为体重减去TBW、TBPr和TBBM总和的全身脂肪（TBF）之和。每次测量扫描对一个含有组织等效浓度氮和氯的儿童尺寸瓶体模的重复测量，TBN测量的批内和批间精密度值分别为2.8%（CV）和2.3%；TBCl测量的批内和批间精密度值分别为7.9%和10.0%。同样，TBN测量的批内和批间准确度分别确定为+0.1%±1.0%（平均值，95%置信区间）和+1.4%±1.4%；TBCl测量的批内和批间准确度分别为+2.3%±4.3%和+3.9%±6.0%。
