Surma Marian J
Nuclear Medicine Department, Medical University of Łódź, Poland.
Nucl Med Rev Cent East Eur. 2009;12(1):14-22.
The aim of the present study was the assessment of the accuracy and precision of our own simplified method for the determination of (99m)Tc-HEPIDA liver clearance.
It has been assumed that archived results of plasma clearance (Cl(Pl)) and hepatic (Cl(Hp)), determined by means of multisample methods, could be legitimately used as a reference standard. The accuracy and precision of the simplified method was assessed by means of a Monte Carlo method alternatively utilizing three blood sampling times (T) of 68, 75 and 83 minutes post i.v. administration of (99m)Tc-HEPIDA. The corresponding alternative three urine voiding times (Y) were: 75, 80, and 95 min p.i. The analysed model was created accepting values of Cl(Pl) and Cl(Hp), of administered activity A(p) and parameters of biexponential function, describing the concentration C(t) decrease of the radiopharmaceutical (RF) in plasma during time as real values. Using the function C(t) for each individual, the plasma concentrations of RF at three sampling times, urinary clearance (Cl(Pl) - Cl(Hp)), and voided activity (A(Ur)(Y)) were calculated. Simulated random errors were added to the assumed blood sampling times T and to voiding time Y. To the activity A(p) and A(Ur)(Y), and RF plasma concentrations random errors were added, assuming normal distribution with relative SD from 0 to 5% and then clearance values were computed. For each process there were 5000 repeated simulated determinations. The accuracy of the simplified methods was assessed by comparing mean values of simulated clearance computations with the reference. Comparison of standard deviations with mean uncertainties enabled us to gain insight into the degree of agreement of the estimator of relative uncertainty with the coefficient of variation as a measure of precision.
There were strong correlations between the reference clearance values and the mean values of determinations by means of the simplified procedure (r > 0.93). The correlations were practically insensitive to the uncertainty of pipetting. The lines of regression differed slightly from the lines of identity, giving an indication that there was a systematic error involved; it amounted to +4 ml/min at Cl(Pl) = 60 ml/min and to -7 ml/min for Cl(Pl) of 370 ml/min. For Cl(Pl) a bias of +6 ml/min was found for a clearance value of 16 ml/min and -13 ml/min at Cl(Pl) > 300 ml/min. At uncertainty of pipetting of 2%, a precision of 6-7% was found for Cl(Pl) of 300 ml/min. For Cl(Pl) of 200 and 150 ml/min the corresponding precisions were 7-8% and 10%, respectively. For Cl(Pl) of 200, 150 and 100 ml/min the corresponding precisions were 10, 12 and 17%, respectively. These precisions are 5 percent worse than those that were obtained from determinations by means of multisampling procedures.
本研究的目的是评估我们自己简化的测定（99m）Tc-HEPIDA肝脏清除率方法的准确性和精密度。
假设通过多样本方法测定的血浆清除率（Cl(Pl)）和肝脏清除率（Cl(Hp)）的存档结果可合理用作参考标准。通过蒙特卡罗方法评估简化方法的准确性和精密度，该方法交替使用静脉注射（99m）Tc-HEPIDA后68、75和83分钟的三个采血时间（T）。相应的三个排尿时间（Y）分别为：给药后75、80和95分钟。所分析的模型通过接受Cl(Pl)和Cl(Hp)的值、给药活度A(p)以及双指数函数的参数来创建，该双指数函数将放射性药物（RF）在血浆中随时间的浓度C(t)降低描述为实际值。对于每个个体，使用函数C(t)计算三个采样时间的RF血浆浓度、尿清除率（Cl(Pl) - Cl(Hp)）和排尿活度（A(Ur)(Y)）。将模拟随机误差添加到假定的采血时间T和排尿时间Y。向活度A(p)和A(Ur)(Y)以及RF血浆浓度添加随机误差，假设其呈正态分布，相对标准差从0到5%，然后计算清除率值。对于每个过程进行5000次重复模拟测定。通过将模拟清除率计算的平均值与参考值进行比较来评估简化方法的准确性。将标准差与平均不确定度进行比较，使我们能够深入了解相对不确定度估计值与作为精密度度量的变异系数的一致程度。
参考清除率值与简化程序测定的平均值之间存在强相关性（r > 0.93）。这些相关性对移液的不确定性实际上不敏感。回归线与恒等线略有不同，表明存在系统误差；当Cl(Pl) = 60 ml/min时，系统误差为 +4 ml/min，当Cl(Pl)为370 ml/min时为 -7 ml/min。对于Cl(Pl)，当清除率值为16 ml/min时偏差为 +6 ml/min，当Cl(Pl) > 300 ml/min时为 -13 ml/min。在移液不确定度为2%时，发现Cl(Pl)为300 ml/min时的精密度为6 - 7%。对于Cl(Pl)为200和150 ml/min，相应的精密度分别为7 - 8%和10%。对于Cl(Pl)为200、150和100 ml/min，相应的精密度分别为10%、12%和17%。这些精密度比通过多样本程序测定获得的精密度差5%。
