PT  - JOURNAL ARTICLE
AU  - Wesolowski, Carl
AU  - Puetter, Richard
AU  - Babyn, Paul
TI  - The inappropriateness of the sum of exponential terms for modelling plasma concentrations of bolus-injected, radiolabeled DTPA
DP  - 2010 May 01
TA  - Journal of Nuclear Medicine
PG  - 429--429
VI  - 51
IP  - supplement 2
4099  - http://jnm.snmjournals.org/content/51/supplement_2/429.short
4100  - http://jnm.snmjournals.org/content/51/supplement_2/429.full
SO  - J Nucl Med2010 May 01; 51
AB  - 429 Objectives Four statistical tests were applied to explore the problems in estimating plasma clearance (G ml/min) using Sums of (n) Exponential Terms (En SETs) fit to marker concentration of bolus-dilution of 169Yb-DTPA (n=41, 8 samples, 10-240 min) and 99mTc-DTPA (n=5, 9 samples, 5-180 min). Methods Test 1 characterized E2 SET’s parameter estimation error using bootstrap. Test 2 explored sample-subset selection effects on E1 and E2 SET parameters. Test 3 explored E2 SET goodness-of-fit testing. Test 4 examined E2 SET extrapolative errors. Results Test 1 found that 19/46 E2 elimination rate constants’ confidence intervals included 0, implying that the complexity of En>1 models was statistically unjustified. In Test 2, the standard deviation of residuals changed with sample-subset selection and was >3%, the maximum expected relative measurement error. Further, 8.1% of E2 fit attempts yielded degenerate E2 fits. Test 3 found the magnitude of the E2 models’ mean residuals failed t-testing for 6 of the 8 sample times. For all samples, Chi-squared testing of fit quality suggested poor fits (P<0.039, n=46). Test 4, extrapolation, showed significant underestimation of concentration over time (31/46 times, Wilcoxon signed-rank sum P=0.0035) and overestimation of G. Conclusions Consequently, SETs for modeling DTPA concentration are inappropriate and need replacement by better models