Intra- and Interoperator Variations in Region-of-Interest Drawing and Their Effect on the Measurement of Glomerular Filtration Rates

PURPOSE:Quantitative results are often obtained from images after drawing regions of interest (ROIs) about the organ or area being evaluated. The accuracy and reproducibility of ROIs is an important aspect of quality-control protocols. Attempts to increase ROI accuracy and precision by generating them automatically must be compared with manually processed images to evaluate the success of the automatic methods. Operators' abilities to reproduce ROIs and the effect this has on the reproducibility of estimating glomerular filtration rate from renograms were assessed. METHODS:Estimation of the glomerular filtration rate using Sampson's method requires a) exclusion ROIs around both kidneys for background subtraction, b) whole-kidney ROIs, and c) exclusion ROIs for the collecting system. Two nuclear medicine professionals were asked to produce glomerular filtration rate estimates for 20 patients with diverse renal function. This was repeated 1 month later. The intra- and interoperator variations were calculated for the glomerular filtration rate results and on a pixel basis for the ROIs. RESULTS:The percentage of common pixels, on average, for a) intraoperator repeats and b) interoperator comparisons were a) 95%, 94%, 85%, and b) 94%, 93%, and 81% for region types 1, 2, and, 3, respectively. Analysis of variance for the glomerular filtration rate estimates showed significant variations in estimates for left kidneys (P < 0.025) but none (P > 0.1) for right kidneys. CONCLUSION:Spatial reproducibility in ROI drawing does not necessarily relate directly to the associated quantitative reproducibility.