Differential renal function estimation by dynamic renal scintigraphy: influence of background definition and radiopharmaceutical

Differential renal function (DRF) calculation with Tc-diethylenetriamine-pentaacetic acid (DTPA) or mercaptoacetyltriglycine (MAG₃) is gaining clinical importance in the evaluation of patients with ureteropelvic junction obstruction with hydronephrosis (HN). Although many decisions regarding surgery are based on the functional changes detected by serial diuretic renography, the reliability of DRF estimation has been questioned. Factors such as the correction of nonrenal activity included in the renal region of interest (background subtraction) and immature function resulting in poor renal extraction may cause unusual elevation in the differential function. The aim of this study is to evaluate the impact of the radiopharmaceutical and positioning of the background on the DRF. A prospective study was undertaken in 83 patients (48 male, 35 female, median age 5 years) with unilateral or bilateral ureteropelvic junction obstruction with or without HN. Forty-five and 38 renograms were performed with ^99mTc-DTPA and ^99mTc-MAG₃, respectively. DRF was calculated using two different regions of interest (subrenal and perirenal) for background subtraction. Of the 83 patients, 37 also had dimercaptosuccinic acid scans. The difference between DRF based on background selection, age, radiopharmaceutical, and correlation with dimercaptosuccinic acid uptake was analyzed. The difference in DRF between two background (BG) drawings (sebrenal and perirenal) and 95% confidence intervals were calculated.