OPTIMIZING BACKGROUND CORRECTION WHEN CALCULATING DIFFERENTIAL RENAL-FUNCTION IN THE PRESENCE OF HYDROURETERONEPHROSIS USING TC-99(M)-DTPA

We performed a prospective study to establish the optimal background c orrection algorithm for the determination of differential renal functi on (DRF), using Tc-99(m)-diethylenetriamine pentaacetate (Tc-99(m)-DTP A) in the presence of unilateral hydronephrosis, with 24 h Tc-99(m)-di mercaptosuccinic acid (Tc-99(m)-DMSA) uptake as the `gold standard'. F rom September 1996 to June 1997, 12 males and 4 females (mean age 10 y ears, range 1 month to 72 years), presenting with unilateral hydroneph rosis, were studied. All patients underwent both DTPA renography and q uantitative DMSA scintigraphy within 24 h. In all patients, using a su rface method, the DRF of the obstructed kidney was determined using in frarenal, suprarenal and perirenal background correction, time interva ls of 60-180 s (t(1)), 120-180 s (t(2)) and 80-140 s (t(3)), and the a pplication or non-application of a Rutland-Patlak correction (RPC). In the absence of RPC, for all three types of background correction, no difference in DTPA DRF for any of the three time intervals was noted; higher DTPA DRF values were found (mean +/- S.D.: overestimates of 7.8 +/- 24.4%, 6.5 +/- 9.5% and 3.3 +/- 14.9% for suprarenal, infrarenal and perirenal background correction, respectively). Application of RPC resulted in an overall decrease in both the mean and standard deviati on values, which was most pronounced with infrarenal background correc tion: -0.38 +/- 6.5% for t 1, 0.31 +/- 6.3% for t(2) and -1.3 +/- 6.9% for t(3) (t(1) vs t(2) P = 0.06; t(3) vs t(1) or t(2), P = 0.04). Our results suggest that infrarenal background correction using t(1) or t (2) and RPC is the best algorithm for DRF estimation using Tc-99(m)-DT PA renography. ((C) 1998 Chapman & Hall Ltd.).