Quantitative evaluation of renal excretion on the dynamic DTPA renal scan

In order to evaluate the renal excretion quantitatively, the authors analyzed the Tc-99m DTPA renogram using mean transit time (MTT) with deconvolution analysis and compared it to the perfusion index. One hundred thirteen studies consisting of 25 normal, 11 obstruction, 35 transplant-norm, 12 transplant-obstruction, and 30 transplant-rejection were evaluated. In the non-transplant obstruction, MTT is significantly long (3.40 +/- 0.85 minutes vs 2.02 +/- 0.42 minutes) and has high sensitivity (100%) and specificity (93%, 23/25) for the diagnosis of obstruction. In the transplant-obstruction, if the field of view includes both transplant and liver or spleen as a blood pool image, MTT has high sensitivity for the diagnosis (10/11) and for the follow up of obstruction (12/12), with the same specificity, but low sensitivity for rejection (25%). Perfusion index is of value in the diagnosis of rejection (73% specificity, 77% sensitivity) but is useless for the detection of obstruction (25% specificity, 75% sensitivity). The authors conclude that MTT is a useful marker for diagnosis and serial quantitative evaluation of renal obstruction. Also, they suggest the use of multiple techniques based on different principles for the complete evaluation of the renal scan.