DIURETIC RENOGRAM:COMPARISON OF QUANTITATIVE PARAMETERS FOR EVALUATION OF RENAL DRAINAGE IN OBSTRUCTIVE UROPATHY

Introduction: The purpose of this study was to evaluate the diagnostic ability of Normalized Residual Activity (NORA) in detecting urinary tract obstruction compared to the conventional interpretation of renogram (CIR) using a standard F0 diuretic protocol with 99mTc-EC renography in both children and adults.

Methods: After institutional ethical board approval and written informed consent, 90 patients with hydronephrotic kidney / suspected urinary tract obstruction referred for diuretic renography were enrolled in this study. Diuretic renography was performed using 99mTc-EC with F0 diuretic protocol according to standard guidelines and image processing and reconstruction was done on Xeleris-3 workstation. The kidneys were divided into three groups i.e., normal, unobstructed hydronephrotic and obstructed, based on the renogram curves, diuretic T1/2 and pre-void and post-void images and mean values of NORA20 and NORA50 for each group were calculated. These NORA values were compared between obstructed and unobstructed groups and also between normal and unobstructed hydronephrotic groups and a cut off value for NORA to diagnose obstructed drainage was derived.

Results: Both NORA20 and NORA50 values showed statistically significant difference between obstructed and unobstructed hydronephrotic kidneys. Mean NORA50 between normal kidneys and unobstructed hydronephrotic kidneys was not showing statistically significant difference, where as it was significantly different for NORA20. NORA50 cutoff value to differentiate obstructed kidneys from unobstructed hydronephrotic kidneys was 0.37.

Conclusions: Our study showed that NORA50 is a reliable parameter to differentiate obstructed kidneys from unobstructed hydronephrotic kidneys due to the effect of gravity assisted drainage, in contrast to NORA20, which can show abnormally high values in grossly hydronephrotic unobstructed kidneys. Kidney showing equivocal renogram curve can be diagnosed as having obstructed drainage if the NORA50 value is greater than 0.37.