Evaluation of renal function in normal and hydronephrotic kidneys in rats using gadolinium diethylenetetramine-pentaacetic acid enhanced dynamic magnetic resonance imaging

Purpose: Magnetic resonance imaging (MRI) is becoming established as a moda lity complementary to computerized tomography and ultrasound for evaluating kidney function. The evaluation of renal function during ureteral obstruct ion may be improved by contrast enhanced MRI. We evaluated dynamic changes in relative signal intensity in normal and hydronephrotic rat kidneys after intravenous injection of gadolinium (Gd) diethylenetetramine-pentaacetic a cid (DTPA). Materials and Methods: Using Gd-DTPA enhanced dynamic MRI we evaluated 35, 1-year-old rats, including 10 with partial and complete unilateral ureteral obstruction, respectively, and 15 with sham operated nonobstructed kidneys . Partial obstruction was created in 2-day-old rats by embedding the left u reter into the psoas muscle. Complete obstruction was created 10 days befor e MRI by placing a ligature around the upper third of the left meter. MRI w as performed before and 0.1 to 60 minutes after and intravenous injection o f Gd-DTPA. We calculated relative signal intensity per time interval in the renal cortex, medulla and pelvis. Results: Dynamic relative signal intensity patterns differed significantly among normal, and partially and completely obstructed kidneys. In normal ki dneys signal intensity changes were divided into 3 phases after Gd-DTPA adm inistration. During phase 1 rapid parenchymal uptake of Gd-DTPA within the initial minute after injection produced a rapid signal intensity decrease i n the cortex, which achieved a minimum of 28% of pre-injection intensity. D uring phase 2 signal. intensity decreased in the medulla and pelvis to a mi nimum of 18% and 22%, respectively, of pre-injection intensity within 5 min utes. During phase 3 significant relative signal intensity recovery began i n the cortex at 7 minutes, and in the medulla and pelvis at 10 to 15 minute s, and lasted 30 to 60 minutes. In partially obstructed kidneys the 3 phase s were significantly slower than in controls. In completely obstructed kidn eys only phase 1 occurred within 60 minutes. Conclusions: Gd-DTPA enhanced dynamic MRI provides useful information for d istinguishing obstructed from nonobstructed and partially from completely o bstructed kidneys.