Noncontrast and contrast enhanced MR imaging in the evaluation of partial ureteral obstruction: an experimental study in the micropig.

Twelve Yucatan micropigs (3 controls; 3 sham-operated; 6 with unilateral obstruction) were studied to assess the value of noncontrast and contrast-enhanced (Gadolinium-DTPA) magnetic resonance (MR) imaging in the evaluation of partial ureteral obstruction. MR findings were correlated with findings of quantitative (Tc-99m-DMSA) scintigraphy, and histology. On noncontrast T1-weighted images, the normal porcine kidney demonstrated good corticomedullary contrast (CMC = 16.8% +/- 5.0). Five minutes after administration of Gd-DTPA, there was enhancement of the renal cortex (+24.4% and medulla (+46.2%), and CMC was no longer discernible. Enhancement of the urine within the collecting system (+119.1%) was also observed. The obstructed kidneys demonstrated marked thinning of the renal parenchyma and decreased signal intensity on noncontrast T1- and T2-weighted images (P less than 0.01). Urine in the dilated collecting system did not differ significantly from urine in controls except in the three animals with urinary tract infection (P less than 0.05). Five minutes following injection of Gd-DTPA, there was enhancement of the renal parenchyma in all kidneys. Excretion was seen in three pigs and no excretion in two. Thus, useful information can be obtained in partial ureteral obstruction from both pre-contrast and Gd-DTPA-enhanced MR images of the kidney.