Redistribution of Renal Blood Flow after SWL Evaluated by Gd-DTPA-Enhanced Magnetic Resonance Imaging

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Abstract
Extracorporeal shockwave lithotripsy (SWL) is currently accepted as an effective noninvasive treatment for a wide variety of urinary tract calculi. However, the bioeffects of high-energy shockwaves on renal parenchyma have yet to be fully elucidated. The objective of this study was to measure the acute changes in regional renal hemodynamics associated with SWL utilizing dynamic gadolinium-DTPA-enhanced magnetic resonance imaging (MRI). Seven patients who underwent SWL for renal calculi had an MRI study within 4 hours after the treatment. To assess renal hemodynamics, a bolus of Gd DTPA (0.03 mmol/kg) was administered, and dynamic contrast enhanced images was obtained. Regions of interest (ROI) were defined over the cortex and medulla to obtain signal intensity-v-time curves. The contralateral kidney in each patient was used as the control. The initial slope of the contrast-enhanced signal intensity-v-time curve was used as a measure of the perfusion index (PI). In six patients, perfusion imaging showed a consistent trend of decreased cortical flow (29 ± 8%) and a concomitant increase in medullary flow (34 ± 14%) in the region of the kidney that was targeted with SWL in six patients (86%). This study shows that renal hemodynamics are modified by SWL. We hypothesize that this change represents a shunting of flow from cortex to medulla in an attempt to prevent ischemia of the medulla.