Redistribution of renal blood flow after SWL evaluated by Gd-DTPA-enhanced magnetic resonance imaging.

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.

Accurate determination of chemical composition of urinary calculi by spiral computerized tomography.

PURPOSE: Choice of efficacious clinical management of symptomatic renal calculi can be facilitated by ascertaining the precise chemical composition of the calculus. Spiral computerized tomography (CT) is becoming a frequently used radiographic examination to establish the diagnosis and severity of calculus disease. Our objective for this study was to determine the precision of spiral CT in identifying the chemical composition of 6 different types of urinary calculi with region of interest measurements using spiral CT. MATERIALS AND METHODS: A total of 102 chemically pure stones were separated into 6 groups. The stones along with phantoms containing butter (fat) and jello (water) were mounted vertically in the scanner gantry. Then 1 mm. thickness scanning was performed with a high speed scanner at the 2 energy levels of 80 and 120 kV. The determination of the chemical composition was performed using the absolute CT value measured at 120 kV. and the dual kilovolt CT values measured at 80 and 120 kV. Hounsfield unit at 80 kV.-Hounsfield unit at 120 kV.). RESULTS: The absolute CT value measured at 120 kV. was able to identify precisely the chemical composition of uric acid, struvite and calcium oxalate stones. It was imprecise in differentiating calcium oxalate from brushite stone and struvite from cystine stone. However, dual kilovolt CT value was able to differentiate these latter stones with statistical significance (p < 0.03). Uric acid stones were easily differentiated from all other stones using the absolute CT value. CONCLUSIONS: This study demonstrates that the chemical composition of urinary calculi can be accurately determined by CT scanning in an in vitro setting.