Enhanced sonography of the urinary tract

Abstract

In the evaluation of the urinary tract, ultrasound contrast agents (USCAs) have been shown to be useful. USCAs do not have any renal toxicity. In the screening of renovascular hypertension, contrast-enhanced Doppler sonography improves the detection of main and supernumerary renal arteries, and reduces the frequency of technical failures. Using first-generation USCAs, the detection of renal cortical perfusion was achieved through the destruction of the bubbles to maximize the backscattered signals, requiring intermittent imaging to allow refilling of capillaries. Now, continuous non-destructive imaging has become possible with more recent agents using low and very low mechanical index values. The diagnosis of perfusion defects (i.e., renal infarct, pyelonephritis) is facilitated when the baseline Doppler signal is insufficient. USCAs improve detection of intratumoral blood flow and may be useful for characterization and/or detection of small, cystic, or nondetermined lesions at baseline US. As microbubbles remain strictly inside vessels, they can be viewed as blood pool markers, enabling functional imaging of the kidney. Bolus and infusion techniques are the two modalities of administration of the USCAs. Resulting time-intensity curves allow to approach renal blood flow and regional blood volume, and to provide additional information on perfusion disorders. Cystosonography has proven to be highly sensitive in the detection and grading of vesico-ureteral reflux in children.