Frequency dependence of kidney injury induced by contrast-aided diagnostic ultrasound in rats.

This study was performed to examine the frequency dependence of glomerular capillary hemorrhage (GCH) induced by contrast-aided diagnostic ultrasound (DUS) in rats. Diagnostic ultrasound scanners were used for exposure at 3.2, 5.0 and 7.4 MHz, and previously published data at 1.5 and 2.5 MHz was also included. A laboratory exposure system was used to simulate DUS exposure at 1.0, 1.5, 2.25, 3.5, 5.0 and 7.5 MHz, with higher peak rarefactional pressure amplitudes (PRPAs) than were available from our DUS systems. The right kidneys of rats mounted in a water bath were exposed to intermittent image pulse sequences at 1 s intervals during infusion of diluted ultrasound contrast agent. The percentage of GCH was zero for low PRPAs, and then rapidly increased with increasing PRPAs above an apparent threshold, p(t). The values of p(t) were approximately proportional to the ultrasound frequency, f, such that p(t) /f was approximately 0.5 MPa/MHz for DUS and 0.6 MPa/MHz for laboratory system exposures. The increasing thresholds with increasing frequency limited the GCH effect for contrast-aided DUS, and no GCH was seen for DUS at 5.0 or 7.4 MHz for the highest available PRPAs.