Evaluation of free radical formation associated with diagnostic ultrasound

Our objective was to evaluate kidney antioxidant status in rats subjected to an ultrasound examination. Thirty rats were divided into five groups for injection of saline (S) or anesthetic (A), and application of ultrasound using different modes, B mode, pulsed wave Doppler, and continuous wave Doppler, under anesthesia. Ultrasound was performed on days 1, 3, and 5 relative to the initiation of the experiment. Rats were then scarified on day 6. The kidney tissue thiobarbituric acid reactive substance (TBARS) level and superoxide dismutase (SOD) activity were measured. Both TBARS level and SOD activity increased, 21% and 38%, respectively, due to anesthesia (P < 0.04 for both). SOD activity increased further by a factor of 1.2 in response to ultrasound examination (P < 0.05), whereas TBARS level was not affected by Doppler and continuous wave Doppler compared to anesthesia. Increases in the level of TBARS (P < 0.03) and SOD activity (P < 0.01) were greatest when B-mode ultrasound was employed. These substances did not increase further when continuous wave Doppler was employed. The peak-negative acoustic pressure (9.16 vs. 9.74 MPa) and frequency (3.57 vs. 6.95 MHz) for B mode and pulsed wave Doppler were greater than those for continuous wave Doppler (0.22 MPa and 1.96 MHz). The estimated mechanical indexes were 4.87, 3.70, and 0.15 for B mode, pulsed wave Doppler, and continuous wave Doppler, respectively. In conclusion, anesthesia may cause tissue damage as reflected by elevated lipid peroxidation and free radical formation and ultrasound examination may amplify tissue damage through mechanical effects caused by ultrasound absorption.