Evaluation of renal microcirculation by contrast-enhanced ultrasound with Sonazoid as a contrast agent

Chronic kidney disease (CKD) is a major and serious risk factor for cardiovascular disease (CVD). Continuous hypoxia due to hypoperfusion in peritubular capillaries is one of the factors aggravating CKD, but evaluation of perfusion in this region is difficult using clinically available imaging methods. Since the second-generation ultrasound contrast agent Sonazoid has a stable shell, it enables visualization of the renal vasculature for a long period of time. We therefore evaluated changes in contrast-enhanced ultrasound (CEUS) imaging with Sonazoid in CKD patients.Sonazoid was used in 85 CKD patients and 5 control subjects, and images were recorded for 10 minutes. Time-intensity curves were generated from the images of 62 time points in both cortex and medulla.In control samples, contrast enhancement spread from the hilar portion to the periphery along the direction of arterial flow, and renal cortex and medulla were then enhanced in sequence. Enhancement was maximal soon after, then gradually decreased, but was still visible at 600 seconds. In CKD patients, renal contrast enhancement was attenuated in both cortex and medulla. On time-intensity curves, the attenuation of enhancement was composed of delayed rising, reduction of peak, and acceleration of decay in both cortex and medulla with progression of renal dysfunction. No side effects of the contrast agent were observed in any subjects.The attenuation of renal contrast enhancement observed in CKD patients appears to reflect disturbance of perfusion in peritubular capillaries. CEUS with Sonazoid is a useful and safe means of visualizing the renal microvasculature.