Detection of focal renal perfusion defects in rabbits after sulphur hexafluoride-filled microbubble injection at low transmission power ultrasound insonation

The aim of this study was to assess the feasibility of contrast-enhanced ultrasound (US) at low transmission power insonation for diagnosis of focal renal perfusion defects (RPDs) in rabbits. In seven adult New Zealand White rabbits focal RPDs were induced by polyvinyl alcohol embolizing particles (150-250 mu m in diameter) injected into the abdominal aorta. Three other rabbits that were not subjected to embolization were considered as controls. Both kidneys were insonated at baseline and after injection of sulphur hexafluoride-filled microbubbles at low transmission power (mechanical index 0.09-0.12). One sonologist assessed on-site RPD dimensions and conspicuity (visual score 0-4). Digital cine-clips were also reviewed off-site by two other independent readers, blinded, who assigned a confidence level (grades 1-5) for the RPD diagnosis. At on-site analysis RPDs appeared as focal areas of absent or diminished enhancement with a median visual conspicuity score=4. At off-site analysis RPDs > 6 mm in diameter were identified at contrast-enhanced US, and the confidence in RPD diagnosis improved significantly (P < 0.05) after microbubble injection (area under receiver operating characteristic curve 0.615 vs 0.972 by reader 1; 0.720 vs 0.953 by reader 2). Contrast-enhanced US at low transmission power insonation effectively identified RPDs with diameters > 6 mm in rabbits.