Transmission electron microscopy study on the effects of the ultrasound contrast agent Levovist on hepatic cells

The Ultrasound Equipment and Safety Committee of The Japan Society of Ultrasonics in Medicine performed experiments to confirm whether contrast-enhanced ultrasonography damages liver cells.

Rats were injected with 0.1 ml of 300 mg/ml ultrasound contrast agent (UCA). Diagnostic ultrasound pulses with a center frequency of 6 MHz and a mechanical index of 1.9 were applied to rat livers with a water bag as a coupler to maintain a distance of 2-6 cm between the ultrasound probe surface and the liver. Contrast-enhanced ultrasonography was carried out for 10 s to visualize the entire liver. Then, specimens of liver tissue were fixed using two types of fixation: immersion and perfusion fixation.

Although some variations were found in electron micrographs of liver tissue fixed using immersion fixation, none of three blinded readers found any significant differences between micrographs of liver tissue from rats receiving UCA with sonication and those from sham-treated control rats. Changes observed were not thought to be group-specific but instead due to differences between individual rats. When the livers were fixed using perfusion fixation and the hepatic vein was cut after injection of physiological saline for perfusion, a large number of vacuoles ≥2 μm in diameter were observed. This finding suggested that hepatic cell damage observed in this study was caused by high perfusion pressure during the liver fixation process rather than by sonication with UCA.

Blinded readings of electron micrographs showed no clear evidence that the use of Levovist in ADI mode ultrasonography causes significant damage to liver tissue.