Therapeutic ultrasound and the liver in vivo: action and possible mechanisms.

This paper reports on the effects of therapeutic ultrasound upon the liver in vivo. Exposure of the liver of rats to therapeutic ultrasound at a frequency of 0.87 MHz results in intravascular haemolysis which is dependent upon the product of the intensity and the exposure duration (energy deposited within the liver). The resulting structural change (noted when a spatial peak intensity of 1.25 W/cm2 was applied for a duration of 10 min) is a lesion which has four zones. The severity of the injury increased across the four zones when scanning towards the ischaemic area. The biochemical changes observed included an increase in aspartate transaminase, alanine transferase, creatinine kinase and cholesterol and a decrease in total protein and albumin. Healing processes reversed the structural changes after 72 h which was also reflected in the plasma biochemical profile. Exposure of the liver to infrared radiation resulted in haemolysis but not the biochemical or structural alterations observed following sonication suggesting a mechanism for ultrasound action other than heating alone.