Dosage factors for the subaqueous application of 1MHz ultrasound

To determine and validate correction factors necessary to ensure consistent dosage of 1MHz ultrasound when applied in water at different applicator-to-skin distances and different levels of intensity.

An intervention study with a crossover design.

A laboratory.

Cross-sections of nonliving pig tissue.

Specimens were each exposed to 1MHz ultrasound under four subaqueous conditions: in contact with the skin and at 1, 2, and 4 centimeters from the applicator to the skin. These conditions were repeated for each of three intensity levels: 0.5W/cm2, 1.0 W/cm2, and 2.0 W/cm2.

Tissue temperatures were measured at six thermocouple locations at different depths from the skin surface.

Increasing the distance from the applicator to the skin from 0 to 1, 2, and 4 centimeters resulted in progressive and significantly lower mean maximum temperature increases. The same relation of distance to temperature increase was identified at all intensity levels and was used to calculate dosage factors for distance in water. By multiplying the required intensity by the calculated dosage factors, the temperature increases in tissue were found to equal those produced at 0 centimeters distance.

Large corrections to the intensity output are required to compensate when using ultrasound in water at different applicator-to-skin distances. These dosage (correction) factors are reliable for the range of intensity levels tested under the conditions examined.