Histological analysis of healthy epithelium of Wistar rats in vivo irradiated with different intensities of therapeutic ultrasound.

Background: Ultrasound (US) is a widely used and studied resource for physical therapy treatments. Given the scarcity of studies on the effects of US on healthy tissue, many physical therapy professionals make unfounded decisions regarding its methods and parameters of application.

Objectives: The possible histological and morphometric changes in the healthy tissue of Wistar rats in vivo irradiated with different intensities of US were evaluated.

Methods: Thirty Wistar rats, randomly distributed among five groups of six animals each, were treated on the right side of the dorsal region, over an area of 4 cm(2). The left side served as a control. The treatment was applied over a four-day period, with two mins. of daily irradiation. The output intensity was checked using a precision dosimeter before the applications. Histological and morphometric analyses were performed using the Image Tool software.

Results: There were slight inflammatory infiltration and thinning of the dermis fibers, particularly in the groups irradiated with 1.5 and 2 W/cm(2). There was also thickening of the epidermis in the samples from the irradiated animals. To evaluate the quantitative results, the statistical analyses consisted of one-way ANOVAs with the post-hoc Tukey tests. There were significant differences in epidermis thicknesses between the control group and the groups irradiated with 1.0, 1.5 and 2.0 W/cm(2).

Conclusions: Higher doses of US produced changes in the epidermis and dermis, i.e. increased thickness and collagen fiber thinning and proliferation, respectively. These results serve as a warning of the possible implications of therapeutic ultrasound use in esthetics.