US units with a higher BNR are preferred because these provide greater uniformity of heat transmission across the sound head. PSWD offers a mode of heating that results in less intense heating effects...

US units with a higher BNR are preferred because these provide greater uniformity of heat transmission across the sound head.

PSWD offers a mode of heating that results in less intense heating effects than US; therefore it may be a more appropriate choice when treating acute or subacute conditions.