A physical therapist assistant reviews a patient coverage fo…

A physical therapist assistant reviews a patient coverage form that lists the parameters used during a recent ultrasound treatment to the right anterior shoulder: 1.0 W/cm2, continuous, 1 MHz, 6 minutes. The patient has recently reinjured the shoulder and the PT does not want a thermal effect. Which of the following parameters would be the MOST critical for the PTA to alter?