An apparatus for performing an endovascular procedure using ultrasonic energy includes a catheter with a proximal end portion and a distal end portion. The distal end portion includes a first window, which may expose a wave guide for delivering the ultrasonic energy for performing the endovascular procedure. A cover may be provided for selectively covering the window. By selectively controlling the position of the sheath, the transmission of ultrasonic energy may be regulated accordingly for providing a desired treatment regimen.