An ultrasound system has an ultrasound transducer having a transducer housing and a horn provided at the distal end of the transducer housing, an ultrasound transmission member, a sonic connector that is connected to the horn and the proximal end of the ultrasound transmission member, and a catheter knob having a proximal end that is coupled to the distal end of the transducer housing. The catheter knob has a proximal bore that houses the sonic connector. The system also includes a nesting piece that is retained inside the proximal bore of the catheter knob. The nesting piece can be moved from a first position where the sonic connector is received inside the nesting piece to a second position where the sonic connector is separated from the nesting piece when ultrasound energy is being propagated through the ultrasound transmission member.