An ultrasound catheter comprising: an elongate flexible catheter body having a proximal end, a distal end and at least one lumen extending longitudinally therethrough, an ultrasound transmission member extending longitudinally through the lumen of the catheter body, the ultrasound transmission member having a proximal end and a distal end positioned at the distal end of the catheter body, a sonic connector positioned at the proximal end of the ultrasound transmission member for connecting the ultrasound transmission member to a separate ultrasound generating device, the sonic connector comprising a proximal section for connection to the separate ultrasound generating device and a front portion extending distally from a central portion of the sonic connector, the sonic connector having a bore which receives the proximal end of the ultrasound transmission member, the catheter further comprising a knob housing which houses at least the front portion of the sonic connector inside a bore of the knob housing, with the ultrasound transmission member extending through that bore, the bore comprising a narrowed portion where the bore diameter is reduced through which the ultrasound transmission member extends, wherein the narrowed portion is provided at an intermediate position between the frontmost part of the sonic connector and the point where the ultrasound transmission member exits the knob housing, further comprising absorbing means (330e, 330f) retained inside the bore so as to surround the ultrasound transmission member, the absorbing means (330e, 330f) being provided both proximally and distally of the narrowed portion, the absorbing means proximally and distally of the narrowed portion being positioned so as to contact those parts of the knob housing which form the narrowed portion. an elongate flexible catheter body having a proximal end, a distal end and at least one lumen extending longitudinally therethrough, an ultrasound transmission member extending longitudinally through the lumen of the catheter body, the ultrasound transmission member having a proximal end and a distal end positioned at the distal end of the catheter body, a sonic connector positioned at the proximal end of the ultrasound transmission member for connecting the ultrasound transmission member to a separate ultrasound generating device, the sonic connector comprising a proximal section for connection to the separate ultrasound generating device and a front portion extending distally from a central portion of the sonic connector, the sonic connector having a bore which receives the proximal end of the ultrasound transmission member, the catheter further comprising a knob housing which houses at least the front portion of the sonic connector inside a bore of the knob housing, with the ultrasound transmission member extending through that bore, the bore comprising a narrowed portion where the bore diameter is reduced through which the ultrasound transmission member extends, wherein the narrowed portion is provided at an intermediate position between the frontmost part of the sonic connector and the point where the ultrasound transmission member exits the knob housing, further comprising absorbing means (330e, 330f) retained inside the bore so as to surround the ultrasound transmission member, the absorbing means (330e, 330f) being provided both proximally and distally of the narrowed portion, the absorbing means proximally and distally of the narrowed portion being positioned so as to contact those parts of the knob housing which form the narrowed portion.