A choke valve assembly is disclosed for controlling the flow of fluid through a production tubing. Methods of the invention can improve delivery of the therapeutic agent into the tissue, which can be beneficial for the treatment of a pelvic tissue disorder, such as bladder and prostate tumors. Also, when \u0394NT is greater than a preset value \u03b2, it is determined that a failure related to slipping of a frictional engaging element has occurred. The body has a V-shape supporting surface, wherein the V-shape supporting surface is along the axis direction of the shaft and supports on outer edge of the shaft. The element is secured to the inner sleeve with the aid of a fastening collar that is fastened around the inner sleeve. The body has a substantially transparent portion extending an axial length over which axially translatable imaging may be performed.