Abstract: Apparatus and methods for treating in-stent restenosis are described for removing stenotic material from within previously stented regions of a patient's vasculature. The apparatus includes a catheter system having a stenotic material removal mechanism mounted on a distal portion of an elongated inner catheter. A sensing means, such as one or more sensing electrodes, are positioned on an outer surface of the apparatus. In addition, the apparatus optionally includes control means for diametrically expanding the stenotic material removal mechanism for effective recanalization of the stent. A coaxial outer catheter is provided for aspirating stenotic material which is removed from within the stent. In addition, embolic filter apparatus are described for collecting the stenotic material removed from within the stent.