Abstract: A balloon dilatation catheter is disclosed which incorporates an elongate shaft which is at least partially optically transparent. The shaft includes an inflation lumen and a guide wire lumen extending therethrough in addition to an inflatable balloon connected to its distal end. The inflatable balloon may include a measuring index disposed thereon. The measuring index may comprise a plurality of longitudinally-spaced radial bands, a plurality of radially-spaced longitudinal bands, or a combination thereof. A method of using an angioscope in combination with a balloon catheter is also disclosed. The method involves inserting a balloon catheter with an optically transparent shaft section into a vascular lumen, inserting an angioscope into the balloon catheter, inflating the balloon on the balloon catheter, and measuring material characteristics of abnormal deposits therein.