A flexible hollow shaft (2) is accommodated inside a catheter shaft (1) provided at its front end with a combination of a plaque removing rotating device (3) and an intravascular ultrasound sensor (4). A guiding wire (7) is inserted into the vessel before the combination is moved in, both operations watched on a monitor. The intravascular sensor (4) is connected to a control unit (10) with a fiberglass cable (5).