An intravascular ultrasound catheter system is provided and enables a simplified, economical technique for ultrasound visualization of a blood vessel. The catheter may include a park ablation system for crossing chronic total occlusions and severe stenoses. The catheter is advanceable and is oriented entirely under manual control of the clinician and the application of radiofrequency energy for spark erosion of the stenosis also is controlled manually by the clinician. The system enables the clinician to observe an ultrasound image sufficiently to determine where to orient the ablation electrode so as to reduce the risk of dissection or perforation of the blood vessel. The ultrasound image is generated in response to manual rotation of the catheter and the ablation spark is generated only when the physician is satisfied as to the orientation of the electrode within the vessel.