High Frequency Ultrasound Guidance for Laser Angioplasty

Abstract

Spatial relationships of a laser catheter and vascular anatomy to facilitate laser angioplasty were studied with high frequency ultrasonography in three models: (a) in vitro; (b) in vivo (rabbits), and (c) transcutaneously in humans. The in vitro model consisted of obstructed human cadaver femoral arteries embedded in agar and perfused with diluted blood. The animal model utilized the aortas of 8 anesthetized atherosclerotic rabbits. In these models, the laser delivery system consisted of a 0.2-mm optical fiber connected to a continuous wave neodymium yttrium aluminum garnet laser inserted into an infusion catheter which was advanced through a balloon-tipped guiding catheter to achieve variable coaxial intra-arterial positions. In humans, the laser catheter system alone without laser emissions was inserted percutaneously and imaged by ultrasound in the contralateral femoral artery of patients following coronary arteriography. Ultrasonographic dimensions of in vitro targets and laser created tunnels in these targets correlated with anatomic measurements (r = 0.82 and 0.72, respectively). In vitro and in vivo arterial wall perforations could be recognized and predicted when the fiber tip was positioned eccentrically close to the arterial wall. In 16 patients, the axial position of the balloon and laser catheters could be visualized. Precise definition of lumen surface structure was inadequate. Varying positions of the laser catheter within the artery were recognized in all 3 models. Although ultrasonography cannot presently be applied for all percutaneous transluminal angioplasty approaches, the current study supports the use of developing high frequency ultrasonic guidance for vascular laser systems.