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Future Directions in Intravascular Ultrasound

Intravascular ultrasound imaging requires both a small transducer assembly and catheter delivery system with optimal flexibil‐ ity and steerability. At this moment, multiele‐ ment electronic arrays provide an optimal catheter delivery system but the transducer assembly is both complicated and expensive while the image quality remains rather fair. Most intravascular ultrasound systems use mechanically rotated ultrasound beam generated by a single element. These systems provide good image quality but the need of a drive shaft restricts both the flexibility and steer ability of the catheter delivery system (Table I). In addition, the drive shaft behaves like spring and due to the curved trajectory of the catheter tube in the vascular system, a complicated frictional interaction will occur. The shaft will show a tendency to wind and unwind during one revolution, yielding a certain unpredictability of the angular position of the scanning head relative to that of the proximal system (Fig. 1).1