High-frequency intracoronary ultrasound imaging

Intravascular ultrasound is playing an increasingly important role in the clinical management of coronary interventions. In the past few years the technology for intracoronary ultrasound, in response to clinical pressure, has moved towards lower profile probes with improved handling. While new catheter designs are markedly improved on their predecessors, image quality has not seen significant gains due to the primitive nature of the ultrasound transducer designs. In this article, the potential for improving image quality by increasing the frequency and focusing the ultrasound beam is explored. Basic aspects of transducer implementation are discussed and the acoustic properties of vascular tissues and blood are reviewed. A variety of instruments are used to image coronary and femoral arteries at frequencies ranging from 40 to 200 MHz. These studies serve to illustrate the trade-offs in the development of high frequency IVUS systems. There would appear to be no fundamental reason why frequencies in excess of 50 MHz could not be implemented. Studies using prototype IVUS instruments in the 50 MHz range demonstrate significant improvements in image quality.