Dual-frequency intravascular ultrasound transducer design for contrast agent imaging

Abstract

Intravascular ultrasound (IVUS) is a unique diagnostic tool for assessing the composition and degree of stenosis of atheromata in cardiovascular disease. As of yet, contrast enhanced IVUS has not been clinically implemented despite its potential to provide functional information, such as degree of plaque vascularization, in conjunction with standard anatomical mapping. In this study, we demonstrate that nonlinear microbubble signals can be detected with minimal signal processing using an ultra-broadband IVUS transducer composed of a low frequency transmit and a high frequency receive combined element. Raw signals were acquired from a single element transducer (1 × 3 mm, fc = 6.5/35 MHz) after aligning to an acoustically transparent 200 µm inner diameter cellulose tube. Poly-disperse, (1–10 µm diameter) lipid-coated microbubbles were injected at high concentration (4.8 × 108 MBs/mL) and peak negative pressures were varied from −0.3 to −1.8 MPa while transmission cycles were increased from 1to 5. In vitro results indicate signal to noise ratios of 11 dB are attainable at 2nd harmonics and similar SNRs (10–8 dB) at higher harmonics. The results of this study indicate that contrast enhanced IVUS imaging is possible using a single transmit pulsing scheme enabled by using a dual- frequency broadband transducer design.