Real-time ultrasound angiography using superharmonic dual-frequency (2.25Â MHz/30Â MHz) cylindrical array: In vitro study

Recent studies suggest that dual-frequency intravascular ultrasound (IVUS) transducers allow detection of superharmonic bubble signatures, enabling acoustic angiography for microvascular and molecular imaging. In this paper, a dual-frequency IVUS cylindrical array transducer was developed for real-time superharmonic imaging. A reduced form-factor lateral mode transmitter (2.25 MHz) was used to excite microbubbles effectively at 782 kPa with single-cycle excitation while still maintaining the small size and low profile (5 Fr) (3 Fr = 1 mm) for intravascular imaging applications. Superharmonic microbubble responses generated in simulated microvessels were captured by the high frequency receiver (30 MHz). The axial and lateral full-width half-maximum of microbubbles in a 200-μm-diameter cellulose tube were measured to be 162 μm and 1039 μm, respectively, with a contrast-to-noise ratio (CNR) of 16.6 dB. Compared to our previously reported single-element IVUS transducers, this IVUS array design achieves a higher CNR (16.6 dB vs 11 dB) and improved axial resolution (162 μm vs 616 μm). The results show that this dual-frequency IVUS array transducer with a lateral-mode transmitter can fulfill the native design requirement (∼3-5 Fr) for acoustic angiography by generating nonlinear microbubble responses as well as detecting their superharmonic responses in a 5 Fr form factor.