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

HIGHLIGHTSA dual‐frequency IVUS array transducer is developed for acoustic angiography.The small size is obtained with a reduced form‐factor lateral mode transmitter.The superharmonic imaging is rendered using the Verasonics system.High CNR and good spatial resolution are achieved with 1‐cycle burst excitation. ABSTRACT 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‐&mgr;m‐diameter cellulose tube were measured to be 162 &mgr;m and 1039 &mgr;m, 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 &mgr;m vs 616 &mgr;m). 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.