Dual frequency transducers for intravascular ultrasound super-harmonic imaging and acoustic angiography

Imaging of coronary vasa vasorum may lead to assessment of the vulnerable plaque development in diagnosis of atherosclerosis diseases. Intravascular ultrasound (IVUS) imaging transducers capable of detecting microvessels via nonlinear contrast imaging could provide valuable diagnostic information, however such transducers are not yet produced commercially. Dual-frequency transducers capable of detection of microbubble super-harmonics have shown promise as a new contrast-enhanced IVUS (CE-IVUS) platform. Contrast-to-tissue ratio (CTR) in CE-IVUS imaging can be closely associated with the low frequency transmitter performance. In this paper, multiple dual frequency IVUS transducers with different transmission frequencies (6.5 and 5 MHz) and different materials (PMN-PT single crystals and 1-3 composite) were developed and evaluated. All transducer structures were constructed with the 30 MHz high frequency reception element in front of the low frequency transmission element. Super-harmonic imaging was carried out using a tissue mimicking phantom. With similar peak negative pressures, the lower transmission frequency transducers generated higher CTR (23 dB for 5 MHz transmission). With similar input excitations, the PMN-PT 1-3 composite produced higher resolution (70 μm for 1-cycle burst excitation) than single crystal ones (> 150 μm). Dual frequency transducers with 5 MHz transmitters made of PMN-PT 1-3 composite are preferable in the CE-IVUS imaging.