Development of a focused broadband ultrasonic transducer for high resolution fundamental and harmonic intravascular imaging

Intravascular ultrasound (IVUS) is increasingly employed for detection and evaluation of coronary artery diseases. Tissue Harmonic Imaging provides different tissue information that could additionally be used to improve diagnostic accuracy. However, current IVUS systems, with their unfocussed transducers, may not be capable of operating in harmonic imaging mode. Thus, there is a need to develop suitable transducers and appropriate techniques to allow imaging in multi modes for complementary diagnostic information.;Focused PVDF TrFE transducers were developed using MEMS (Micro-Electro-Mechanical-Systems) compatible protocols. The transducers were characterized using pulse-echo techniques and exhibited broad bandwidth (110% at -6dB) with axial resolutions of <19 micron. These transducers were demonstrated to be suitable for harmonic imaging in IVUS. Improvements in lateral resolution for harmonic signals were investigated. A method was developed to present five modes of images (standard 40 MHz, fundamental 20 MHz (F20), fundamental 40 MHz (F40), harmonic 40 MHz (H40) and harmonic 80 MHz (H80)) using a single transducer. Ex vivo human aorta and coronary ostium were imaged using PVDF TrFE transducers and compared to corresponding images from commercial systems. PVDF TrFE transducers demonstrated improved image quality and showed better definition of the calcific area in the coronary ostium when compared to the corresponding images from current IVUS systems. Standard mode40 MHz images of the human cadaveric aorta were obtained using PVDF TrFE transducers and compared to histology. The images demonstrated near histologic resolution and identified the loose connective tissue and focal necrotic area in the aorta.;Such promising results suggest that focused, broadband PVDF TrFE transducers have opened up the potential to incorporate harmonic imaging modality in IVUS and also improve the image quality. In addition, the transducer's multimodality imaging capability, not possible with the current systems, could enhance the functionality and thereby the clinical use of IVUS.