High frequency focal transducer with a Fresnel zone plate for intravascular ultrasound

Abstract

The diameter of an intravascular ultrasound (IVUS) catheter is always less than 1 mm, because it must be inserted into a blood vessel to obtain ultrasound images. Owing to this requisite small size, it is difficult to perform geometric focusing on the surface of an IVUS transducer to improve the spatial resolution of the image. This study proposes a high frequency transducer with a Fresnel zone plate (FZP) for intravascular ultrasound imaging. Through theoretical calculations, the parameters and structure of the transducer are optimized for high-frequency ultrasound. The acoustic beam is simulated using COMSOL software. The aperture size of the ultrasound element is 0.778 × 0.9 mm2. Transducers with or without the FZP layer are designed and fabricated in this study. The center frequency and –6 dB bandwidth of the FZP transducer are 52.5 MHz and 42%, respectively. Meanwhile, the center frequency and –6 dB bandwidth of the plane-shape transducer are 51.3 MHz and 58%, respectively. Wire phantom and porcine artery imaging experiments were performed to evaluate the performance of the designed transducers. The spatial resolution of the FZP transducer is 46.8 μm axially and 183.6 μm laterally, and the resolution of the plane-shape transducer is 44.3 μm axially and 313.5 μm laterally. The results demonstrate that the FZP transducer provides superior lateral imaging resolution for IVUS applications.