An Ultrasound Matrix Transducer for High-Frame-Rate 3-D Intra-cardiac Echocardiography.

OBJECTIVE: Described here is the development of an ultrasound matrix transducer prototype for high-frame-rate 3-D intra-cardiac echocardiography. METHODS: The matrix array consists of 16 × 18 lead zirconate titanate elements with a pitch of 160 µm × 160 µm built on top of an application-specific integrated circuit that generates transmission signals and digitizes the received signals. To reduce the number of cables in the catheter to a feasible number, we implement subarray beamforming and digitization in receive and use a combination of time-division multiplexing and pulse amplitude modulation data transmission, achieving an 18-fold reduction. The proposed imaging scheme employs seven fan-shaped diverging transmit beams operating at a pulse repetition frequency of 7.7 kHz to obtain a high frame rate. The performance of the prototype is characterized, and its functionality is fully verified. RESULTS: The transducer exhibits a transmit efficiency of 28 Pa/V at 5 cm per element and a bandwidth of 60% in transmission. In receive, a dynamic range of 80 dB is measured with a minimum detectable pressure of 10 Pa per element. The element yield of the prototype is 98%, indicating the efficacy of the manufacturing process. The transducer is capable of imaging at a frame rate of up to 1000 volumes/s and is intended to cover a volume of 70° × 70° × 10 cm. CONCLUSION: These advanced imaging capabilities have the potential to support complex interventional procedures and enable full-volumetric flow, tissue, and electromechanical wave tracking in the heart.

Imaging Scheme for 3-D High-Frame-Rate Intracardiac Echography: A Simulation Study.

Atrial fibrillation (AF) is the most common cardiac arrhythmia and is normally treated by RF ablation. Intracardiac echography (ICE) is widely employed during RF ablation procedures to guide the electrophysiologist in navigating the ablation catheter, although only 2-D probes are currently clinically used. A 3-D ICE catheter would not only improve visualization of the atrium and ablation catheter, but it might also provide the 3-D mapping of the electromechanical wave (EW) propagation pattern, which represents the mechanical response of cardiac tissue to electrical activity. The detection of this EW needs 3-D high-frame-rate imaging, which is generally only realizable in tradeoff with channel count and image quality. In this simulation-based study, we propose a high volume rate imaging scheme for a 3-D ICE probe design that employs 1-D micro-beamforming in the elevation direction. Such a probe can achieve a high frame rate while reducing the channel count sufficiently for realization in a 10-Fr catheter. To suppress the grating-lobe (GL) artifacts associated with micro-beamforming in the elevation direction, a limited number of fan-shaped beams with a wide azimuthal and narrow elevational opening angle are sequentially steered to insonify slices of the region of interest. An angular weighted averaging of reconstructed subvolumes further reduces the GL artifacts. We optimize the transmit beam divergence and central frequency based on the required image quality for EW imaging (EWI). Numerical simulation results show that a set of seven fan-shaped transmission beams can provide a frame rate of 1000 Hz and a sufficient spatial resolution to visualize the EW propagation on a large 3-D surface.