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

Abstract

Atrial fibrillation (AF) is the most common 1 cardiac arrhythmia and is normally treated by RF ablation. 2 Intracardiac echography (ICE) is widely employed during RF 3 ablation procedures to guide the electrophysiologist in nav-4 igating the ablation catheter, although only 2-D probes are 5 currently clinically used. A 3-D ICE catheter would not only 6 improve visualization of the atrium and ablation catheter, but 7 it might also provide the 3-D mapping of the electromechan-8 ical wave (EW) propagation pattern, which represents the 9 mechanical response of cardiac tissue to electrical activity. 10 The detection of this EW needs 3-D high-frame-rate imaging, 11 which is generally only realizable in tradeoff with channel 12 count and image quality. In this simulation-based study, 13 we propose a high volume rate imaging scheme for a 3-D 14 ICE probe design that employs 1-D micro-beamforming in 15 the elevation direction. Such a probe can achieve a high 16 frame rate while reducing the channel count sufficiently for 17 realization in a 10-Fr catheter. To suppress the grating-lobe 18 (GL) artifacts associated with micro-beamforming in the 19 elevation direction, a limited number of fan-shaped beams 20 with a wide azimuthal and narrow elevational opening angle 21 are sequentially steered to insonify slices of the region of 22 interest. An angular weighted averaging of reconstructed 23 subvolumes further reduces the GL artifacts. We optimize 24 the transmit beam divergence and central frequency based 25 on the required image quality for EW imaging (EWI). Numer-26 ical simulation results show that a set of seven fan-shaped 27 transmission beams can provide a frame rate of 1000 Hz and 28 a sufficient spatial resolution to visualize the EW propaga-29 tion on a large 3-D surface. 30 Index Terms-3-D intracardiac echography (ICE), data 31 rate reduction, electromechanical wave imaging (EWI), high-32 frame-rate ultrasound imaging.

A Pitch-Matched Transceiver ASIC With Shared Hybrid Beamforming ADC for High-Frame-Rate 3-D Intracardiac Echocardiography

“…The imaging frequency has to be determined based on a trade-off between axial resolution and imaging depth and is in this design set to 6 MHz with a depth of 10 cm [17]. Combined with an attenuation coefficient of about 0.5 dB/MHz/cm for heart tissue [39], the attenuation could reach 60 dB.…”

“…2a). The 8×9-element assembly serves as a prototype with an architecture and layout design suitable for scaling to a full array of 64×18 elements [17]. While the prototype has a reduced aperture, it is already tailored towards the intended imaging scheme of acquiring a 70°×70°×10 cm volume in front of the transducer matrix at a frame rate of 1000 volumes/s.…”

“…This effectively reduces the number of connections needed inside the catheter shaft as only the combined signal is transmitted. However, it does not provide the raw data of the full array and introduces focusing errors [17]. These result in increased grating and side lobe levels as well as broadening of the main beam, all negatively impacting image quality.…”

“…Moreover, it allows for the integration of per-element 65-V transmitters [35] and frontends, analog subarray beamformers and digitization in a pitch-matched fashion. The system has a 12-fold data-channel-count reduction, resulting in 96 data channels for the envisioned full system [17]. In a trade-off between the available circuit area and the achievable image quality, the transducer pitch was chosen just above the halfwavelength margin.…”

“…In a trade-off between the available circuit area and the achievable image quality, the transducer pitch was chosen just above the halfwavelength margin. The resulting grating lobe artifacts stay below an acceptable level [17] and can be further reduced through coherent compounding of sub-volume acquisitions [36] and potentially further mitigated through recently shown machine-learning-based image processing techniques [37], [38]. This paper is organized as follows.…”