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.

3-D contrast enhanced ultrasound enables better visualization of inherently 3-D vascular geometries compared to an intersecting plane. Additionally, it would allow the application of motion correction techniques for all directions. Both contrast detection and motion correction work better on high-frame rate data. However high-frame rate 3-D ultrasound imaging with dense matrix arrays is challenging to realize. Sparse arrays alleviate some of the limitations in cable count and data rate that fully populated arrays encounter, but their increased level of secondary lobes negatively impacts image contrast. Meanwhile the use of unfocused transmit beams needed to achieve highframe rates negatively impacts resolution. Here we propose to use adaptive beamforming by deep learning (ABLE) to improve the image quality of contrast enhanced ultrasound images acquired with a sparse spiral array. We train the neural network on simulated data and evaluate simulated images and in vivo images of an ex ovo chicken embryo. ABLE improved resolution compared to delay-and-sum (DAS) and spatial coherence (SC) beamforming on the simulated and in vivo data. The qualitative improvements persist after histogram matching, indicating that the image quality improvement of the ABLE images was not purely due to dynamic range stretching.

In this paper, a compact high-voltage (HV) transmit circuit for dense 2D transducer arrays used in 3D ultrasonic imaging systems is presented. Stringent area requirements are addressed by a unipolar pulser with embedded transmit/receive switch. Combined with a capacitive HV level shifter, it forms the ultrasonic HV transmit circuit with the lowest reported HV transistor count and area without any static power consumption. The balanced latched-based level shifter implementation makes the design insensitive to transients on the HV supply caused by pulsing, facilitating application in probes with limited local supply decoupling, such as imaging catheters. Favorable scaling through resource sharing benefits massively arrayed architectures while preserving full individual functionality. A prototype of 8 x 9 elements was fabricated in TSMC 0.18 µm HV BCD technology and a 160 µm x 160 µm PZT transducer matrix is manufactured on the chip. The system is designed to drive 65 V peak-to-peak pulses on 2 pF transducer capacitance and hardware sharing of 6 elements allows for an area of only 0.008 mm 2 per element. Electrical characterization as well as acoustic results obtained with the 6 MHz central frequency transducer are demonstrated.

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