Recently, we realized a prototype matrix transducer consisting of 48 rows of 80 elements on top of a tiled set of Application Specific Integrated Circuits (ASICs) implementing a row-level control connecting one transmit/receive channel to an arbitrary subset of elements per row. A fully sampled array data acquisition is implemented by a column-by-column (CBC) imaging scheme (80 transmit-receive shots) which achieves 250 volumes/second (V/s) at a pulse repetition frequency of 20 kHz. However, for several clinical applications such as carotid pulse wave imaging (CPWI), a volume rate of 1000 per second is needed. This allows only 20 transmit-receive shots per 3D image. In this study, we propose a shifting aperture scheme and investigate the effects of receive/transmit aperture size and aperture shifting step in the elevation direction. The row-level circuit is used to interconnect elements of a receive aperture in the elevation (row) direction. An angular weighting method is used to suppress the grating lobes caused by the enlargement of the effective elevation pitch of the array, as a result of element interconnection in the elevation direction. The effective aperture size, level of grating lobes, and resolution/sidelobes are used to select suitable reception/transmission parameters. Based on our assessment, the proposed imaging sequence is a full transmission (all 80 elements excited at the same time), a receive aperture size of 5 and an aperture shifting step of 3. Numerical results obtained at depths of 10, 15, and 20 mm show that, compared to the fully sampled array, the 1000 V/s is achieved at the expense of, on average, about two times wider point spread function and 4 dB higher clutter level. The resulting grating lobes were at −27 dB. The proposed imaging sequence can be used for carotid pulse wave imaging to generate an informative 3D arterial stiffness map, for cardiovascular disease assessment.

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.

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.

We describe a 3-D multiline parallel beamforming scheme for real-time volumetric ultrasound imaging using a prototype matrix transesophageal echocardiography probe with diagonally diced elements and separated transmit and receive arrays. The elements in the smaller rectangular transmit array are directly wired to the ultrasound system. The elements of the larger square receive aperture are grouped in 4 × 4-element sub-arrays by micro-beamforming in an application-specific integrated circuit. We propose a beamforming sequence with 85 transmit-receive events that exhibits good performance for a volume sector of 60° × 60°. The beamforming is validated using Field II simulations, phantom measurements and in vivo imaging. The proposed parallel beamforming achieves volume rates up to 59 Hz and produces good-quality images by angle-weighted combination of overlapping sub-volumes. Point spread function, contrast ratio and contrast-to-noise ratio in the phantom experiment closely match those of the simulation. In vivo 3-D imaging at 22-Hz volume rate in a healthy adult pig clearly visualized the cardiac structures, including valve motion.