This paper describes an in-vivo pilot study in which the systolic myocardial stiffness of four pigs was measured with various acoustic techniques. We compare the propagation velocity of shear waves in open chest and closed chest experiments, in which the open-chest shear wave was either physiologically induced by aortic valve closure (N=3), or externally induced by acoustic-radiation force (N=1). The results of closed-chest versus open-chest recordings are consistent within 1 unit of standard error, whereas the acoustic-radiation force measurement showed lowest standard deviation (7% versus 13%).@en

Purpose: To study the feasibility of high-frame-rate (HFR) contrast material-enhanced (CE) ultrasound particle image velocimetry (PIV), or echo PIV, in the abdominal aorta. Materials and Methods: Fifteen healthy participants (six men; median age, 23 years [age range, 18-34 years]; median body mass index, 20.3 kg/m2 [range, 17.3-24.9 kg/m2]) underwent HFR CE US. US microbubbles were injected at incremental doses (0.25, 0.5, 0.75, and 1.5 mL), with each dose followed by US measurement to determine the optimal dosage. Different US mechanical index values were evaluated (0.09, 0.06, 0.03, and 0.01) in a diverging wave acquisition scheme. PIV analysis was performed via pairwise cross-correlation of all captured images. Participants also underwent phase-contrast MRI. The echo PIV and phase-contrast MRI velocity profiles were compared via calculation of similarity index and relative difference in peak velocity. Results: Visualization of the aortic bifurcation with HFR CE US was successful in all participants. Optimal echo PIV results were achieved with the lowest contrast agent dose of 0.25 mL in combination with the lowest mechanical indexes (0.01 or 0.03). Substantial bubble destruction occurred at higher mechanical indexes (>0.06). Flow patterns were qualitatively similar in the echo PIV and MR images. The echo PIV and MRI velocity profiles showed good agreement (similarity index, 0.98 and 0.99; difference in peak velocity, 8.5% and 17.0% in temporal and spatial profiles, respectively). Conclusion: Quantification of blood ow in the human abdominal aorta with US particle image velocimetry (echo PIV) is feasible. Use of echo PIV has potential in the clinical evaluation of aortic disease.@en

Treatment of abdominal aortic (AA) aneurysms and stenotic lesions may be improved by analyzing their associated blood flow patterns. Angle-independent blood flow patterns in the AA can be obtained by combining echo-particle image velocimetry (ePIV) with high frame rate contrast-enhanced ultrasonography. However, ePIV performance is affected by ultrasound contrast agent (UCA) concentration, microbubble stability and tissue clutter. In this study we assessed the influence of acoustic pressure and UCA concentration on image quality for ePIV analysis. We also compared amplitude modulation (AM) and singular value decomposition (SVD) as tissue suppression strategies for ePIV. Fourteen healthy volunteers were imaged in the region of the distal AA. We tested four different UCA bolus volumes (0.25, 0.5, 0.75 and 1.5 ml) and four different acoustic output pressures (mechanical indices: 0.01, 0.03, 0.06 and 0.09). As image quality metrics, we measured contrast-to-background ratio, bubble disruption ratio and maximum normalized cross-correlation value during ePIV. At mechanical indices e 0.06, we detected severe bubble destruction, suggesting that very low acoustic pressures should be used for ePIV. SVD was able to suppress tissue clutter better than AM. The maximum tracking correlation was affected by both UCA concentration and flow rate, where at high flow rates, lower UCA concentrations resulted in slightly higher correlation values but more signal drop-outs during late diastole. High frame rate ePIV was successfully performed in the AA of healthy volunteers and shows promise for future studies in patients.@en

This paper presents a power- and area-efficient front-end ASIC that is directly integrated with an array of 32 × 32 piezoelectric transducer elements to enable the next-generation miniature ultrasound probes for real-time 3-D transesophageal echocardiography. The 6.1 × 6.1 mm2 ASIC, implemented in a low-voltage 0.18 μm CMOS process, effectively reduces the number of cables required in the probe's narrow shaft by means of 96 sub-array beamformers, which have a compact element-matched layout and employ mismatch-scrambling to enhance the dynamic range. The ASIC consumes less than 230 mW while receiving and its functionality has been successfully demonstrated in a 3-D imaging experiment.@en

Purpose: Intraplaque neovascularization (IPN) is an increasingly studied marker of the vulnerable atherosclerotic plaque, and contrast-enhanced ultrasound (CEUS) is an in vivo imaging technique for the assessment of IPN. The purpose of this study was to test novel quantification methods for the detection of carotid IPN using CEUS. Materials and Methods: 25 patients with established carotid atherosclerosis underwent bilateral carotid CEUS using a Philips iU-22 ultrasound system with an L9-3 transducer. Visual scoring of IPN was performed using a 3-point score. Quantification of IPN was performed using novel custom developed software. In short, regions of interest were drawn over the atherosclerotic plaques. After motion compensation, several IPN features were calculated. Statistical analysis was performed using Spearman's rho. Reproducibility of the quantification features was calculated using intra-class correlation coefficients and mean differences between calculations. Results: 45 carotid arteries were available for the quantification of IPN. The quantification of IPN was feasible in all 45 carotid plaques. The IPN area, IPN area ratio and neovessel count had a good correlation with the visual IPN score (respectively ρ=0.719, ρ=0.538, ρ=0.474 all p<0.01). The intra-observer and inter-observer agreement was good to excellent (p<0.01). The intra-observer and inter-observer variability was low. Conclusion: The quantification of carotid IPN on CEUS is feasible and provides multiple features on carotid IPN. Accurate quantitative assessment of IPN may be important to recognize and to monitor changes during therapy in vulnerable atherosclerotic plaques.@en

Ultrafast 3D transesophageal echocardiographic (TEE) imaging, combined with 3D echo particle image velocimetry (ePIV), would be ideal for tracking the complex blood flow patterns in the heart. We are developing a miniature pediatric matrix TEE transducer that employs micro-beamforming (μBF) and allows high framerate in 3D. In this paper, we assess the feasibility of 3D ePIV with a high frame rate, small aperture transducer and the influence of the micro-beamforming technique. We compare the results of 3D ePIV on simulated images using the μBF transducer and an idealized, fully sampled (FS) matrix transducer. For the two transducers, we have simulated high-framerate imaging of an 8.4mm diameter artery having a known 4D velocity field. The simulations were performed in FieldII. 1000 3D volumes, at a rate of 1000 volumes/sec, were created using a single diverging transmission per volume. The error in the 3D velocity estimation was measured by comparing the ePIV results of both transducers to the ground truth. The results on the simulated volumes show that ePIV can estimate the 4D velocity field of the arterial phantom using these small-aperture transducers suitable for pediatric 3D TEE. The μBF transducer (RMSE 44.0%) achieved comparable ePIV accuracy to that of the FS transducer (RMSE 42.6%).@en

In this paper, a programmable time-gain-compensation amplifier dedicated to a 2D piezoelectric ultrasound transducer is presented. It uses an open-loop amplifier structure consisting of a voltage-to-current converter and a current-to-voltage converter. The circuit has been designed in a standard 0.35-μm CMOS process. Simulation and measurement results show that gains of 0dB, 12dB, 26dB and 40dB can be achieved for input signals centered at 6MHz with 80dB dynamic range (100V to 1V). The measured gain errors at 6MHz are below 1dB for all gain settings. The amplifier consumes only 130W when driving a 250f Fload.@en

We consider the scenario of finding the transfer function of an aberrating layer in front of an ultrasound array. We are interested in blindly estimating this transfer function without prior knowledge of the unknown ultrasound sources or ultrasound contrast image. The algorithm gives an exact solution if the matrix representing the aberration layer’s transfer function is full rank, up to a scaling and reordering of its columns, which has to be resolved using some prior knowledge of the matrix structure. We provide conditions for the robustness of blind calibration in noise. Numerical simulations show that the method becomes more robust for shorter wavelengths, as the transfer function matrices then tend to be less ill-conditioned. Image reconstruction from simulated data using the k-Wave toolbox show that a well calibrated model removes some of the distortions introduced by an uncalibrated model, and improves the resolution for some of the sources.@en

This paper presents a pitch-matched transceiver ASIC integrated with a 2-D transducer array for a wearable ultrasound device for transfontanelle ultrasonography. The ASIC combines 8-fold multiplexing, 4-channel micro-beamforming (μ BF) and sub-array-level digitization to achieve a 128-fold channel-count reduction. The μ BF is based on passive boxcar integration and interfaces with a 10-bit 40 MS/s SAR ADC in the charge domain, thus obviating the need for explicit anti-alias filtering and power-hungry ADC drivers. A compact and low-power reference generator employs an area-efficient MOS capacitor as a reservoir to quickly set a reference for the ADC in the charge domain. A low-power multi-level data link concatenates outputs of four ADCs, leading to an aggregate 3.84 Gb/s data rate. Per channel, the RX circuit consumes 2.06 mW and occupies 0.05 mm2. @en

We study the optimal design of an aperture coding mask, and the optimal sensing positions of a single ultrasound sensor with a scanning configuration. In previous works, we have shown that 3D ultrasound imaging is possible using a randomly shaped coding mask with randomly chosen sensing positions. Here we propose an optimization algorithm for the joint design of the coding mask and the sensing positions. We first define a linear measurement model and parameterize it with respect to the mask shape. To optimize the shape of the mask, we use a greedy descent algorithm to minimize the imaging MSE, assuming a Wiener estimate is used for image reconstruction. To optimize the sensing positions, we pre-define a set of such sensing positions by gridding the measurement plane, and regard each sensing position as a virtual sensor candidate. We then use a greedy sensor selection algorithm to find a good selection of sensing positions. To jointly optimize for both the mask and the sensing positions, we alternatingly optimize between them, keeping either the mask shape or the sensing positions fixed. Using simulations we show that the joint optimization results in better imaging performance than optimizing for the mask or the sensing positions alone, or using a completely random design.@en