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Aluminum nitride (AlN) Lamb wave resonators (LWRs) utilizing the lowest symmetric (S0) mode have attracted much interests since they have high frequencies, low motional impedances, and capability of multiple frequencies on a single chip. However, the transverse spurious modes are often strong in AlN LWR, and largely degrade the performance in application, so suppression the transverse mode is highly...
Fast cardiac imaging using diverging waves (DW) is receiving much attention. Coherent compounding is important to keep spatial resolution and CNR acceptable. Two approaches have been presented in literature to do so: i) the full aperture of the probe is used and the virtual focus is moved along an arc centered at the center of the probe (ARC); ii) a sub-aperture is used and the virtual focus is linearly...
A row-column-addressed (RCA) 2-D array can be interpreted as two orthogonal 1-D arrays. Since the transmit and receive 1-D arrays are orthogonal to each other, only one-way focusing is possible in each transmit or receive plane. By transmitting with row elements and receiving the echoes through column elements, a rectilinear volume in front of the array can be beamformed. This study suggests to use...
Histotripsy uses high-pressure, microsecond-length pulses to generate cavitation microbubbles to fractionate targeted tissue. After the collapse of a cavitation cloud, remnant microbubbles can persist for a second or longer before passively dissolving. These bubbles can act as seed nuclei for subsequent cavitation events reducing treatment efficiency because the nuclei are not well distributed through...
Pulmonary embolism (PE) is the third-leading cause of death from cardiovascular disease. Currently, PE is treated via catheter-delivered, ultrasound-enhanced thrombolysis using side-fired, low-intensity ultrasound energy (0.5 W/cm2) at ∼2 MHz to reduce the required dose of thrombolytic drugs because of the enhanced drug penetration into the clot. However, several clinical studies have shown that the...
Lateral resolution and therefore image quality in ultrasound is tied to aperture size. While this relationship is understood in ideal imaging conditions, the utility of a large aperture in the presence of clutter is unknown. This problem is particularly relevant to abdominal imaging where thick tissue layers and deep targets create a challenging imaging environment. Previous studies have focused on...
Focused ultrasound can effectively treat tumors by thermal ablation, but treatment times associated with mechanical or electronic scanning of single foci can be prohibitively long. Maximizing the energy efficiency of focused ultrasound ablation may decrease treatment time while also decreasing sensitivity to perfusion. One proposed approach [Mast et al., US Patent 9132287, 2015] creates multiple foci...
Over the course of accelerated failure testing of 2-port SAW delay line resonators on quartz, periodic acoustomigration damage patterns with acoustic apertures of less than 6 wavelengths were observed across the fully metalized region between the transducers, while typical electrode stress damage was observed over the acoustic aperture in the transducer gratings. This suggested the power density had...
Synthetic aperture (SA) ultrasound imaging is a well-known technique in which RF signals for every transmit and receive element combinations is first obtained and a 2-way-focused image is synthetically formed afterwards. Despite its benefits, one of its main shortcomings is reduced penetration depth caused by low acoustic power from single element firing. To address this challenge, we propose a spatial...
Image quality of volumetric intracardiac echocardiography (ICE) catheters is severely limited, especially in the elevation direction, restricted by the catheter diameter. A natural idea is to design a foldable transducer with multiple panes which can be expanded in the heart mechanically to form a large and symmetric 2-D aperture 2–3 times the size of the catheter diameter. Here, the imaging performance...
Ultrafast imaging based on coherent plane-wave compounding improves image quality and allows for much faster acquisition. This method, however, is limited by severe computational loads stemming from delay-and-sum beamforming (DAS BF) that creates a major bottleneck for real-time implementation. Spatial-temporal (ST) processing yields the entire frame without a need for DAS BF of each image line. First,...
RF Voltage transformers operating in one of the ISM frequency bands have recently been demanded in emerging low-power applications, such as wake-up radios in wireless networks, remotely triggered switches, stand-by units in home electronics, etc. S0 Lamb wave resonant (LWR) transformers have been first proposed. Later, SAW transformers designed as “degenerated” CRF have been proposed. Here we demonstrate...
Tissue harmonic imaging, an essential mode of ultrasound imaging scanners, can provide images with high spatial and contrast resolutions. However, it is difficult to use this imaging mode in intravascular ultrasound (IVUS) imaging. This is so because typical IVUS transducers are operated at high frequency (>20 MHz) and have a narrow fractional bandwidth (about 50%). Due to its small aperture (about...
Multi-line transmission (MLT) is a recently developed method for high frame rate cardiac ultrasound imaging. However, a potential pitfall of this method is the presence of artifacts due to cross-talk between the MLT beams. Low complexity adaptive beamforming (LCA) is a high resolution adaptive beamforming method that chooses a weighting function out of a predefined set of apodization functions assembled...
Vector Doppler techniques are ready to substituting the standard methods for blood velocity investigation. However, like in classic Pulse Wave methods, the maximum detectable velocity is related to the Pulse Repetition Frequency (PRF), which is limited by the maximum depth and/or hardware constraints. Unfortunately, the blood velocity, e.g. in stenotic vessels, can easily peak at 2m/s, thus resulting...
Syntethic Aperture Sequential Beamforming (SASB) has been proven to achieve a better resolution and penetration depth than Dynamic Receive Focusing (DRF). SASB has also shown great potential for use in a handheld device. SASB with a low F# (<= 0.5) has shown even better resolution at the cost of high grating lobes, which cause loss of contrast in the final image. The hypothesis is that Spatial...
A challenge in the clinical application of shear wave elastography is the level of measurement variance or noise compared to clinically significant changes in shear wave speed. For instance, liver fibrosis staging is challenged by the relatively high variance of shear wave velocity estimates in comparison to the modulus difference between early (F1-F3) fibrosis stages. Recent work has shown that ultrasound...
The shift to software beamforming has inspired a myriad of adaptive beamformers. Some of these overestimate which signals originate from sidelobes and which originate from the mainlobe. This results in a Dark Region Artifact (DRA) next to hyperechoic targets. We investigate this artifact for seven beamformers: Delay-And-Sum (DAS), the Coherence Factor (CF), Generalized Coherence Factor (GCF), Phase...
All-optical ultrasound imaging, where ultrasound is generated photoacoustically and back-scattered fields are detected with optically resonant structures, has distinct advantages over conventional piezoelectric or capacitive transducers. An absence of electrical connections facilitates probe miniaturisation and confers MRI compatibility, while similar or better sensitivities and bandwidths can be...
Polyvinylidene fluoride (PVDF) and its copolymer (PVDF-TrFE) are known to yield lower electromechanical coupling than ceramic transducers. It is possible to increase transducer efficiency by using two or more PVDF layers with embedded electrodes by configuring the transducer layers in different ways such as folded, barker coded and switchable barker coded [Zhang et al., 1997]. A multi-layer transducer...
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