http://ieeexplore.ieee.org/iel5/5/31047/01444179.pdf

Fundamentals of acoustics

Advantages and Challenges of Relaxor-PbTiO3 Ferroelectric Crystals for Electroacoustic Transducers- A Review.

Continuous monitoring of the central-blood-pressure waveform from deeply embedded vessels, such as the carotid artery and jugular vein, has clinical value for the prediction of all-cause cardiovascular mortality. However, existing non-invasive approaches, including photoplethysmography and tonometry, only enable access to the superficial peripheral vasculature. Although current ultrasonic technologies allow non-invasive deep-tissue observation, unstable coupling with the tissue surface resulting from the bulkiness and rigidity of conventional ultrasound probes introduces usability constraints. Here, we describe the design and operation of an ultrasonic device that is conformal to the skin and capable of capturing blood-pressure waveforms at deeply embedded arterial and venous sites. The wearable device is ultrathin (240 μm) and stretchable (with strains up to 60%), and enables the non-invasive, continuous and accurate monitoring of cardiovascular events from multiple body locations, which should facilitate its use in a variety of clinical environments.

/pdf/monitoring-of-the-central-blood-pressure-waveform-via-a-205q4e1ldq.pdf

Monitoring of the central blood pressure waveform via a conformal ultrasonic device.

Recent progress in flexible and stretchable piezoelectric devices for mechanical energy harvesting, sensing and actuation

Advances in Piezoelectric Polymer Composites for Energy Harvesting Applications: A Systematic Review

Both optical tweezers and acoustic tweezers have been demonstrated for trapping small particles in diverse biomedical applications. Compared to the optical tweezers, acoustic tweezers have deeper penetration, lower intensity, and are more useful in light opaque media. These advantages enable the potential utility of acoustic tweezers in biological science. Since the first demonstration of acoustic tweezers, various applications have required the trapping of not only one, but more particles simultaneously in both the axial and lateral direction. In this research, a method is proposed to create multiple trapping patterns, to prove the feasibility of trapping micro-particles. It has potential ability to electronically control the location and movement of the particles in real-time. A multiple-focus acoustic field can be generated by controlling the excitation of the transducer elements. The pressure and intensity of the field are obtained by modeling phased array transducer. Moreover, scattering force and gradient force at various positions are also evaluated to analyze their relative components to the effect of the acoustic tweezers. Besides, the axial and lateral radiation force and the trapping trajectory are computed based on ray acoustic approach. The results obtained demonstrate that the acoustic tweezers are capable of multiple trapping in both the axial and lateral directions.

/pdf/feasibility-of-multiple-micro-particle-trapping-a-simulation-5bysx4svv8.pdf

Feasibility of Multiple Micro-Particle Trapping—A Simulation Study

Synthetic transmit aperture (STA) can achieve very high spatial resolution thanks to its dynamic focusing in both transmit and receive. However, because each element is activated individually and sequentially to transmit a spherical wave, the imaging frame rate is low. In addition, the low transmitted energy leads to low signal-to-noise ratio (SNR) echoes. In our previous study, we proposed to use compressed sensing (CS) algorithm to recover full STA dataset from fewer apodized plane wave (PW) transmissions (CS-STA). In this way, the frame rate and SNR of STA imaging can be significantly improved. However, owing to the iterative nature of CS algorithms, the reconstruction of STA dataset is very time consuming, which hampers its real application. In this study, the minimal $l$ 2 -norm least square method is used to recover the STA dataset with significantly reduced computational time. Simulation shows that the proposed method can achieve ~5×103times acceleration for STA dataset reconstruction, compared with CS-STA. Simulated B-mode images show that the proposed method is capable of achieving higher generalized contrast-to-noise ratios (gCNRs) for anechoic inclusions than STA, with maintained spatial resolution. Simulated strain images show that the proposed method could preserve the phase information of radio-frequency data during the reconstruction, and achieve acceptable quality in strain estimation in noise-free condition.

Partial Hadamard Encoded Synthetic Transmit Aperture for High Frame Rate Imaging with Minimal l 2 -Norm Least Square Method

Many methods have been developed to quantify skeletal muscle stiffness. One major limitation is their measurement ranges cannot meet the requirement under maximum voluntary contraction (MVC) condition. The muscle stiffness at high intensity contraction is more important but was rarely reported to be assessed. Furthermore, the dependences of gender and age on the relationship between muscle stiffness and contraction intensity were also not studied systematically. To fix these gaps, an improved vibro-ultrasound system was developed and used to assess the shear modulus of vastus intermedius (VI) along the muscle action direction. Forty healthy subjects volunteered to participate and were divided into four groups: young males, young females, elder males and elder females. Measurements were performed over the entire range of isometric contraction, from 0% to 100% MVC (totally 11 levels). The relationship between muscle stiffness and step isometric contraction level, and the gender and age dependences of this relationship were studied. In addition, VI stiffness was compared with the surface electromyography (EMG) collected from vastus lateralis (VL). Our results showed that VI stiffness was positively correlated to the step isometric contraction level over the entire range (p <; 0.001). Under relaxed condition there was no significant difference between VI stiffness of different genders (p = 0.156) and age ranges (p = 0.221). However, when performing isometric contraction, VI stiffness of male subjects was larger than that of females (p <; 0.001), and that of young subjects was larger than that of elders (p <; 0.001). A high correlation was also found between VI stiffness and the neuromuscular activity of VL. These results can provide complementary information of muscle mechanical properties, and help us to further understand the muscle recruitment strategies of the people with different genders and age ranges under different isometric contraction levels.

Using vibro-ultrasound method to assess the vastus intermedius stiffness over the entire range of step isometric contraction of knee extensors

Ultrasound image plays an important role in the diagnosis of thyroid disease. Accurate segmentation and classification of thyroid nodules are challenging due to their heterogeneous appearance. In this paper, we propose an efficient cascaded segmentation framework and a dual-attention ResNet-based classification network to automatically achieve the accurate segmentation and classification of thyroid nodules, respectively. We evaluate our methods on the training dataset TN-SCUI 2020 Challenge. The 5-fold cross validation results demonstrate that the proposed methods achieve average IoU of 81.43% in segmentation task, and average F1 score of 83.22% in classification task. Finally, our method ranks the first place of segmentation task on the test set through the final online verification. The source code of the proposed methods is available at https://github.com/WAMAWAMA/TNSCUI2020-Seg-Rank1st.

Automatic Segmentation and Classification of Thyroid Nodules in Ultrasound Images with Convolutional Neural Networks

Quantitatively assessing the tissue stiffness with acoustic radiation force impulse (ARFI) method has proved its worth in clinical trials. Much attention has been focused on the research of the displacement estimation algorithm in ARFI. However, the subsequent shear wave speed estimation part can also affect the accuracy and reliability of the results. In this study, several algorithms for shear wave speed estimation were designed and compared using the ultrasound radio-frequency data collected from a self-developed ARFI system. These RT based algorithms were classified as two types: the transformation being performed on the time-location displacement matrix or on the time-depth displacement matrix. The algorithms in Type I attempt to find the best trajectory of the shear wave propagation in one depth, while those in Type II try to directly find the time points when the wavefront passed each lateral location in the whole depth range. Experiments were performed on soft tissue mimicking phantom and ex vivo pork tissue sample. The reliability of repeated measurements and the computation time of these algorithms were compared to find the most stable and time-saving one for ARFI. The results can give us inspiration on how to design a better algorithm for shear wave speed estimation and help to improve the measurement reliability of ARFI.

Weibao Qiu

Papers

Feasibility of Multiple Micro-Particle Trapping—A Simulation Study

Partial Hadamard Encoded Synthetic Transmit Aperture for High Frame Rate Imaging with Minimal l 2 -Norm Least Square Method

Using vibro-ultrasound method to assess the vastus intermedius stiffness over the entire range of step isometric contraction of knee extensors

Automatic Segmentation and Classification of Thyroid Nodules in Ultrasound Images with Convolutional Neural Networks

Comparative study on shear wave speed estimation algorithms in ARFI for improving its reliability