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In most studies on vascular shear wave imaging (SWI), longitudinal section is mainly concerned, and the radial motion and reflected waves are not considered in cross section. It is important to investigate the SWI in cross section when evaluating the anisotropy of the vessel wall or the complete plaque composition. In our previous study, a novel method based on coordinate transformation and directional...
In vivo measurement of the mechanical properties of thin-walled soft tissues (e.g., mitral valve, artery and bladder) and in situ mechanical characterization of thin-walled artificial soft biomaterials in service are of great challenge. Those thin-walled structures are usually pre-stressed to achieve and/or improve their functional performance, which further complicate the inverse analysis to identify...
Cardiac mock models are helpful to develop new imaging methodologies. Although several mock model setups have been proposed, a good model for the development of intra-cardiac flow imaging is missing. The challenge lies in the fact that mimicking realistic flow patterns requires a realistic left ventricular shape as well as valve systems and a fluid with appropriate rheological properties. Moreover,...
Thermal strain imaging (TSI) is promising for lesion targeting and dose control in thermal-based treatment. We previously developed HIFU and temperature sensitive cerasomes (HTSCs) for local chemotherapy of cancer (Liang et al, Acs Nano 2015). However, the temperature within tissues cannot be noninvasively measured in vivo. The aim of this study was to investigate the feasibility of TSI in noninvasive...
Spatial angular compounding (SAC) with plane wave has been proposed to improve the performance of motion and strain estimation at high frame rate. A previous study shows that the accuracy of 2D estimation depends on the number of steering angles, maximum steering angle, and accuracy of axial estimation at different angles (He et al, Ultrasonics 2017). We have demonstrated (Pan et al, TUFFC 2015) that...
Guided wave elastography (GWE) is promising to measure the local arterial stiffness. However, most studies focus on the longitudinal section, with a guided axial wave (GAW). In addition, the dispersion curve of GAW can be well approximated by immersed Lame wave model only at high frequencies (Li et al, UMB 2017). In the transverse section, guided circumferential wave (GCW) can be utilized to obtain...
In most studies on vascular shear wave imaging (SWI), only longitudinal section is mainly concerned, and the radial motion and reflected waves are not considered in cross section. It is important to investigate the SWI in cross section when evaluating the anisotropy of the vessel wall or the complete plaque composition. In our previous study (He et al, UMB 2017), a novel method based on coordinate...
Metasurfaces in metal/insulator/metal configuration have been widely used in photonics, with applications ranging from perfect absorption to phase modulation, but why and when such structures can realize what functionalities are not yet fully understood. Here, we establish a complete phase diagram in which the optical properties of such systems are fully controlled by two simple parameters (i.e.,...
Recently, gradient metasurfaces, have paved a new direction to the field of metamaterial with many remarkable achievements, including generalized Snell's law [1], new bridge to couple surface wave [2], meta-holograms [3], planar optical devices [4, 5], etc‥ In spite of these great developments, there are some aspects of the metasurfaces needed to be improved. For example, most of the previous systems...
Metamaterialsare electromagnetic composites constructed by subwavelength sized microstructures, and thus can exhibit tailored effective permittivity and permeability. Effective-medium theory (EMT) plays a crucial role since it serves as a bridge to link theories, which are frequently conducted on model hypothetical systems, and experiments which are always performed on realistic metamaterial systems...
Metal/insulator/metal metasurfaces have widely applications ranging from perfect absorption to phase modulation, but the mechanism of these functionalities are not yet fully understood. Here, based on a coupled-mode analysis, we establish a complete phase diagram through two simple parameters, which lays a solid basis for realizing functional and tunable photonic devices with such structures.
High frame rate (≤200 Hz) is required in pulse wave imaging (PWI) to estimate regional pulse wave velocity (PWV) of arteries, and can be achieved by sparse imaging or plane wave imaging at the expense of spatial resolution or signal-to-noise ratio (SNR). However, both high temporal and spatial resolution are required when mapping local PWV variations along inhomogeneous arteries. In this study, the...
In this paper, the previously proposed compressed sensing based synthetic transmit aperture (CS-STA) was compared with synthetic transmit aperture (STA), multi-element synthetic transmit aperture (ME-STA) and the conventional focused mode in two different phantoms. The quantitative results of full width at half-maximum (FWHM) and contrast-to-noise ratio (CNR) demonstrated the merits of CS-STA. Besides,...
Combining metasurfaces with gate controlled graphene, we experimentally demonstrate ±180° phase modulation can be realized at certain frequencies in THz domain, and describe a practical scheme to achieve full-range active phase modulation with such graphene metasurfaces.
Compressed sensing (CS) or compressive sampling allows much lower sampling frequency than the Nyquist sampling frequency. In this paper, we propose a novel technique, named compressed sensing based synthetic transmit aperture (CS-STA), to speed up the acquisition of ultrasound imaging. Ultrasound transducer transmits plane wave with random apodizations for several times and receives the corresponding...
We briefly summarize our recent efforts in employing meta-surfaces to control electromagnetic waves, including realizing high-efficiency photonic spin-hall effect and surface-plasmon couplers, and controlling phases with graphene-based meta-surfaces.
Underpinned by the advent of metamaterials (MMs), transformation optics (TO) offers great versatility to design wave-manipulation devices [1,2], such as cloaks, beam shifter, superlenses, impedence-matched hyperlenses, and field rotator. Although TO theory developed vigorously, it's is quite obvious that most TO ideas are very difficult to realize in practice, because of the extreme electromagnetic...
The predictive value of pulse wave velocity (PWV) for various cardiovascular diseases has been demonstrated in many studies. By means of ultrasound imaging, local PWV, instead of global PWV as in conventional methods, can be measured noninvasively. The accuracy and precision of local PWV measurement have not been fully investigated and several key parameters (i.e. frame rate, number of scan lines...
Rupture of atherosclerotic plaques is the key factor leading to ischemic stroke. In conventional ultrasound, B-mode imaging and/or color flow/pulsed wave Doppler can be used to evaluate the stenosis of blood vessels but not the vulnerability of plaques. In this paper, we propose an ultrasound strain rate imaging based indicator called mean maximum strain rate (MMSR) to evaluate the vulnerability of...
In this work, we demonstrate theoretically and experimentally that a specific gradient-index meta-surface can convert a PW to a SW with nearly 100% efficiency. Distinct from conventional devices such as prism or grating couplers, the momentum mismatch between PW and SW is compensated by the reflection-phase gradient of the meta-surface, and a nearly perfect PW-SW conversion can happen for any incidence...
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