Noninvasive estimation of local speed of sound by pulse-echo ultrasound in a rat model of nonalcoholic fatty liver

Objective: Speed of sound has previously been demonstrated to correlate with fat concentration in the liver. However, estimating speed of sound in the liver noninvasively can be biased by the speed of sound of the tissue layers overlying the liver. Here, we demonstrate a noninvasive local speed of sound estimator, which is based on a layered media assumption, that can accurately capture the speed of sound in the liver. We validate the estimator using an obese Zucker rat model of non-alcoholic fatty liver disease and correlate the local speed of sound with liver steatosis. Approach: We estimated the local and global average speed of sound noninvasively in 4 lean Zucker rats fed a normal diet and 16 obese Zucker rats fed a high fat diet for up to 8 weeks. The ground truth speed of sound and fat concentration were measured from the excised liver using established techniques. Main Results: The noninvasive, local speed of sound estimates of the livers were similar in value to their corresponding "ground truth'' measurements, having a slope ± standard error of the regression of 0.82 ± 0.15 (R2 = 0.74 and p < 0.001). Measurement of the noninvasive global average speed of sound did not reliably capture the ``ground truth'' speed of sound in the liver, having a slope of 0.35 ± 0.07 (R2 = 0.74 and p < 0.001). Decreasing local speed of sound was observed with increasing hepatic fat accumulation (approximately -1.7 m/s per 1% increase in hepatic fat) and histopathology steatosis grading (approximately -10 to -13 m/s per unit increase in steatosis grade). Local speed of sound estimates were highly correlated with steatosis grade, having Pearson and Spearman correlation coefficients both ranging from -0.87 to -0.78. In addition, a lobe-dependent speed of sound in the liver was observed by the ex vivo measurements, with speed of sound differences of up to 25 m/s (p < 0.003) observed between lobes in the liver of the same animal. Significance: The findings of this study suggest that local speed of sound estimation has the potential to be used to predict or assist in the measurement of hepatic fat concentration and that the global average speed of sound should be avoided in hepatic fat estimation due to significant bias in the speed of sound estimate.

Phase-Aberration Correction in Shear-Wave Elastography Imaging Using Local Speed-of-Sound Adaptive Beamforming

Shear wave elasticity imaging (SWEI) is a non-invasive imaging modality that provides tissue elasticity information by measuring the travelling speed of an induced shear-wave. It is commercially available on clinical ultrasound scanners and popularly used in the diagnosis and staging of liver disease and breast cancer. In conventional SWEI methods, a sequence of acoustic radiation force (ARF) pushes are used for inducing a shear-wave, which is tracked using high frame-rate multi-angle plane wave imaging (MA-PWI) to estimate the shear-wave speed (SWS). Conventionally, these plane waves are beamformed using a constant speed-of-sound (SoS), assuming an a-priori known and homogeneous tissue medium. However, soft tissues are inhomogeneous, with intrinsic SoS variations. In this work, we study the SoS effects and inhomogeneities on SWS estimation, using simulation and phantoms experiments with porcine muscle as an abbarator, and show how these aberrations can be corrected using local speed-of-sound adaptive beamforming. For shear-wave tracking, we compare standard beamform with spatially constant SoS values to software beamforming with locally varying SoS maps. We show that, given SoS aberrations, traditional beamforming using a constant SoS, regardless of the utilized SoS value, introduces a substantial bias in the resulting SWS estimations. Average SWS estimation disparity for the same material was observed over 4.3 times worse when a constant SoS value is used compared to that when a known SoS map is used for beamforming. Such biases are shown to be corrected by using a local SoS map in beamforming, indicating the importance of and the need for local SoS reconstruction techniques.

TRAVEL TIME ANALYSIS OF SELECTED URBAN STREETS IN BAGHDAD CITY

Estimating travel time and measuring speed are critical for increasing the efficiency and safety of traffic road networks. This study presents an investigation of arterial travel time estimation for vital routes in Baghdad city. These estimations including speeds, stops, and delays were computed via GPS device and compared to those currently used to quantify congestion and travel time reliability. The study involved a 45-day survey of private vehicles in Baghdad utilizing a Global Positioning System (GPS) probe to collect data on traffic performance metrics for analysis in a GIS context. It was found that the proposed travel time performance measures show definite differences in estimates of peak-hour travel time as compared with weekend travel time. Route (1) from Bayaa intersection - Bab Al-Mutham intersection (through highway) produced a travel time of 165 minutes and 136 minutes for Bayaa intersection - Bab Al-Mutham intersection (through downtown). The travel speed of routes 1 and 2 are observed near 25 kmph which is below the local speed limit of 70 kmph. The maximum travel time of routes 1 and 2 are 71 minutes and 37 minutes, respectively. While delay time was observed 45 and 20 minutes due to traffic congestion on route 1 and 2, respectively. The majority of vehicles are capable of traveling at normal speeds, with relatively few exceeding them.

Light Propagation on a Moving Closed Contour and the Role of Simultaneity in Special Relativity

We consider an example of a moving closed contour and the role played by simultaneity in the description of light propagation on the contour's moving sections. We show that, when constrained to propagate along the contour, the local speed of light on a moving section is no longer arbitrary and a consistent description requires conservation of simultaneity.

PL-TOON: A Low-Cost Experimental Platform for Teaching and Research on Decentralized Cooperative Control

In this paper, we present the development of a low-cost multi-agent system experimental platform for teaching, and research purposes. The platform consists of train-like autonomous agents equipped with local speed estimation, distance sensing to their nearest predecessor, and wireless communications with other agents and a central coordinator. The individual agents can be used for simple PID experiments in a classroom or laboratory setting, while a collection of agents are capable of performing decentralized platooning with cooperative adaptive cruise control in a variety of settings, the latter being the main goal of the platform. The agents are built from low cost components and programmed with open source software, enabling teaching experiences and experimental work with a larger number of agents that would otherwise be possible with other existing solutions. Additionally, we illustrate with experimental results some of the teaching activities that the platform is capable of performing.

Dynamice fracture in a semicristalline polymer: an analysis of the fracture surface

The fracture behaviour of a specific material, a semi-crystalline biobased polymer, was here studied. Dynamic fracture tests on strip band specimens were carried out. Fracture surfaces were observed at different scales by optical and electron microscopy to describe cracking scenarios. Crack initiation, propagation and arrest zones were described. Three distinct zones are highlighted in the initiation and propagation zone: a zone with conical markings, a mist zone and a hackle zone. The conical mark zone shows a variation in the size and density of the conical marks along the propagation path. This is synonymous with local speed variation. Microcracks at the origin of the conical marks in the initiation zone seem to develop from the nucleus of the spherulites. In the propagation zone with complex roughness, the direction of the microcracks and their cracking planes are highly variable. Their propagation directions are disturbed by the heterogeneities of the material. They branch or bifurcate at the level of the spherulites. In the arrest zone, the microcracks developed upstream continue to propagate in different directions. The surface created is increasingly smoother as the energy release rate decreases. It is shown that the local velocity of the crack varies in contrast to the macroscopic speed.

Correlations for calculating the transport and thermodynamic properties of lead-bismuth eutectic

The paper presents recommended correlations for calculating the thermodynamic and transport properties of Pb-Bi eutectic (44.5% Pb + 55.5% Bi), namely: density, dynamic viscosity, specific heat, thermal conductivity, surface tension, specific electrical resistance, and local speed of sound as a function of temperature. These correlations are based on calculated data presented in 39 experimental studies performed in our country and abroad and published during the period from 1923 to 2015. The authors had information on 1103 experimental points; however, a direct assessment was performed on 1076 points. The main difficulty in processing the data was that the experiments considered in the work were performed at different times using a variety of measurement methods, non-unified methods of statistical processing, varying degrees of eutectic purity, etc. The basis of the data estimation technique was the modified least square method, which made it possible to take into account the errors of the experimental data involved. The paper gives the error values of the proposed correlations and the temperature ranges of their applicability. The paper was prepared based on the results of the work of the Thermodynamic Data Center (TDC INPE NRNU MEPhI) of Rosatom State Corporation.

MESOCYCLONE OBSERVATION BY MULTI-PARAMETER METEOROLOGICAL RADAR

The article deals in detail with the case of observation of a cloud array characterized by a large (15 km) height of the upper boundary of cloud cover and the presence of areas with radar reflectivity of more than 60 dBZ by the DMRL-S meteorological radar installed in Valday (Novgorod region). Integrated application of the estimates of all measured parameters makes it possible to identify in this array the area where a rare weather phenomenon - a supercell - develops. The fact of formation of the hail area of large size is ascertained. It leads to the effect of depolarization attenuation - negative values of differential reflectivity of the echo signal of the meteorological targets. The coordinates of vertical flows are determined by analyzing data on the cross-correlation coefficient of polarization constituents of received signal. Then the obtained result is compared with the one obtained by means of estimations of the average radial velocity of particles, their much coincidence being shown. At an altitude of 5 km, areas with sharp local speed changes are observed, indicating the existence of strong vortices. Sequential analysis of the data obtained during the whole time of existence of the supercell leads to identification of a zone 5 km in diameter with a “jump” of magnitude radial velocity of particles in a layer 1 km high at a distance of 100 km. The scale of this zone, its location and the magnitudes of the parameters of the signal received from it indicate the formation of another rare weather phenomenon in it – the mesocyclone