Radius Of Scatterer Research Articles

Sticky Hard-Sphere Model for Characterizing Tumor Microstructure via Quantitative Ultrasound.

The use of the structure function (SF) to model interscatterer contribution to ultrasonic scattering is a major step to improve the capability and accuracy of quantitative ultrasound (QUS) and tissue characterization. However, existing QUS-based SF models rely on the hard-sphere (HS) model, which is limited in its applicability for complex scatterer distributions in real tissue. This article introduces the sticky HS (SHS) model for QUS and tissue characterization, which considers a very short-range attractive potential that accounts for the adhesive nature of biological cells and yields a new parameter called stickiness. Herein, the analytical SF expression is presented for monodisperse scatterer size and validated using simulations of scatterer distributions with varying degrees of grouping and volume fractions (0.16, 0.32, and 0.40) over the frequency range from 15 to 110 MHz. The SHS model is applied to three mammary tumor types with differing spatial distributions of tumor cells. The histology-derived SF is computed by considering the nuclei as the main sources of scattering. The results show that the SHS model provides more accurate scatterer radius and volume fraction estimates than the HS model when fit to histology-derived SF versus frequency curves. Furthermore, the new stickiness parameter provided by SHS is sensitive to the grouping structure in tumor cell distribution. This stickiness parameter, combined with the radius and volume fraction estimated from the SHS model, enables better differentiation between different tumor types than using the radius and volume fraction obtained from the HS model. This study demonstrates the potential of the SHS model to improve the QUS tissue characterization.

Direct x-ray scattering signal measurements in edge-illumination/beam-tracking imaging and their interplay with the variance of the refraction signals

X-ray dark-field or ultra-small angle scatter imaging has become increasingly important since the introduction of phase-based x-ray imaging and is having transformative impact in fields such as in vivo lung imaging and explosives detection. Here, we show that dark-field images acquired with the edge-illumination method (either in its traditional double mask or simplified single mask implementation) provide a direct measurement of the scattering function, which is unaffected by system-specific parameters such as the autocorrelation length. We show that this is a consequence both of the specific measurement setup and of the mathematical approach followed to retrieve the dark-field images. We show agreement with theoretical models for datasets acquired both with synchrotron and laboratory x-ray sources. We also introduce a new contrast mechanism, the variance of refraction, which is extracted from the same dataset and provides a direct link with the size of the scattering centers. We show that this can also be described by the same theoretical models. We study the behavior of both signals vs key parameters such as x-ray energy and scatterer radius. We find this allows quantitative and direct scattering measurements during imaging, with implications in all fields where dark-field imaging is used.

A three‐dimensional two‐hemisphere model for unmanned aerial vehicle multiple‐input multiple‐output channels

AbstractThe application of unmanned aerial vehicles (UAVs) has recently attracted considerable interest in various areas. A three‐dimensional multiple‐input multiple‐output concentric two‐hemisphere model is proposed to characterize the scattering environment around a vehicle in an urban UAV‐to‐vehicle communication scenario. Multipath components of the model consisted of line‐of‐sight and single‐bounced components. This study focused on the key parameters that determine the scatterer distribution. A time‐variant process was used to analyze the nonstationarity of the proposed model. Vital statistical properties, such as the space–time–frequency correlation function, Doppler power spectral density, level‐crossing rate, average fade duration, and channel capacity, were derived and analyzed. The results indicated that with an increase in the maximum scatter radius, the time correlation and level‐crossing rate decreased, the frequency correlation function had a faster downward trend, and average fade duration increased. In addition, with the increase of concentration parameter, the time correlation, space correlation, and level‐crossing rate increased, average fade duration decreased, and Doppler power spectral density became flatter. The proposed model was compared with current geometry‐based stochastic models (GBSMs) and showed good consistency. In addition, we verified the nonstationarity in the temporal and spatial domains of the proposed model. These conclusions can be used as references in the design of more reasonable communication systems.

Phononic crystals for sensing FAMEs with demultiplexed frequencies

A numerical investigation on a solid-fluid phononic crystal as a sensor-demultiplexer is presented in order to detect MeCs, including Fatty Acid Methyl Esters group materials - a kind of vegetable oil and basically similar to the fossil fuels. The proposed sensor includes a Mach-Zehnder waveguide with two cavities in which the MeCs are embedded. The cavities contain the target sample and act as frequency resonator. The PnC sensor consists of a square periodic inclusions of Water embedded in stainless steel substrate. Water and stainless steel have a good contrast in physical properties. Therefore, it is possible to have a wide bandgap. To evaluate the band structure and transmission spectrum, the finite element method (FEM) is utilized. Also, the section of demultiplexer acts as a frequency separator for the target sample and finally each of MeCs including MeC 10:0, 12:0 and 14:0 can be sensed based on the relevant frequency extracted from different outputs. The final waveguides are made by changing the radius of scatterers. For each branch, the radii of inclusions are designed to achieve various defect modes. Finally, the Mach-Zehnder sensor-demultiplexer has ability to divide 83.354, 83.361 and 83.367 KHz for MeCs 10:0, 12:0 and 14:0, respectively. To the best of our knowledge, this study is the first to propose a phononic sensor with different outputs for the respective frequencies of various sample combinations.

The effect of scatter correction and radius of rotation on semiquantitative measurements in SPECT 123I-FP-CIT imaging. A phantom study

PurposeThe high energy emissions of 123I and the suboptimal radius of rotation affect the semiquantitative measurements performed during 123I-FP-CIT tomographic imaging. An in-house extra low cost striatum phantom with brain and striatum compartments was constructed and was used to study the effects of Triple Energy Window scatter correction (TEW-SC) and radius of rotation on the Specific Binding Ratio (SBR) measurements. Materials and methodsThe phantom compartments were filled with radioactive 123I solutions with varying concentrations, in a series of experiments. Tomographic images were acquired at six different radii of rotation, with and without TEW-SC and the SBRs were calculated using appropriate regions of interest, as in clinical imaging. ResultsSBRs decreased with increasing radius of rotation in both non-SC and TEW-SC images, the decrease being more pronounced in the latter. The application of TEW-SC increases SBR values by 40% on average. A maximum %Recovery of 42.7% of the true SBR value was achieved in the non-SC images, which increased to 64.6% after TEW-SC. Appropriate correction factors (CF) were calculated in order to make the SBR values independent on the radius of rotation, which could be used to correct SBR values obtained from tomographic acquisitions with suboptimal radius of rotation. ConclusionThe use of appropriate CF can provide more consistent SBR values and a more meaningful comparison between SBRs calculated from images acquired at different radii of rotation.

Optimization scheme of geometric parameters for a 2D locally resonant phononic crystal structure

A ring locally resonant phononic crystal with an effective optimization scheme is proposed. In order to obtain low-frequency broadband properties, three loops of 2-factor (the two key geometric parameters, i.e., the thickness of elastic beam and the radius of scatterer) and 7-level numerical experiments are designed to perform the response surface methodology (RSM) analysis. The low-frequency band gaps (BGs) of the present structures are calculated using finite element method to obtain enough simulation data for RSM analysis. After calculations, the two relationships can be obtained, i.e., the relationship of the starting frequency of the first BG and the two factors; and the relationship of the total bandwidth of the first two BGs and the two factors. Aiming at the lower starting frequency of the first BG and the wider total bandwidth of the first two BGs, the two key geometric parameters are optimized using interior point method.

Polarization ratio characteristics of electromagnetic scattering from sea ice in polar areas**Project supported by the National Key Research and Development Program of China (Grant No. 2016YFC1401007), the Global Change Research Program of China (Grant No. 2015CB953901), the National Natural Science Foundation of China (Grant No. 41776181), and the Postgraduate Research & Practice Innovation Program of Jiangsu Province, China (Grant No.

In the global climate system, the polar regions are sensitive indicators of climate change, in which sea ice plays an important role. Satellite remote sensing is a significant tool for monitoring sea ice. The use of synthetic aperture radar (SAR) images to distinguish sea ice from sea water is one of the current research hotspots in this topic. To distinguish sea ice from the open sea, the polarization ratio characteristics of sea ice and sea water are studied for L-band and C-band radars, based on an electromagnetic scattering model of sea ice derived from the integral equation method (IEM) and the radiative transfer (RT) model. Numerical experiments are carried out based on the model and the results are given as follows. For L-band, the polarization ratio for sea water depends only on the incident angle, while the polarization ratio for sea ice is related to the incident angle and the ice thickness. For C-band, the sea water polarization ratio is influenced by the incident angle and the root mean square (RMS) height of the sea surface. For C-band, for small to medium incident angles, the polarization ratio for bare sea ice is mainly determined by the incident angle and ice thickness. When the incident angle increases, the RMS height will also affect the polarization ratio for bare sea ice. If snow covers the sea ice, then the polarization ratio for sea ice decreases and is affected by the RMS height of snow surface, snow thickness, volume fraction and the radius of scatterers. The results show that the sea ice and the open sea can be distinguished by using either L-band or C-band radar according to their polarization ratio difference. However, the ability of L-band to make this differentiation is higher than that of C-band.

Localized versus delocalized surface plasmons: dual nature of optical resonances on a silver circular wire and a silver tube of large diameter

We investigate the resonances in the scattering and absorption of TE-polarized light by a solid circular silver wire and a silver tube larger than the wavelength radius and nanoscale thickness using the analytical solution and experimental data for the silver complex permittivity. We find that the resonances are well observed both in the visible and infra-red ranges if the scatterer radius is smaller than a certain value. They can be explained as the resonances on the standing surface-plasmon waves running along a curved metal-air interface or a metal layer, respectively. Still, each of them corresponds to one of the multipole localized surface plasmon modes of the circular wire or tube. This bridges the gap between localized and delocalized plasmons, which are complementary descriptions of the same physical effect intrinsic for metals in the visible range.

Ultraslow-light effects in symmetric and asymmetric waveguide structures with moon-like scatterers

Ultraslow-light effects in two-dimensional hexagonal-lattice coupled waveguide with moon-like scatterers were theoretically studied using the plane-wave expansion method. For symmetric structures, simulations showed that slow light with high group index can be achieved by shifting the scatterers and adjusting the radius of moon-like scatterers. The maximum group index was over 8:0 × 104. For asymmetric structures, simulations showed that slow light with flat band and high group index can be obtained by shifting the scatterers, adjusting the radius of moon-like scatterers, and rotating the scatterers. The maximum group index was over 5:7 × 105 with a “saddle-like” relationship between the frequency and group index.

Scatterer size estimation using the center frequency assessed from ultrasound time domain data.

Scatterer size estimation is useful when characterizing tissue using ultrasound. In all previous studies on scatterer size, the estimations are performed in the frequency domain and are thus subjected to a trade off in time-frequency resolution. This study focused on the feasibility of estimating scatterer size in the time domain using only the ultrasound center frequency, assuming a Gaussian-shaped pulse. A model for frequency normalization was derived and the frequency-dependent attenuation was compensated. Five phantoms with well-defined sizes of spherical glass beads were made and scanned with two different linear array transducers with variable center frequencies. A strong correlation (r = 0.99, p < 10-19) between the backscattered center frequency and the product between the wave number and scatterer radius was demonstrated. On average the scatterer diameter was underestimated by 6% ± 24%. These results suggest that estimation of scatterer size is possible using only the center frequency assessed in the time domain.

High-Frequency Quantitative Ultrasound Spectroscopy of Excised Canine Livers and Mouse Tumors Using the Structure Factor Model.

Three scattering models were examined for characterizing ex vivo canine livers and HT29 mouse tumors in the 10-38- and the 15-42-MHz frequency bandwidth, respectively. The spherical Gaussian model (SGM) and the fluid sphere model (FSM) that were examined are suitable for dealing with sparse media, whereas the structure factor model (SFM) is adapted for characterizing concentrated media. For the canine livers, the scatterer radius and the acoustic concentration estimated with the three models were similar and matched well the nuclear structures obtained from histological analysis (with relative errors less than 7%). These results show that the livers could be considered as a diluted medium and that the nuclei in liver could be a dominant source of scattering. For the homogeneous mouse tumors, containing mostly viable HT29 cells, scatterer radius and volume fraction estimated with the SFM showed good agreement with the whole cell structures obtained from histological analysis (with relative errors less than 15%), whereas the sparse models (the SGM and the FSM) gave no consistent quantitative ultrasound parameters. This suggests that the viable HT29 cell areas have densely packed cellular content and that the whole HT29 cell could be responsible for scattering. For the heterogeneous tumors, the hyperechogenic zones observed in the B-mode images were linked to the presence of small necrotic areas surrounded by viable HT29 cells. Comparison between sparse and concentrated models shows that these hyperechogenic zones could be considered as a concentrated medium.

Tunable multiple Fano resonances in magnetic single-layered core-shell particles

We investigate multiple Fano, comblike scattering resonances in single-layered, concentric core-shell nanoparticles composed of magnetic materials. Using the Lorenz-Mie theory, we derive, in the long-wavelength limit, an analytical condition for the occurrence of comblike resonances in the single scattering by coated spheres. This condition establishes that comblike scattering response uniquely depends on material parameters and thickness of the shell, provided that it is magnetic and thin compared to the scatterer radius. We also demonstrate that comblike scattering response shows up beyond the long-wavelength limit and it is robust against absorption. Since multiple Fano resonances are shown to depend explicitly on the magnetic permeability of the shell, we argue that both the position and profile of the comblike, morphology-dependent resonances could be externally tuned by exploiting the properties of engineered magnetic materials.

Temporal properties of random lasers under ultrashort pulse excitation

Temporal properties of random lasing under ultrashort pulse excitation are investigated in a two-dimensional disordered medium. The pumping light is described individually and coupled into the rate equations. The Maxwell equations and rate equations are numerically solved by using the finite-difference time domain method. The time evolution of the emission pulse is studied with the variation of the surface-filling fraction, refractive index, and scatterer radius. Results show that the behavior of random lasing depends strongly on the sample parameters. Our work enriches the knowledge about random lasers in the ultrashort pulse pumping regime and offers some guidance for relevant experiments.

Application of the polydisperse structure function to the characterization of solid tumors in mice

A polydisperse structure function model has been developed for modeling ultrasonic scattering from dense scattering media. The polydisperse structure function is incorporated to a fluid-filled sphere scattering model to model the backscattering coefficient (BSC) of solid tumors in mice. Two types of tumors were studied: a mouse sarcoma (Englebreth-Holm-Swarm [EHS]) and a mouse carcinoma (4T1). The two kinds of tumors had significantly different microstructures. The carcinoma had a uniform distribution of carcinoma cells. The sarcoma had cells arranged in groups usually containing less than 20 cells per group, causing an increased scatterer size and size distribution. Excised tumors (13 EHS samples and 15 4T1 samples) were scanned using single-element transducers covering the frequency range 11–105 MHz. The BSC was estimated using a planar reference technique. The model was fit to the experimental BSC using a least-square fit. The mean scatterer radius and the Schulz width factor (which characterizes the width of the scatterer size distribution) were estimated. The results showed significantly higher scatterer size estimates and wider scatterer size distribution estimates for EHS than for 4T1, consistent with the observed difference in microstructure of the two types of tumors. [Work supported by NIH CA111289.]

Comparison of photonic bandgaps of two-dimensional periodic and quasi-periodic photonic crystals with different relative permittivity dielectric

Photonic bandgaps (PBGs) of two-dimensional (2D) triangular-lattice and square-lattice and decagonal quasi-periodic photonic crystals (PCs) have been analyzed, with a given scatterer radius and dielectric relative permittivity changing from 1 to 30 within air-cylinders-in-dielectric and dielectric-cylinders-in-air constructions. The results have shown that 2D quasi-periodic PC is more likely to generate PBG and complete PBG than 2D periodic PC. For the given scatterer radius and two constructions, PBG widths of the two types of 2D PCs vary little, whereas the corresponding center frequencies decrease in smooth “hyperbola-like” curves with dielectric relative permittivity increasing monotonically. The present results will guide the design of PBG-type microstructure photonic devices.

Mode competition of bichromatic laser emission in two-dimensional strong scattering random medium

The mode competition of the bichromatic laser emission in two-dimensional (2D) random medium was studied. Based on the time-dependent theory, a model for dual-wavelength random laser was established. The Maxwell equations and rate equations were combined and solved by using the finite different time domain (FDTD) method. Results show that the emission intensity of both wavelength ranges increases simultaneously with the increasing of the surface-filling fraction. The mode dominance of the bichromatic emission can be switched by changing the scatterer radius. The emission intensity of the longer wavelength increases when enlarging the excitation area. The controllability of these lasing modes may provide a potential application of optical switches.

Analysis of Center Detonation Characteristics of Water Mist

This paper analyzed the formula for calculating the velocity and scatter radius of water mist droplets after detonation. Through establishing model, calculating by the formula and simulation of theoretical model, the reasons of deviation between calculation and simulation results were found out. In order to make theoretical calculation more accurate and applicable, new formula was created by introducing correction factors.

Two-dimensional photonic quasicrystal flat lens with three scatterers

A two-dimensional (2-D) photonic quasicrystal (PQC) flat lens with three scatterers is proposed, and its focusing characteristics for a point source are analyzed for the case of a continuously changing scatterer radius. The results show that a super-lens can be formed by three scatterers, and there is a threshold for scatterer radius. The focusing characteristics of the flat lens within the focusing radius are changed with regularity. It is reported for the first time that best image quality and the stability of perfect imaging in this 2-D PQC flat lens with three scatterers are superior to those in 2-D PQC or periodic photonic crystal flat lenses with multiple scatterers.

Hysteretic characteristics of 1/λ^4 scattering of light during adsorption and desorption of water in porous Vycor glass with nanopores

Porous Vycor glass with nanopores is transparent in the visible region and is often used in colorimetric chemical sensing when impregnated with selectively reacting reagents. However, it has some disadvantages in sensing, since changes in the humidity of ambient air strongly affect its transmission. In this work, by combining a humidity-controlled thermostatic chamber and an ultraviolet-visible and near-infrared spectrophotometer through fiber optics, we analyzed the effect of increasing and decreasing humidity in the ambient air on the transparency change of the nanoporous glass. The transparency response in the visible region to changes in humidity is analyzed to correlate the turbidity response of the glass with the amount of water in it. The turbidity is found to be dependent on the inverse fourth power of the wavelength (1/λ⁴), which implies that Rayleigh-type scattering takes place for both adsorption and desorption of water. We show that measures of the extent of the optical inhomogeneity that causes the scattering, such as the effective radius of scatterers and their number density, exhibit a pronounced hysteretic characteristic for the imbibition and drainage of water, while the absorption inherent to imbibed water also shows another type of hysteresis that is quite similar to the sorption isotherms of water. On the basis of the above observations, we show that the transitory white turbidity of nanoporous glasses during changes in humidity can be consistently interpreted and quantitatively analyzed by a simple Rayleigh scattering mechanism.

Scatterer radius dependence of focusing properties in two-dimensional photonic quasicrystal flat lens

The focusing properties of a germanium decagonal photonic quasicrystal flat lens with different scatterer radii have been analyzed. For different wavelengths and polarization modes, the lenses have different scatterer radius thresholds resulting in different focusing properties. For a point source of light in the transverse-electric mode, we found dual-focusing occurs along the symmetry axis within a range of scattering radii. As scatterer radius increases, the dual-focusing image power and far-field-focusing image quality diminish, whereas near-field-focusing image quality, dual-focusing image distance, and the summed object-image distance all increase.