Backscatter Levels Research Articles

One-step Physical Method for Synthesis of Cu Nanofluid in Ethylene Glycol

The Cu nanofluid in ethylene glycol was prepared by electrical explosion of wire, a novel one-step method. The X-ray diffraction, field emission scanning electron microscope and transmission electron microscope were used to study the properties of Cu nanoparticles. The results showed that the nanoparticles were consisted of pure face-centered cubic structure and near spherical shape with average grain size of 65 nm. Ultraviolet-visible spectroscopy (UV-Vis) confirmed Cu nanoparticles with a single absorbance peak of Cu surface plasmon resonance band at 600 nm. The nanofluid was found to be stable due to high positive zeta potential value, +51 mV. The backscattering level of nanofluid in static stationary was decreased about 2% for 5 days. The thermal conductivity measurement showed that Cu-ethylene glycol nanofluid with low concentration of nanoparticles had higher thermal conductivity than based fluid. The enhancement of thermal conductivity of nanofluid at a volume fraction of 0.1% was approximately 5.2%.

The spatial correlation of backscattered ultrasonic grain noise: theory and experimental validation

In ultrasonic pulse/echo inspections of metals, backscattered grain noise signals observed at different nearby transducer positions will be correlated. Such correlations have important practical implications. For example, the spatial correlation length (SCL) of the backscattered noise is a crucial quantity in designing denoising algorithms for image processing, and in inspection simulations of the probability of detection (POD) of a defect. In this paper an existing theory for the average backscattered grain noise level, based on the single scattering assumption and the Born approximation, is extended to obtain a formal theory for the spatial correlation of the backscattered grain noise. A special form of the theory for an incident Gaussian sound beam is also presented to demonstrate that the specimen microstructure and an overlap integral for the incident sound field are the important physical parameters controlling the grain noise level and spatial correlation, respectively. To validate the theory, a series of experiments are performed to collect backscattered grain noise signals from nickel alloy specimens having equiaxed microstructures. Good agreement between measured and predicted correlations is generally found. Further model computations are performed to better illustrate how amplitude and phase variations within the incident sound field control the dependence of the grain noise spatial correlation upon transducer separation.

Propagative Landau States and Fermi Level Pinning in Carbon Nanotubes

We present strong evidence of Landau states formation in multiwalled carbon nanotubes with metallic or semiconducting outer shells, under magnetic fields as high as 60 T. Magnetoconductance data are found to converge to a gate-independent value for semiconducting shells, whereas for metallic shells, the Landau states introduce a strong reintroduction of backscattering and Fermi level pinning close to the charge neutrality point. Electronic band structure and transport calculations provide a consistent interpretation of the experimental data.

Signatures of ALOS PALSAR L-Band Backscatter in Swedish Forest

The Phased Array type L-band Synthetic Aperture Radar onboard the Advanced Land Observing Satellite has, since its launch, been acquiring an extensive data set of images over two forest test sites in Sweden. The sites of Remningstorp (Lat. 58deg30' N, Long. 13deg40' E) in the south and Krycklan (Lat. 64deg14' N, Long. 19deg50' E) in the north of Sweden are characterized by hemiboreal and boreal forests, respectively. In this paper, we have investigated the signatures of standwise backscatter measurements from forests with different growth stages in relation to polarization, environmental conditions, image viewing geometry, and spatial resolution. The HV backscatter presented stronger sensitivity to the forest growth stage than the HH and VV backscatter. Under unfrozen conditions, the dynamic range of fine-beam data acquired at 34.3deg was 8-9 dB for the HV polarization and 6-7 dB for the HH polarization. At 21.5deg, in the polarimetric mode, the dynamic range was 6, 7, and 9 dB at VV, HH, and HV polarizations, respectively. Regardless of the specific polarization, the backscatter was temporally consistent under unfrozen conditions, with a small increase of backscatter in regrowing young forest for wet conditions. Under thawing and frozen conditions, repeated measurements were available only for the HH backscatter at 34.3deg. For thawing conditions, the backscatter level was similar to the unfrozen conditions even though the signatures differed depending on temperature dynamics, snow-cover properties, and precipitation. Under frozen conditions, the signatures varied depending on temperature. For images acquired when the temperature was well below the freezing point, the backscatter was low, and the dynamic range was small (2-4 dB); nonetheless, the measurements were consistent. Images acquired when temperature was close to the freezing point presented a behavior similar to unfrozen conditions. The sensitivity of the backscatter to the image viewing geometry for different growth stages was studied for data acquired under dry unfrozen conditions. The backscatter difference increased for increasing look angle because of the increase in volume scattering and the decrease of ground-surface backscatter. The largest difference was observed at 41.5deg with 2.5-4-dB difference for the HH and 4-5-dB difference for the HV case. Loss of spatial resolution (20-50 m) did not have any effect on the backscatter signatures in Krycklan, whereas in Remningstorp, the smallest stands were affected.

Impact of Rayleigh backscattering on Stimulated Brillouin Scattering threshold evaluation for 10 Gb/s NRZ-OOK signals

At bit rates comparable with the Brillouin shift, i.e. higher than 10 Gbit/s, the signal and the Brillouin backscattered spectra partially overlap. This implies an interaction between different scattering phenomena occurring through out the optical fiber. In particular we believe that an evaluation of how Rayleigh backscattered components of the modulated signal are subjected to Stokes gain is required. This interaction may lead to an increased backscattered power, which in turn will affect Brillouin threshold estimation. We experimentally verified a decrease of Stimulated Brillouin Scattering (SBS) threshold for 10 Gb/s NRZ-OOK signals with respect to theoretical predictions. Simulations carried out with a numerical model of SBS, accounting for Rayleigh contributions, well predict measured backscattered power levels. On the other hand we also experimentally verified that this SBS threshold decrease does not degrade transmission system performance. Indeed, measured BER curves put into evidence a penalty reduction for signal powers just before the saturation regime, which should be usefully taken into consideration in optical systems power budget planning.

Quantitative Analysis of the Magnitude and Time Delay of Cyclic Variation of Myocardial Backscatter from Asymptomatic Type 2 Diabetes Mellitus Subjects

Early detection of diabetic patients at high risk for developing diabetic cardiomyopathy may permit effective intervention. The goal of this work is to determine whether measurements of the magnitude and time delay of cyclic variation of myocardial backscatter, individually and in combination, can be used to discriminate between subgroups of individuals including normal controls and asymptomatic type 2 diabetes subjects. Two-dimensional parasternal long-axis echocardiographic images of 104 type 2 diabetic patients and 44 normal volunteers were acquired. Cyclic variation data were produced by measuring the mean myocardial backscatter level within a region-of-interest in the posterior wall, and characterized in terms of the magnitude and normalized time delay. The cyclic variation parameters were analyzed using Bayes classification and a nonparametric estimate of the area under the receiver operating characteristic (ROC) curve to illustrate the relative effectiveness of using one or two features to segregate subgroups of individuals. The subjects were grouped based on glycated hemoglobin (HbA1c), the homeostasis model assessment for insulin resistance (HOMA-IR) and the ratio of triglyceride to high-density lipoprotein cholesterol (TG/HDL-C). Analyses comparing the cyclic variation measurements of subjects in the highest and lowest quartiles of HbA1c, HOMA-IR and TG/HDL-C showed substantial differences in the mean magnitude and normalized time delay of cyclic variation. Results show that analyses of the cyclic variation of backscatter in young asymptomatic type 2 diabetics may be an early indicator for the development of diabetic cardiomyopathy. (E-mail: james.g.miller@wustl.edu)

Lymph node micro-architecture can be imaged using optical coherence tomography.

Abstract Abstract #804 Background: Histological assessment is the gold standard technique for identification of lymph node involvement in breast cancer. However, this may only be performed ex vivo and will often result in the unnecessary excision of healthy lymph nodes. In axillary clearance, this will result in lymphedema in approximately 26% of patients. Optical Coherence Tomography (OCT) is a real-time imaging modality with the potential to perform in vivo optical biopsy of lymph nodes. We undertook ex vivo imaging of excised lymph nodes to identify which aspects of the lymph node micro-architecture could be imaged using OCT, and to identify differences between cancerous and normal nodes.
 Materials and Methods: 18 lymph nodes were taken from 13 patients undergoing axillary clearance or sentinel lymph node biopsy. Fresh excised lymph tissue was dissected into 2mm slices. A 3D-OCT scan was acquired, with a resolution of ∼11μm in both axial and lateral dimensions. Each sample underwent subsequent histological analysis using Haematoxylin and Eosin (H&E) staining and matched against the 3D-OCT data sets.
 Results: OCT images demonstrated differentiation of the three major tissue types found in the lymph node: adipose, lymph cortex and lymph capsule. Adipocytes demonstrated a characteristic honeycomb structure that was also visible in H&E stained histology. The cortex, containing a high concentration of lymphocytes, was found to give a strong level of optical backscatter in the OCT image. The capsule, consisting of less dense stroma tissue, could generally be differentiated from the cortex. Small blood vessels in the stroma and cortex presented as areas of low backscatter. Sinuses were identified as contributing to variation in intensity within the cortex. Germinal centers could be distinguished from resting lymphoid tissue by a characteristic circular structure apparent in both OCT and histology. Cancerous regions were found to be devoid of these characteristic micro-architectural structures, as the malignant cells replaced normal lymph tissue. Figure 1 shows the H&E histology image and corresponding OCT scan of a normal lymph node. Adipose, cortex, stroma and small blood vessels are all apparent in this sample.
 Discussion: These results demonstrate that OCT is able to differentiate relevant structures within lymph nodes. Our findings suggest that lymph node metastasis is evident by the lack of these structures. This corresponds well with histological findings. This work forms a basis for future in vivo studies aimed at assessing lymph node involvement prior to excision.
 
 Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 804.

Intrinsic Myoarchitectural Differences Between the Left and Right Ventricles of Fetal Human Hearts: An Ultrasonic Backscatter Feasibility Study

Embryologically, cardiac chambers differ in their morphologic and contractile properties from the beginning. We hypothesized that a noninvasive ultrasonic backscatter investigation might illustrate the fundamental differences in myocardial morphologic properties of the 2 ventricles during heart development. The goals of this investigation were to 1) explore the feasibility of measuring the magnitude of cyclic variation of ultrasonic backscatter from the left and right ventricular free walls of fetal hearts; 2) compare measurements of the magnitude of cyclic variation from the left and right sides of the heart; and 3) determine if the observed results are consistent with predictions relating the overall backscatter level and the magnitude of cyclic variation. Cyclic variation data from the left and right ventricular free walls were generated from analyses of the backscatter from echocardiographic images of 16 structurally normal fetal hearts at mid-gestation. The magnitude of cyclic variation was found to be greater for the left ventricular free wall than for the right ventricular free wall (4.5 +/- 1.1 dB vs 2.3 +/- 0.9 dB, respectively; mean +/- standard deviation; P < .0001, paired t test). Measurements of the cyclic variation of backscatter can be obtained from both the left and right sides of fetal hearts demonstrating a significant difference between the measured magnitude of cyclic variation in the left and right ventricular myocardium. This observation is consistent with predictions relating the overall backscatter level and the magnitude of cyclic variation. The results of this study suggest cyclic variation measurements may offer a useful approach for characterizing intrinsic differences in myocardial properties of the 2 ventricles in assessing fetal heart development.

Scattering by unexploded ordnance with variable burial depth and seafloor roughness: A parametric study.

Efficient search strategies for unexploded ordnance (UXO) by sonar greatly depend on the ocean environment, particularly bottom roughness, and the mean burial depth of the target. To gain insight into how detection ranges vary with statistical properties of the ocean bottom and factors associated with object burial, we apply full‐wave numerical modeling using the time‐domain elastodynamic finite‐integration technique (EFIT). The numerical technique—which is not restricted to small interface slopes or amplitudes—allows us to obtain a uniform picture of enhancement of acoustic bottom penetration with frequency and roughness parameters, while providing roughness backscattering levels for variable incidence angles. For the target, attention is focussed mostly on scattering near beam incidence, and comparison with experiments is made for a 5‐in. rocket UXO. Good agreement with measured target strength over the 4–30‐kHz band is obtained using a two‐dimensional EFIT model with simple finite‐aperture corrections for three‐dimensional (3‐D) effects. We consider both forward and backscattering and discuss the potential advantages of both. For lower frequencies, we compare with a full 3D finite‐element model which compares favorably with data. [Work supported by SERDP and ONR.]

Long Range and cm-Level Spatial Resolution Measurement Using Coherent Optical Frequency Domain Reflectometry With SSB-SC Modulator and Narrow Linewidth Fiber Laser

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper describes coherent optical frequency domain reflectometry (C-OFDR) with cm-level spatial resolution over 5 km. We propose the use of a single sideband with a suppressed carrier (SSB-SC) modulator and a narrow linewidth fiber laser as a tunable light source for C-OFDR. The advantage of using SSB-SC modulation is clarified theoretically by comparison with a double sideband with suppressed carrier modulation. We achieved cm-level spatial resolution over a 5-km measurement range and high sensitivity with a noise level 30 dB lower than the Rayleigh backscattering level. </para>

Calibrated quantitative ultrasound imaging of skeletal muscle using backscatter analysis

We evaluated the ability of an ultrasound method, which can characterize cardiac muscle pathology and has reliability across different imaging systems, to obtain calibrated quantitative estimates of backscatter of skeletal muscle. Our procedure utilized a tissue-mimicking phantom to establish a linear relationship between ultrasound grayscale and backscatter levels. We studied skeletal muscles of 82 adults: 45 controls and 37 patients with hereditary myopathies. We found that skeletal muscle ultrasound backscatter levels varied with probe orientation, age, and muscle contraction and pathology. Reliability was greater with the probe in longitudinal compared with transverse planes. Backscatter levels were higher in those >40 years of age, in muscle extension than flexion, and in myopathic patients than controls. Calibrated measurements of muscle backscatter have sensitivity and specificity in identifying and reliably measuring levels of skeletal muscle pathology.

Modeling of stimulated Brillouin scattering in expanding plasmas

Numerical simulations of mm-size expanding plasmas have been performed in comparison with recent experiments at the LULI facility. The features of Stimulated Brillouin Scattering (SBS) are studied for an intense mono-speckle laser beam in continuation of previous work on optically smoothed laser beams. Very good agreement between the theoretical-numerical modeling and the experimental results is found, in particular concerning the SBS activity in the plasma and the backscatter level. The results underline the importance of nonlocal transport effects affecting the onset of self-focusing for temperatures below 1keV. The simulations with the monospeckle beam allow to identify the resonant filament instability [1] and the subsequent loss of coherence of the laser beam as the reason of the observed low-level backscatter levels measured in the experiments. To achieve reliable numerical modeling, a good characterisation of the plasma profiles and the timing with respect to the laser pulse shape, prior to simulations, proves to be extremely important.

Analysis of acoustic backscattering from the ocean bottom using radiative transfer theory

Radiative Transfer (RT) theory is a heuristic formulation for analysis of wave propagation in random media based on the principle of conservation of energy rather than on the solution of the wave equation. The theory has been applied to electromagnetics and more recently to ultrasound and seismics, and it has the advantage of being computationally tractable for complex random environments. In this paper the RT formulation is proposed for the problem of layered ocean bottom sediment with random scatterers. The volume backscattering level from tenuous media is obtained by solving the RT equation at each individual layer and by applying the corresponding reflection and transmission coefficients at the rough boundaries. Simulations of the backscattered acoustic intensity from a finite layer with elastic spherical scatterers are presented. The results obtained from the RT equation are compared to those based on the wave equation. Single frequency steady state solutions are considered for different cases of sediment attenuation and layer thickness. The flexibility of the RT method is demonstrated by showing the individual effect of propagating longitudinal and shear waves in the elastic sediment. It is proved that the contribution of shear waves in consolidated sediments is considerable.

The influence of topography on sidescan sonar images

The backscattering signal on sidescan sonar images is to a large degree dependent on the incident angle of the acoustic beam onto the seafloor. As sidescan sonar systems are often used for mapping seafloor lithologies, it is necessary to reduce or even remove the effect of different backscattering strengths caused by varying incidence angles. This study evaluates the influence of seafloor morphology on the acoustic backscattering signal of the deep‐towed IFM‐GEOMAR DTS‐1 sidescan sonar system. Data used are from the Pacific continental slope offshore Nicaragua in a water depth between 800 and 2400 metres. There authigenic carbonate patches formed by cold fluid venting are imaged with a high backscattering level. The carbonates are often located on top or on the flanks of mound structures with a strong morphology. The specific DTS‐1 backscattering function is determined on normal, uniform seafloor sediment, and then applied in a new processing algorithm to the raw data of two test areas. The change in amplitude strength when considering seafloor morphology is calculated. The topographic influence on the backscattering signal can be quite significant when imaging mound structures. Nevertheless the high backscatter on mounds is not completely removed, leading to the conclusion that it originates from a different seafloor lithology and roughness.

Preclinical cardiac involvement in phaeochromocytoma: a study with integrated backscatter

It is well known that vascular and cardiac structure may be influenced by circulating neurohormonal factors. Our aim was to study the myocardial wall texture by integrated backscatter (IBS) analysis in patients with phaeochromocytoma (PHEO). Fourteen patients with PHEO, 15 matched high-normal blood pressure (BP) subjects, 15 mild essential hypertensives and 15 normotensive controls underwent two-dimensional conventional ultrasonography and ultrasonic IBS of the myocardial wall. IBS analysis was performed at both interventricular septum and posterior wall levels. IBS values were expressed in decibels and corrected for the IBS values obtained within the pericardium (C-IBS). The systo-diastolic cyclical variations in IBS (CV-IBS), an index of myocardial contractile performance, were also evaluated. Patients with PHEO showed C-IBS values comparable to those of hypertensive patients, and significantly higher than those of high-normal BP subjects and controls at both septum and posterior wall levels (P < 0.001 for all). In PHEO patients, CV-IBS was lower than that of normotensive, high-normal BP subjects and hypertensive patients, at both septum and posterior wall levels (P < 0.001 for all). An inverse relationship was found in the PHEO group between 24-h urinary normetanephrine and CV-IBS of both septum (r(2) = -0.29, P < 0.05) and posterior wall (r(2) = -0.46, P < 0.05). Our results show that patients with PHEO have myocardial remodelling characterized by increased myocardial fibrosis, confirmed by an increase in the overall myocardial backscatter level measured. The observed decrease in the magnitude of CV-IBS suggests an impairment of myocardial contractile performance. These results may provide insights into the role of catecholamines in left ventricular (LV) structure and function in PHEO.

Control of electron- and phonon-derived thermal conductances in carbon nanotubes

We present a method for controlling the electron- and phonon-derived thermal conductances in carbon nanotubes with vacancy defects involving numerical analysis based on the nonequilibrium electron/phonon Green's function method. The electron-derived thermal conductance can be controlled by tuning the external gate voltage because the resonant backscattering level (dangling σ-bond states around vacancies) can be shifted by the gate voltage. In contrast, thermal annealing is effective in increasing the phonon-derived thermal conductance because the quasi-bound phonon state localized around a vacancy disappears due to the annealing-induced vacancy rearrangement.

Characterization of Anisotropic Myocardial Backscatter Using Spectral Slope, Intercept and Midband Fit Parameters

The specific myocardial structural components that contribute to the observed level of backscatter from the heart and its dependence on the angle of insonification have not been completely identified: The objectives of this study were to measure the anisotropy of backscatter from myocardium using the approach first introduced by Lizzi et al. [J Acoust Soc Am 73, 1366-1373 (1983)] and to use the extracted spectral parameters (spectral slope, intercept and midband fit) to characterize changes in the apparent scatterer size, spatial concentration and acoustic impedance properties as functions of the angle of insonification. Backscatter measurements were performed in vitro on eight cylindrical formalin-fixed lamb myocardial specimens using a 5 MHz focused transducer. The backscattered spectral data as a function of angle of insonification relative to the myocardial fiber direction were analyzed over the frequency range of 4 to 6 MHz. The spectral parameters describing features of backscatter were determined by applying a linear fit to attenuation-compensated normalized spectra. Results show that values of the spectral slope do not exhibit a significant dependence on the angle of insonification within uncertainties; however, the zero-frequency intercept showed clear anisotropy and was found to be a maximum for insonification perpendicular to the predominant myofiber orientation and a minimum for parallel insonification. A comparison of midband fit values at 5 MHz with attenuation-compensated integrated backscatter values showed excellent agreement for all angles of insonification. These data suggest that measurements of spectral slope, intercept, and midband fit can provide insights regarding aspects of tissue microstructure underlying the observed anisotropy of myocardial scattering properties. Measurements of the slope parameter suggest a very modest change in effective scatterer size with angle of insonification. However, the observed anisotropy in intercept and midband fit and apparent absence of anisotropy in the spectral slope suggests an angle of insonification dependence of acoustic concentration, the combination of effective spatial scatterer concentration and acoustic impedance properties, without a significant contribution from changes in effective scatterer size.

Characterization of 1050-nm Pumped $S$-Band TDFA With Different Dopant Concentrations by Coherent Optical Frequency-Domain Reflectometry

For thulium-doped fiber amplifier (TDFA) design, knowledge of the gain distribution within the active fiber is of great value. For the first time, the distributed gain along highly thulium-doped fibers was measured with high-resolution reflectometry. The technique of coherent optical frequency-domain reflectometry is a nondestructive and noninvasive method well matched to this task due to its dynamic range, spatial resolution, and measurement range. Using thulium-doped fibers with different Tm3+-dopant concentrations, we show precise measurements of Rayleigh backscattering levels for obtaining the optimum gain-length ratio for S-band TDFA pumped by 1050-nm laser diodes

Signal Separation in Ultrasonic Non-Destructive Testing

In ultrasonic non-destructive testing the signals characterizing the material structure are commonly evaluated. The sensitivity and resolution of ultrasonic systems is limited by the backscattering and electronic noise level commonly contained in the acquired ultrasonic signals. For this reason, it is very important to use appropriate advanced signal processing methods for noise reduction and signal separation. This paper compares algorithms used for efficient noise reduction in ultrasonic signals in A-scan. Algorithms based on the discrete wavelet transform and the Wiener filter are considered. Part of this paper analyses and applies blind source separation, which has never been used in practical ultrasonic non-destructive testing. All proposed methods are evaluated on both simulated and acquired ultrasonic signals.

Impact of structural support on vector sensor acoustic performance

Vector sensors hold great promise for the exploitation of undersea acoustics by providing the ability to measure the acoustic intensity. Current sensor developments can measure the acoustic acceleration in three dimensions as well as the pressure, which when combined through a cross‐correlation produces the acoustic intensity field surrounding the sensor. Mathematical studies indicate that a gain of 4.6 dB is achievable by beamforming the sensor’s three cardioid outputs with the pressure sensor’s omnidirectional response. In these studies, the mechanics of physically retaining the sensor in position is not considered, but is necessary to allow the sensor to freely sense particle velocity/acceleration and not shadow the sensor to the surrounding pressure field. A set of PVC frames was constructed to hold an individual sensor, which was then combined to form an array of sensors for use in a long‐term shallow water acoustic field intensity study. These frames are modeled to determine the level of forward and backscatter caused by the flooded PVC pipes and the possible impact to the theoretical patterns. The physical structures are then calibrated in a controlled measurement facility to determine if the accelerometers move freely in all three dimensions to generate the cardioid patterns necessary to achieve the gains predicted by intensity models over similar pressure sensor configurations.