Intensity Of Echo Signal Research Articles

Low-Level Jets in the Moscow Region in Summer and Winter Observed with a Sodar Network

We evaluate the statistical properties of low-level jets (LLJs) observed by means of a network of Doppler sodars in the Moscow region, Russia. Continuous long-term measurements of the echo-signal intensity and wind-velocity profiles were carried out in July 2005 and in 2008–2010 synchronously in the centre of Moscow and at a rural site. The summertime nocturnal LLJs have a very clear diurnal cycle and exhibit features predicted by the Blackadar mechanism. In contrast, the long-lasting wintertime jets do not have any clear diurnal variability. The urban environment strongly influences LLJs in both seasons: above the city LLJs are higher, weaker and observed more rarely than at the rural site. In very cold periods (air temperature below −8°C) no LLJs were observed over the city, instead convection emerged in the urban boundary layer. The results are based on observations made in July 2005, January and December 2009, and January 2011.

NMR studies of the gelation mechanism and molecular dynamics in agar solutions

Changes in the molecular mobility of agar were measured by pulsed-field-gradient stimulated echo (PFG-STE) 1H NMR at various temperatures in order to elucidate the mechanism of gelation in solutions. The echo signal intensity of agar decreased steeply and the diffusion coefficient D of agar increased near the sol-to-gel transition temperature T s–g, and D decreased with further cooling. These results suggested that the polysaccharide chains in agar aggregated in bundles to form a network at around T s–g. High molecular weight chains aggregated preferentially in agar, with the soluble, non-aggregated agar (“solute agar”) left in the network forming loose aggregates upon further cooling. Evidence for this behavior was obtained from GPC measurements on the solute agar squeezed from the gel. These loose aggregates readily disassociated on reheating, whereas the aggregated bundles were quite thermally stable, which corresponded well with the thermal stability of the gel strength. The changes in the restrictions on molecular mobility in these solutions were evaluated from measurements of D of a dendrimer added as a probe molecule, which was sensitive to the dilution of the solute agar accompanying gelation. The hydrodynamic shielding length ξ, which was considered to represent the hydrodynamic mesh size created by the solute agar, was calculated from D of the dendrimer, shedding light on the changes in the microscopic environment during gelation.

Measuring Sediment Thickness in Borehole by Ultrasonic Based on Channel Estimation

Sediment on the bottom of borehole forms a major part which is often responsible for reducing the bearing capacity of pile. The normal method of measuring sediment thickness by ultrasonic signal is to measure the sound time and intensity of echo signal. This paper presents a novel measurement method by estimating the ultrasonic channel. Wiener filter is applied to estimate the ultrasonic optimal channel under minimum mean square error criteria. Experiments of estimating channel based on Wiener filter have been conducted with given signals and actual ultrasonic detection echo. The influence of noise in the signal has been discussed. The results show that, during signals high SNR, the estimated channel is corresponding to the sharp changes in the actual signal and can be used to determine the sediment thickness.

A variable echo‐number method for estimating in MRI‐based polymer gel dosimetry

Spin-spin relaxation rate R2 is commonly used to quantify absorbed dose for magnetic resonance imaging (MRI)-based polymer gel dosimetry. R2 is estimated by applying a parameter fitting algorithm to a train of spin-echo signals. However, a careless application of a large number of echoes can result in anomalous R2 values because the echo signal intensity decreases to the background signal offset level for a long echo time. In this article, the authors proposed and evaluated a variable echo-number (VAREC) method to remedy the problem. The VAREC algorithm uses only echo signals, whose intensities are greater than a preset threshold. Here, the threshold is defined as the standard deviation of Gaussian noise times a multiplier alpha. The authors implemented three R2 estimation methods in an in-house program: The nonlinear least-squares algorithm (NLLS), the VAREC method, and the maximum likelihood estimator with the Rician signal intensity distribution (MLE_R). Those methods were used to estimate the R2 values of test phantoms with known R2 values and BANG3-type polymer gels, which were irradiated to 12 different doses ranging from 0 to 50 Gy. The R2 values were measured by using a 32-echo CPMG pulse sequence on 3 T MRI scanners. The R2 values of the VAREC method were compared with those of NLLS and MLE_R. The R2 values of the NLLS method incorrectly decreased to the zero-dose level for doses greater than 10 Gy. The R2 values of the VAREC method with alpha=2 agreed with those of MLE_R within the measurement uncertainty. The uncertainties of the R2 values were the smallest for alpha=2 or 3 among various alpha values. The VAREC algorithm is simple, fast, and robust for the R2 estimation. The authors recommend this method with alpha=2 or 3 for R2 estimation using multispin echo MRI protocols.

Assessment of tissue perfusion by contrast-enhanced ultrasound

Contrast-enhanced ultrasound (CEUS) with microbubble contrast agents is a new imaging technique for quantifying tissue perfusion. CEUS presents several advantages over other imaging techniques in assessing tissue perfusion, including the use of microbubbles as blood-pool agents, portability, availability and absence of exposure to radiation or nuclear tracers. Dedicated software packages are necessary to quantify the echo-signal intensity and allow the calculation of the degree of tissue contrast enhancement based on the accurate distinction between microbubble backscatter signals and native tissue background. The measurement of organ transit time after microbubble injection and the analysis of tissue reperfusion kinetics represent the two fundamental methods for the assessment of tissue perfusion by CEUS. Transit time measurement has been shown to be feasible and has started to become accepted as a clinical tool, especially in the liver. The loudness of audio signals from spectral Doppler analysis is used to generate time-intensity curves to follow the wash-in and wash-out of the microbubble bolus. Tissue perfusion may be quantified also by analysing the replenishment kinetics of the volume of microbubbles after their destruction in the imaged slice. This allows to obtain semiquantitative parameters related to local tissue perfusion, especially in the heart, brain, and kidneys.

Range accuracy limitation of pulse ranging systems based on Geiger mode single-photon detectors

Geiger mode single-photon detectors have been used in pulse ranging system and three-dimensional imaging systems due to high sensitivity and easy integration. The ranging accuracy and precision is influenced by many factors. Based on statistical theory, five main factors are discussed in this article, namely, echo signal intensity, pulse width, detector quantum efficiency, target position, and background noise. An analytical relationship among the ranging accuracy, precision, and these factors is obtained for a Q-switched laser pulse. Through this relationship, it is shown that the echo signal intensity and pulse width are more important than other factors and higher echo signal intensity and narrower pulse width can result in better accuracy and precision.

Afternoon Pc5 geomagnetic pulsations on the Earth’s surface and in the ionosphere (STARE radars)

Two cases when Pc5 geomagnetic pulsations were registered at the IMAGE Scandinavian network of stations and with STARE radars in the afternoon sector (1700–1800 MLT) during the recovery phase of the moderate magnetic storm are analyzed in detail. Using the ground-based observations, it has been indicated that classical quasimonochromatic resonance Pc5 pulsations were observed in the first case (on October 12, 1999; Kp = 5); in this case the maximal amplitude of the spectral maximum at a frequency of 2.5 mHz was registered at Φ ∼ 65°. Two maximums were observed in the spectrum in the second case (on October 13, 1999; Kp = 4): ∼2.5 mHz (the same maximum) and 2.9 mHz; in this case the maximal oscillation amplitude (2.5 mHz) shifted to Φ > 67°. These results were compared with the echo signal intensity simultaneously registered with the STARE Finland radar on a beam oriented along the 105° geomagnetic meridian. The spatial-temporal maps of the Pc5 pulsation amplitude latitudinal distribution (“keograms”), constructed based on the radar measurements in the wide range of geomagnetic latitudes (63°–70°) where the resolution was substantially higher than that of the ground-based observations, made it possible to detect two regions spaced in latitude (Φ ∼ 65° and Φ ∼ 67°–68°) with the simultaneous excitation of oscillations (double resonance?), between which the plasmapause projection was supposedly located.

Ultrasonic diagnostic equipment and image processing apparatus

After the establishment of the saturation state of a contrast medium which has flowed into a subject for scanning inside a patient given the contrast medium, scan is performed under a high acoustic pressure adapted to break the bubbles of the contrast medium, so as to refresh the section for the scanning, and to acquire the maximum value of echo signal intensities. Subsequently, scans by ultrasounds under a low acoustic pressure or a medium acoustic pressure which does not break the contrast medium are carried out a plurality of times at different timings, thereby to execute a scan sequence for acquiring in-vivo information necessary for a TIC analysis. Data obtained by the scans are analyzed in a blood-flow-index estimation unit, and are displayed in a predetermined scheme.

Assessment of a New Mathematical Model for the Computation of Numerical Parameters Related to Renal Cortical Blood Flow and Fractional Blood Volume by Contrast-Enhanced Ultrasound

We analyzed the value of a new mathematical model for the quantification of renal cortical blood flow and fractional blood volume by contrast-enhanced ultrasound after the injection of sulfur hexafluoride–filled microbubbles. A vessel-mimicking phantom experiment was preliminarily performed which showed that the effect of microbubble diffusion is negligible compared with the effect of liquid drag. Twelve healthy volunteers (7 male, 5 female; 27 to 48 years [ n = 6; group 1], and 61 to 80 years [ n = 6; group 2], respectively), with normal renal and cardiac function and not undergoing any pharmacologic treatment, were examined. In each volunteer, both kidneys were scanned after intravenous injection of sulfur hexafluoride–filled microbubbles at a slow rate (4.8 mL at a flow of 4.0 mL/min), and the refill kinetics of the renal cortex after microbubble destruction was evaluated by echo-signal intensity quantification. The progressive replenishment of the renal vessels was approximated both by standard negative exponential function and by the piecewise linear function resulting from our mathematical model. A better dataset approximation was provided by piecewise linear versus standard negative exponential function (overall mean square error: 0.44 vs. 0.51; p < 0.05, Wilcoxon test). The piecewise linear function provided a curve composed of four linear tracts ( n = 3 volunteers; 2 from group 1 and 1 from group 2), three linear tracts ( n = 6 volunteers; 3 from group 1 and 3 from group 2) or two linear tracts ( n = 3 volunteers; 1 from group 1 and 2 from group 2). The piecewise linear function versus standard negative exponential function improved data approximation for the computation of numerical values related to renal cortical blood flow velocity and fractional blood volume. (E-mail: quaia@univ.trieste.it)

Quantitative estimate of the role of temperature gradients in sodar echo signal formation

We estimate the intensity of a sodar echo signal caused by thin layer with sharp gradient of a temperature. This intensity under some circumstances may exceed the intensity of backscattering from small-scale turbulent inhomogeneities by orders of magnitude.

Motion-Compensated Frame-Accumulating Method to Improve Quality of Carotid Artery Images

The motion-compensated frame-accumulating method (MCFAM) was carried out to improve B-mode image quality for plaque diagnosis. The effect of MCFAM on the imaging of the carotid intima, one of the potential predictors of plaque growth, was examined using the carotid of a healthy volunteer. MCFAM was found to be effective in imaging the carotid intima clearly as a contiguous object, although conventional imaging failed to visualize the entire intima. Quantitatively, the deviation of the echo signal intensity along the carotid intima, which corresponded to the discontinuity of the intima image, was 31% in the MCFAM image, 48% smaller than that in the conventional image. The deviation became lower with an increase in the number of accumulating frames in MCFAM, and was almost constant when more than 16 frames were accumulated. Because of the relatively small number of frames required, MCFAM was suggested to have the potential to contribute to quantitative plaque diagnosis by enabling accurate measurements of the carotid intima.

Little Leaguer’s shoulder (proximal humeral epiphysiolysis): MRI findings in four boys

Shoulder pain is a common problem among adolescent athletes. A possible cause of such pain that can be diagnosed on MRI is a stress injury to the proximal humerus known as Little Leaguer's shoulder (proximal humeral epiphysiolysis). Our objective was to describe the MRI appearance of Little Leaguer's shoulder. Four patients (all boys; age range 11-15 years; median 13 years) with clinical, plain radiographic, and MR imaging findings of Little Leaguer's shoulder were studied retrospectively. MRI demonstrated focal physeal widening in all four boys with extension of physeal signal intensity into the metaphysis on T1-weighted and gradient echo coronal and sagittal sequences. T2-weighted sequences were of limited use in demonstrating the physeal widening, which is critical to the diagnosis. Abnormal high T2-signal intensity was seen in the metaphysis adjacent to the focal physeal widening in all the boys. Focal extension of normal physeal T1-weighted and gradient echo signal intensity into the adjacent metaphysis is a sign of stress injury in the proximal humeral physis (Little Leaguer's shoulder). Children should suspend the offending sport to allow healing.

Microbubble ultrasound contrast agents: an update

Microbubble contrast agents for ultrasound (US) have gained increasing interest in recent years, and contrast-enhanced US (CEUS) is a rapidly evolving field with applications now extending far beyond the initial improvements achieved in Doppler US. This has been achieved as a result of the safe profile and the increased stability of microbubbles persisting in the bloodstream for several minutes, and also by the availability of specialized contrast-specific US techniques, which allow a definite improvement in the contrast resolution and suppression of signal from stationary tissues. CEUS with low transmit power allows real-time scanning with the possibility of prolonged organ insonation. Several reports have described the effectiveness of microbubble contrast agents in many clinical applications and particularly in the liver, spleen, and kidneys. CEUS allows the assessment of the macrovasculature and microvasculature in different parenchymas, the identification and characterization of hepatic and splenic lesions, the depiction of septal enhancement in cystic renal masses, and the quantification of organ perfusion by the quantitative analysis of the echo-signal intensity. Other fields of application include the assessment of abdominal organs after traumas and the assessment of vesico-ureteral reflux in children. Finally, tumor-targeted microbubbles make possible the depiction of specific biologic processes.

Dolphins’ echolocation strategy of target identification: Is it determined by the peripheral auditory encoding?

It is well known that the auditory system of dolphins is capable of analyzing the fine frequency—time structure of short high-frequency echo signals. This can be explained by the burst principle, according to which the auditory peripheral encoding of signals is determined by the collective effect of a multitude of synchronously excited auditory nerve fibers. Encoding is efficient when the sensitivity of the majority of the fibers corresponds (is close) to the level of the synaptic potential evoked by the stimulus. Under the effect of long signals, such a correspondence is achieved as a result of auditory adaptation, which adjusts the sensitivity of the fibers to the synaptic potential level. However, dolphins identify a target by analyzing a single short echo signal, but, in the course of echolocation, they vary the intensity of the probing pulse over wide limits. In this paper, a model of the high-frequency auditory periphery is used to test the hypothesis that the intensity variation is an adaptive mechanism serving for the adjustment of the intensity of echo signals to the fiber sensitivity, which is formed under the effect of ambient noise. It is found that a necessary condition for the realization of the burst principle is the presence of the differentiating properties inherent in the response of the multitude of auditory nerve fibers. The identification of short signals is interpreted in terms of a model that includes a model of the auditory periphery and units serving for the minimization of signal description and for making decisions. A model algorithm of small-target identification by echolocation, which realizes the object identification strategy used by dolphins, is discussed.

A241 マルチNMRセンサーによる水電解運転時のPEM内含水量の分布計測(超音波・電磁波による熱流体計測2)

A distribution-measurement system with 8 channel transceivers and multi-surface-coils of 1.3mm outside diameter for monitoring water content distribution in polymer electrolyte membrane (PEM) was developed. Using the CPMG method, water content in PEM can be obtained from echo-signal intensity and T_2(CPMG) relaxation time. MEA (Membrane Electrode Assembly) was put in the cell controlled at the cell temperature of 75℃ and the vapor concentration of 0.14 kg/m^3 in N_2 gas. Time-dependence changes of echo-signal intensity of MEA under water electrolysis condition were obtained by the multi-surface-coils on the anode and cathode electrodes.

NMR Study on Ferroelectric (CH3)2NH2H2AsO4

The dimethylammonium dihydrogen arsenate (CH3)2NH2H2AsO4 (DMADA), which belongs to KDP-type crystals, undergoes a ferroelectric phase transition of second order at 274.5K (1⁄4 Tc). The phase transition is characterized by the symmetry change from the monoclinic-space group P21=n to Pn. 1) It was also reported that this crystal shows the drastic isotope effect on the phase transition temperature by deuteration. Moreover, the critical slowing-down phenomenon of polarization has been observed near Tc. 2) These facts suggest that the phase transition at 274.5K is of the order– disorder type and that the hydrogen plays an important role in the phase transition of DMADA. In addition to these properties, this crystal shows the unique and interesting features that spontaneous polarization increases slowly with decreasing temperature below Tc and is not saturated even at 77K. On the other hand, the spontaneous polarization is saturated at a temperature T 1⁄4 Tc 10K in the KH2AsO4 crystal. The replacement of the K ion of KDP family with the dimethylammonium ion will lead to such a tempeature dependence of spontaneous polarization in DMADA. Therefore, investigations on not only hydrogen dynamics at the order–disorder phase transition of 274.5K but also the motion of dimethylammonium ion will be helpful for generalizing the ferroelectricity and ferroelectric phase transition of KDP-type crystals. Recently, we have carried out H-NMR measurements for DMADA. In the present paper, we report the dynamics of hydrogen from the results of the spin–lattice relaxation and the NMR line measurements in DMADA. The DMADA single crystals were grown by slow evaporation method at 303K from an aqueous solution containing (CH3)2NH2 and H3AsO4 in equimolar ratio. The measurement of the H spin–lattice relaxation time T1 was performed using pulse spectrometer (Thamway Prot1002MR) with the frequency of 10.5MHz. The spin–lattice relaxation time was obtained from the recovery of the intensity of the spin echo signal following the saturation comb pulses. The H-NMR lines were observed with the NMR spectrometer by the Q meter detection method. In the NMR measurement, the powder specimens were used. The temperature dependence of H spin–lattice relaxation ratio at 10.5MHz is shown in Fig. 1. The spin–lattice relaxation rate T 1 1 takes a maximum at about 107K, and a sharp peak at 275K (see the inset of Fig. 1). The anomaly of T 1 1 near 275K is characterized by a very sharp peak. This crystal undergoes the phase transition of the order–disorder type at 274.5 K. Therefore, this anomaly of T 1 1 accompanies the phase transition observed at 274.5K. Moreover, we note that T 1 1 shows the change from 83.3 s to 0.285 s below room temperature. In the case that the rotation of methyl group exists, T 1 1 is given by

Three-dimensional imaging of pore water diffusion and motion in porous media by nuclear magnetic resonance imaging

We report on the use of a pulsed gradient spin-echo imaging sequence for the three-dimensional (3D) imaging of water transport properties in two porous media: 2mm glass-beads and 0.15mm quartz-sand mixed with 2mm glass-beads. In contrast to tracer methods, which monitor the tracer motion by its effect on the signal relaxation of 1H, this sequence measures the echo signal intensity I0 without and I with applied diffusion gradient, respectively. For the wide-pore glass-bead system, the intensity loss is controlled by nearly free self-diffusion in the pores. A mean apparent diffusion coefficient is calculated from the ratio ln(I0/I) as 〈Dloc〉=1.9×10−9m2s−1, which is slightly lower than that of free water (D=2.3×10−9m2s−1). Increasing the mean pore flow velocity from 0 to 0.14mms−1 results in a linear increase of 〈Dloc〉 to 2.3×10−9m2s−1, caused by mechanical dispersion. The spatial distribution is of the log-normal type, where the width increases with increasing pore velocity. Correlation lengths are also calculated.For the fine porous medium, frequent contacts of the water molecules with the pore boundaries lead to a significant decrease of I0 by increased T2 relaxation. The resulting ratio of the signal intensities ln(I0/I) is then smaller than expected for pure diffusion, which is caused by the restricted diffusion in the fine pore system. The spatial distribution (normal) is broader than for the glass-bead system and the mean local apparent diffusion coefficient is calculated as 1×10−9m2s−1, a dependence on the pore flow velocity could not be detected.For the glass-bead system, the 3D image clearly shows regions of increased dispersivity (50% greater than the 〈Dloc〉), caused by packing errors, leading to preferential flow. This macroscopic effect on the column scale is quantified by a numerical simulation of tracer transport, based on the 3D diffusion coefficient field, assuming a linear relation to local velocities. From this simulation, the effective dispersion coefficient is obtained for the column scale (Deff=130×10−9m2s−1), which is comparable to that obtained from classical break-through curves with tracer substances.

Phonon echo in hydrogen-containing metals

The phonon echo due to the tunneling of the hydrogen atom between two equilibrium positions in hydrogen-containing niobium NbOxHy is investigated. The time dependence of the intensity and shape of the two-pulse echo signal is obtained.

Measurement of the relaxation rate of the magnetization in Mn12O12-acetate using proton NMR echo

We present a novel method to measure the relaxation rate W of the magnetization of Mn 12O (12)-acetate (Mn12) magnetic molecular cluster in its S = 10 ground state at low T. It is based on the observation of an exponential growth in time of the proton NMR signal during the thermal equilibration of the magnetization of the molecules. We can explain the novel effect with a simple model which relates the intensity of the proton echo signal to the microscopic reversal of the magnetization of each individual Mn12 molecule during the equilibration process. The method should find wide application in the study of magnetic molecular clusters in off-equilibrium conditions.

A Two-Regime Model For The Probability Density Function Of The Temperature Structure Parameter In The Convective Boundary Layer

The experimentally observed probability distribution of the acoustic echo-signal intensity associated with the temperature structure parameter CT2 was found to be markedly non-lognormal in the convective boundary layer. A two-regime model of thermal turbulence is suggested that combines a small-scale turbulence description with the concept of coherent structures. The probability density function of the logarithm of the temperature structure parameter CT2 is assumed to be approximated by a combination of two normal distributions taken with corresponding weights. It can be interpreted as the existence of two regimes of thermal turbulence, namely, light background turbulence and strong turbulence within convective plumes. This decomposition of the probability density function into ‘plume’ and ‘background’ parts provides an objective procedure for separating the statistics of these two regimes as well as to determine the probability of convective plume occurrence. It is shown that the conventionally measured overall mean CT2, averaged over a long enough time interval, is determined mainly by the probability of plume occurrence, while the mean CT2 value within plumes changes slightly. The decrease of the total mean CT2 with height is caused mainly by the decrease of the probability of the plume occurrence with height.