Signal-to-noise ratio uniformity and stability of agar gel phantom with iron (III) oxide as relaxation modifier

Background Agar has been commonly used as one of the materials to fabricate magnetic resonance imaging phantoms in the past few decades. In this study, eleven agar gel phantoms with different iron (III) oxide (Fe2O3) masses were prepared. This study was aimed to evaluate the signal-to-noise ratio (SNR) uniformity and stability of agar gel phantoms with and without the addition of Fe2O3 at two different time points (TPs). Fe2O3 powder was used as a relaxation modifier to manipulate and produce various SNR, T1 and T2 values. These phantoms were scanned using turbo spin echo pulse sequence to produce T1- and T2-measurement images. The SNR was then computed by plotting 1, 3 and 25 regions of interest on the images using ImageJ software. The T1 and T2 relaxation equations were then fitted to the experimental results of SNR versus TR and SNR versus TE curves for the determination of saturation (SNRo), T1 and T2 values. Results The results demonstrated that the agar gel phantoms were able to maintain SNR uniformity but not SNR stability after 4 weeks of phantom preparation. The change in the water content and microstructure of the phantoms have no significant effect on T2 relaxation but on T1 relaxation. The T1 and T2 of the agar gel phantoms were minimally affected although there was a systemic increase in the content of the Fe2O3 powder. Conclusions It can be concluded that the agar gel phantoms exhibited the characteristics of SNR uniformity, but they showed instability of SNR at TP2. The Fe2O3 in powder form is not an effective relaxation modifier to reduce the T1 and T2 when it is introduced into the agar gel phantoms. Dissolved nanosized particles should be the focus of future studies.

Study of the dependence of the strength characteristics of metals on variations in the modes of manufacturing process using microstructure-sensitive acoustic parameters

The microstructure-sensitive acoustic parameters (MSA parameters) of metal of the object under control are determined using measurements of the propagation time of bulk elastic waves of the ultrasonic range by the echo-pulse method. The structural features of the metal are thus evaluated not only in the surface layer, but also throughout the entire volume. We present the results of practical application of the MSA-parameters to estimation of the deviation of the velocity ratios of longitudinal and shear waves relative to the «basic» state with known strength characteristics. A correlation of the MSA-parameters with variations in the elastic moduli of metals attributed to modification of their microstructure is discussed. The generalized values of the ratios of wave velocities for steels of the same group are used in calculations to characterize the «base» state. It is shown that when calculating the MSA-parameters for a certain kind of construction steel, it is possible to use the averaged ratios of the velocities measured for quasi-isotropic reference samples made of the same type of steel. The generalized baseline ratios of the longitudinal and shear wave velocities are determined for the samples made of carbon steel, low-alloy, and alloyed steels. We present experimental evidence of using MSA-parameters to detect microstructural changes in metal samples and accompanying changes in their strength characteristics that occur during changes in modes and conditions of welding and heat treatment. A comparative analysis of the MSA parameters with the values of the mechanical properties and parameters of the crack resistance of the metal is carried out. It was shown that the accuracy of measuring the MCA parameters provided by modern hardware significantly exceeds changes in them occurred under significant deviations of the strength characteristics. The experimental results obtained clearly indicate that the MSA-parameters can be successfully used to improve the methods of quantitative non-destructive assessment of the features of metal microstructures

Theoretical determination of the criteria for bonding quality characterization inside a multilayer by ultrasonic echo-pulse method

In this work we simulated the ultrasonic response of the aluminium/adhesive/aluminium multilayer using the theoretical reflection coefficient. This investigation is based on monitoring the evolution of the amplitude of the theoretical reflection coefficient as a function of the frequency and thickness of the aluminium layer in a first step and as a function of the frequency and thickness of the adhesive layer in a second step. Based on the mode doubling of the aluminium, we found the criteria to be met for such an ultrasonic characterisation of the bonding quality to be validated.

Quantitative imaging of sodium concentrations in soil-root systems using magnetic resonance imaging (MRI)

Aims Demonstrating the potential of MRI as a 3D, non-invasive and continuous measurement technique to map Na+ concentration distributions in soil and around roots. Methods Dissolved NaCl in soil and soil-plant systems was mapped by 3D 23Na-MRI. The lower limit of detectability in saturated and unsaturated porous media was evaluated, followed by evaporation experiments to test the quantification. Finally, Na+ enrichment around tomato roots, irrigated with saline solution under low/high transpiration rates (LT, HT), was imaged in parallel to the root system,. Results A spin echo pulse sequence allowed the quantitative mapping of the volume concentration of NaCl in sandy porous medium. Evaporation experiments showed slight enrichment in the top surface layer, plus uniform temporal enrichment in the deeper layers. In the tomato experiments, enrichment was more distinct under HT than under LT. Concentration-distance correlation curves revealed thin enrichment zones ranging a few mm around the roots. Conclusions MRI can map Na+ non-invasively in 3D at relevant concentrations for root activity. Visualizing water content, roots and Na+ on the same scale is possible, despite limitations of different scanning times and resolution. This opens a route for further quantitative investigations of salt enrichment processes in soil and soil-plant systems.

Accuracy Verification of Airborne Large-Footprint Lidar based on Terrain Features

Accuracy verification of airborne large-footprint lidar data is important for proper data application but is difficult when ground-based laser detectors are not available. Therefore, we developed a novel method for lidar accuracy verification based on the broadened echo pulse caused by signal saturation over water. When an aircraft trajectory crosses both water and land, this phenomenon and the change in elevation between land and water surfaces can be used to verify the plane and elevation accuracy of the airborne large-footprint lidar data in conjunction with a digital surface model (DSM). Due to the problem of echo pulse broadening, the center-of-gravity (COG) method was proposed to optimize the processing flow. We conducted a series of experiments on terrain features (i.e., the intersection between water and land) in Xiangxi, Hunan Province, China. Verification results show that the elevation accuracy obtained in our experiments was better than 1 m and the plane accuracy was better than 5 m, which is well within the design requirements. Although this method requires specific terrain conditions for optimum applicability, the results can lead to valuable improvements in the flexibility and quality of lidar data collection.