Human rapid acquisition with relaxation enhancement imaging at 8 T without specific absorption rate violation

A standard fast imaging sequence, rapid acquisition with relaxation enhancement (RARE), has been applied to human magnetic resonance at 8 T. RARE is known for its speed, good contrast and high RF power content. HighlyT ₂ weighted images, the hallmark of RARE imaging, were acquired from the human brain. It is demonstrated that whileT ₂ values may be reduced at 8 T, high quality RARE images could still be acquired at this field strength. Most importantly however, it is demonstrated that RARE images could be acquired without violating specific absorption rate (SAR) guidelines. Since it is well known thatT ₂ weighted images are of significant value in clinical diagnosis, the implementation of RARE at this field strength will provide ultra high field MRI (UHFMRI) with a valuable imaging protocol at this field strength without exceeding SAR limitations.     

NMR microscopy of single neurons at 500 MHZ

Previous NMR microimaging studies at 360 MHz have demonstrated a clear differentiation between the nucleus and cytoplasm in isolated single neurons. In particular, theT ₂ of the cell nucleus is 2.5 times larger than that of the cytoplasm. In order to determine the magnitude of possibleT ₂ ^* influences on these observations, images of single cells have been obtained at 500 MHz using spin-echo and line-narrowing sequences. Comparison of the images acquired by the two sequences, and of the spin-echo images at 360 and 500 MHz, imply that anyT ₂ ^* contributions are relatively small. Consequently, the measuredT ₂ differences in spin-echo imaging represent a true difference in theT ₂ relaxation in the two cellular compartments.     

A method of RF inhomogeneity correction in MR imaging

A direct postprocessing method for correcting RF inhomogeneity in MR imaging is proposed. First, two images with different flip-angles of ψ and 2ψ are obtained. Next, the spatial distribution maps of the sensitivity of the surface coil and theB ₁ field intensity are produced by employing those images. Finally, the correction of the MR image is achieved, dividing the original image by distribution maps of the coil sensitivity and theB ₁ field intensity. The method was applied to image obtained by a gradient echo sequence and the corrected image is presented.     

Effects of a small amount of H2O on negative ion mobility and ion-molecule reactions in O2 at atmospheric pressure

In this study, we have measured the negative ion mobility in O₂ at high pressures with a little amount of H₂O concentration between 15 and 17,000 ppb. After that, we carried out a Monte Carlo simulation using mobility of electrons, that of the ions obtained in the measurements, and rate coefficients of ion-molecule reactions. As a result, the mobility value 2.39 cm²/V·s of O₄¯ is obtained in ultrahigh purity O₂ of which the H₂O concentration is between 15 and 100 ppb. Moreover, the mobility decreases with the H₂O concentrations at which the ion species are considered to be O₂¯·(H₂O)_n (_n = 1, 2, 3). Then, we compared the experimental result with that of the simulation and estimated the ion mobility and rate coefficients of ion molecule reactions. Simulation results using estimated values of the ion mobility and rate coefficients agree well with measurement results.     

Dielectric properties of nanocrystalline barium zirconate titanate synthesized by glycine-nitrate autocombustion

Abstract

Dielectric properties of nanocrystalline barium zirconate titanate (Ba(Zr_xTi_1-x)O₃; BZT for x?=?0.1 and 0.3) synthesized by glycine-nitrate autocombustion method were investigated in this study. The phase formation examined by TGA-DTA, XRD, FT-IR and Raman spectroscopy confirmed that high purity single-phase BZT with perovskite structure was obtained by using glycine-to-nitrate molar ratio of 2.2:4 and calcining in air at 1100?°C for 4?h. TEM analysis showed that BZT had agglomerate particles consisted of primary spherical nanocrystals with the size of 8-11?nm. The diffuse phase transition behavior of BZT ceramics increased with increasing Zr concentration and for x?=?0.3, the Curie temperature; T_c, shifted to below room temperature. The BZT ceramics for x?=?0.1 had relatively high dielectric constant (ε), 13007, low T_c, 76?°C and comparable dielectric loss (tan δ) at T_c, 0.012 which caused by the high degree of Zr diffuseness into the perovskite structure. These results suggest that glycine-nitrate autocombustion is the effective method for preparing high quality BZT ceramics.     

A time-efficient method for combinedt 1 andt 2 measurement in magnetic resonance imaging: Evaluation for multiparameter tissue characterization

A new magnetic resonance imaging high-resolution sequence is presented that allows for the collection of all data for determination ofT ₁ and as well as for multiexponentialT ₂ analysis within one measurement cycle.Noise preprocessing is performed in order to avoid systematic errors in relaxation parameter analysis and to increase the interexperimental reproducibility of the results. ForT ₂ analysis, an optimized Marquardt algorithm is used, in combination with image processing methods for both automatic detection of voxels with partial volume effects, and for speedup of the iterative nonlinear regression steps. Determination of longitudinal relaxation time is based on a sophisticated signal intensity ratio technique that computesT ₁ as the mean of up to eight individualT ₁ values, each weighted with its relativeT ₂ decay. Relative proton density is computed using results of the evaluations of both relaxation times. Validation of the method is accomplished by comparing phantom measurements with reference data acquired with spectroscopic sequences.In vivo examples of the computed parameter images taken from a study of experimental cerebral infarcts in rats are presented.The method allows one to acquire high-resolution parameter images within a measurement time that is tolerable even in clinical routine. Furthermore, the chosen evaluation concepts guarantee a short computation time. Therefore, an on-line computation of the parameter images and, in consequence, their direct use for diagnostic purposes appears feasible.     

Study of the structure and electrical properties of PMN-PNN-PT ceramics near the morphotropic phase boundary

A series of Pb(Mg_1/3Nb_2/3)O₃-Pb(Ni_1/3Nb_2/3)-O₃-PbTiO₃ (PMN-PNN-PT) ceramics with compositions of (1–x)(0.67PMN-0.33PT)-x(0.64PNN-0.36PT) (x = 0.1–0.9) were synthesized using the columbite precursor method. The phase structures, as well as the dielectric and piezoelectric properties of the ceramics were investigated in detail. X-ray diffraction results demonstrate that all the samples possess a pure perovskite structure. It is found that the morphotropic phase boundary (MPB) region of the PMN-PNN-PT ternary system is located near the line connecting the MPBs of the PMN-PT and PNN-PT binary systems. A high value of the maximum dielectric constant (ɛ_m = 45540, at 1 kHz), together with a high value of the piezoelectric coefficient (d₃₃ = 780 pC/N), were obtained for the composition x = 0.2. The results show that a partial substitution of PNN-PT for PMN-PT can lead to improved electrical properties in this ternary system.     

Breath-hold spin-echo MR imaging for evaluation of dynamic enhancement of native and treated hepatocellular carcinoma after intravenous Gd-DTPA administration

Using a simple modification of a standard spin-echo sequence which enables acquisition of three breath-hold images in 15 s, dynamic enhancement of 30 histologically proven hepatocellular carcinomas (17 native tumors, 6 completely necrotic tumors after nonsurgical treatments, and 7 tumors with viable and necrotic portions) after intravenous injection of gadolinium-DTPA was evaluated. Native hepatocellular carcinomas and viable portions in treated nodules showed elective enhancement in images obtained 40 s after contrast injection. Contrast between these lesions and the normal liver decreased thereafter. No contrast uptake was seen in entirely necrotic nodules and necrotic portions of treated nodules. Because of the capability to demonstrate the elective arterial blood supply typical of hepatocellular carcinoma, breath-holdT ₁-weighted spin-echo sequence should replace conventionalT ₁-weighted images for the evaluation of intravenously administered gadolinium-DTPA enhancement of this tumor before and after nonsurgical treatments.     

Defects and Transport in Langasite II: Donor-doped (La<Subscript>3</Subscript>Ga<Subscript>4.75</Subscript>Nb<Subscript>0.25</Subscript>SiO<Subscript>14</Subscript>)

The electrical conductivity of Nb doped langasite (La₃Ga_4.75Nb_0.25SiO₁₄) was examined as a function of temperature and oxygen partial pressure by complex impedance spectroscopy. A pO₂-independent regime was found at high pO₂ followed by a pO₂^{− 1/6} dependent regime at low pO₂. A defect model consistent with these results was derived in which the electron density n is fixed by the density of ionized Nb donors at high pO₂ and by the generation of oxygen vacancies at low pO₂. The temperature and oxygen partial pressure dependence of the electron density was obtained independently by thermoelectric power measurements. The Nb donor ionization energy was determined to be 1.52 ± 0.06 eV, confirming Nb to be a deep donor in langasite. By combining conductivity and thermoelectric power data, an expression for the electron mobility given by μ_e = 1.1× 10^{− 2}exp( ) was obtained. After evaluating the temperature dependent conductivity data under reducing conditions, in light of the defect model, a value for the reduction enthalpy (E_r = 6.57 ± 0.24 eV) was derived.     

In vivo mouse spinal cord imaging using echo-planar imaging at 11.75 T

Object To evaluate the feasibility of mouse spinal cord MR imaging using echo-planar imaging (EPI). Materials and methods Optimized multi-shot spin-echo-EPI sequences were compared to conventional spin-echo (c-SE) at 11.75 T and used for high-spatially resolved acquisitions and relaxation-time measurements. Results Good quality images were obtained, with clear delineation of gray and white matter. Acquisition-time gain factor was up to 6 (vs. c-SE) and resolution up to 74 × 94 μm² was achieved. T ₁ and T ₂ relaxation times were reliably measured. Conclusion High-temporally and spatially resolved mouse spinal cord EPI imaging is feasible. This technique should greatly benefit to long acquisition-time experiments (diffusion imaging) and imaging of rapidly-evolving pathologies. V. Callot and G. Duhamel equally contributed to this work.     

DC–3 GHz low‐noise,flat‐gain‐response,and high‐linearity amplifier

This paper describes the design, fabrication, and testing of a DC–3 GHz ultra‐wideband low‐noise amplifier (LNA) using Avago ATF‐54143 enhanced‐mode pseudomorphic high‐electron mobility transistor. Negative feedback network is introduced to ensure unconditional stability of the LNA over the full waveband. Simulation results show that the LNA provides a gain varying between 14.872 and 14.052 dB, a noise figure (NF) of less than 2.2 dB, and voltage standing wave ratios (VSWRs) approaching 2. A high simulated output third‐order intercept point (OIP₃) of >30.2 dBm is achieved. In contrast, in 1‐dB bandwidth of DC–3 GHz, the measured gain is nominal at 13.10 dB. The obtained NF changes in a small range of 2–2.178 dB, and the measured VSWRs are no more than 1.64, which are better than obtained from simulation results. At the same time, OIP₃ at 1, 2, and 3 GHz is 30.3, 29.13, and 29.34 dBm, respectively, while the output at the 1‐dB compression point (P _1dB ) is 15.43, 14.83, and 14.33 dBm, respectively. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

1000 MW机组锅炉掺烧贫煤NOx排放的燃烧优化

国内大型燃煤电站锅炉在低负荷运行工况下NO_x排放浓度往往偏高。文中采用燃烧优化运行技术,降低某电厂1000 MW超超临界机组锅炉部分负荷运行时NO_x排放浓度。通过进行现场试验并与历史运行数据比较分析发现,锅炉运行氧量偏高和掺烧贫煤是该锅炉部分负荷运行时NO_x排放浓度偏高的主要原因。试验结果表明,采用燃烧优化技术可有效控制该锅炉低负荷时NO_x排放浓度。无论是单烧烟煤还是掺烧贫煤,在机组负荷为700MW时,采用中间4台磨(B、C、D、E磨)运行的磨组运行方式代替习惯5台磨运行方式,可实现较低的NO_x排放浓度目标和较高的锅炉效率。     

Ferroelectricity in Aurivillius-Type Structure Ceramics with n = 2 and (SrBi2Nb2O9)0.35(Bi3TiNbO9)0.65 Composition

Aurivillius-type structure compounds are good candidates for their use as high temperature piezoelectrics, due to their high ferro-paraelectric phase transition temperature. However, this characteristic correlates with a high coercive field that makes difficult the poling process, necessary to have piezoelectric activity. The electric properties, specially conductivity, limit the maximum poling field. On the other hand, piezoelectric properties are directly related to the ferroelectric remanent polarization. Thus, the study of both characteristics is towards improving the piezoelectric properties of these materials. In this work, ceramics with nominal composition (SrBi₂Nb₂O₉)_0.35(Bi₃TiNbO₉)_0.65 (T_C∼ 760^∘C), prepared by hot pressing of mechanically activated precursors, have been studied. The electrical properties (permittivity, dielectric loss factor and d.c. conductivity) as a function of frequency and temperature have been measured, up to temperatures higher than the ferro-paraelectric phase transition, and their anisotropy explained in terms of the ceramic texture. Well-saturated ferroelectric hysteresis loops at 250^∘C have been obtained, with values of P_r = 21.4 μ C/cm² and E_c = 70.4 kV/cm.     

Competitive evolutionary algorithms for building performance database of a microwave transistor

In this work, the simultaneous trade‐off relations among the noise figure F, gain G_T, input V_in, and output V_out VSWRs of a microwave transistor operated at a certain (V_DS, I_DS, f) condition are obtained fast and as accurate as the corresponding analytical results using multiobjective optimization process without any need for expertise on the microwave device, circuit, and noise. Three powerful evolutionary algorithms, cuckoo search, firefly, and differential evolution, are implemented comparatively as a study case to obtain the trade‐off relations of a typical low‐noise amplifier transistor NE3511S02 for its operation between 9 and 17 GHz at V_DS = 2 V and I_DS = 10 mA. Finally, differential evolution is found as the most successful algorithm to demonstrate the typical trade‐off relations of NE3511S02. It can be concluded that these trade‐off relations being obtained by using a signal and noise model of the transistor enable performance database covering all the (F ≥ F_min, G_T, V_in ≥ 1, V_out ≥ 1) quadruples with their (Z_S, Z_L) termination pairs using solely an evolutionary optimization process. Thus, a small signal transistor can be identified by its performance database to be used in the design optimization of high‐performance low‐noise amplifiers with the full device capacity.     

Magnetic core properties and their thermal stability in a BCC Fe-Zr-B-Cu alloy with nanoscale grain size

A mostly single bcc phase with nanoscale grain size of 10 to 20 nm has been found to form by annealing amorphous Fe-Zr-B, Fe-Hf-B and Fe-M-B-Cu (M = Ti, Zr, Hf, Nb and Ta) alloys. It has further been clarified that the newly developed nanocrystalline bcc alloys exhibit high permeability (μ_e) combined with high saturation magnetization (B_s). Subsequently, the possible application potentials of the bcc alloys were investigated. The core loss is as small as 66 mW/kg at 1 T and 50 Hz for a nanocrystalline bcc Fe₈₆Zr₇B₆Cu₁ alloy obtained by annealing for 3.6 ks at 873 K. This value is 45 and 95 percent smaller than those for amorphous Fe₈₆Si₉B₁₃ alloy and Fe-3.5 percent Si alloy, respectively, which are presently in use as core materials in electric power transformers. The frequency dependence of the core loss for the bcc alloy at 0.2 T is almost the same as that for an amorphous Co_70.5Fe_4.5Si₁₀B₁₅ alloy with zero magnetostriction. In the frequency range of 10 to 300 kHz, the core loss for the bcc alloy is slightly smaller than the Co base amorphous which has been used as core material in high-frequency transformers. Furthermore, the core losses of the nanocrystalline Fe₈₆Zr₇B₆Cu₁ alloy also were found to have high stability against thermal aging. Thus, nanocrystalline bcc Fe-Zr-B-Cu alloys with the advantages of high B_s, high μ_e, and low core loss is expected to be used as a core material in various transformers.     

Particle composition and heat capacity of high‐temperature SF6 present at constant volume: Discussion on formula expressing relationship between constant‐pressure and constant‐volume heat capacities

Until now, the high‐temperature properties of SF₆ have been derived as a function of T for a given constant pressure P. This was based on the adoption of T and P as gas state parameters. In contrast, this paper adopts T and the gas volume V as the gas state parameters and then evaluates the particle composition and gas pressure for high‐temperature SF₆ present at a constant volume state. This evaluation is achieved by the minimization of Helmholtz free energy of the high‐temperature SF₆. A further derivation for the SF₆ gas at constant volume is performed to reveal the temperature dependence of the molar heat capacity C_Vm [J/(mol·K)] and the specific heat C_Vg [J/(kg·K)]. Use of the obtained C_Vm enabled us to discuss whether the formula C_Pm−C_Vm=R_m holds true for the high‐temperature SF₆ or not, where C_Pm and R_m are the molar heat capacity at constant pressure and the universal gas constant, respectively. Similar discussion is also performed on the formula indicating the relation between C_Pg and C_Vg, where C_Pg is the specific heat at constant pressure. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Magnetic resonance imaging of bovine ovaries in vitro

A sample of 20 bovine ovaries were imaged in vitro using nuclear magnetic resonance (NMR) techniques to determine the visibility of various physiologic structures. In particular, the possibility of using NMR imaging to differentiate atretic follicles from physiologically selected and ovulatory follicles was examined. Five of the 20 ovaries were preserved in formalin, whereas the remaining 15 were preserved in a saline solution and imaged within 18 hours of death. Images weighted by T₁ and T₂ proton spin relaxation rates were obtained along with some three-dimensional (3-D) data sets acquired via a fast imaging with steady-state precession technique. Physiologically different structures were easily identified in the images from their morphology, especially in the 3-D images. Weighting by T₁ and T₂ was able to separate structures in the fresh ovaries in the following manner. Atretic and cohort follicles appear dark in T₁-weighted images and bright in T₂-weighted images. Ovulatory follicles appear bright in both T₁-and T₂-weighted images, whereas prephysiologic selection follicles present an intermediate brightness in T₁-weighted images and appear dark in T₂-weighted images. The corpus luteum appears bright in T₁-weighted images and dark in T₂-weighted images, whereas cysts in the corpus luteum appear dark in T₁-weighted images and bright in T₂-weighted images. The varying brightness of the follicles at different stages of development is hypothesized to be related to different hormone and protein concentrations in the follicular fluid. For example, it is known that physiologically selected preovulatory follicles contain high concentrations of estrogens in a viscous follicular fluid. The increased viscosity may occur only when the follicle fluid contains high concentrations of estrogen and contributes to bright T₁-weighted images. The possibility of using nuclear relaxation-weighted NMR imaging for the study of follicular dynamics and other ovarian biology therefore shows great promise.     

A comparison of phase imaging and quantitative susceptibility mapping in the imaging of multiple sclerosis lesions at ultrahigh field

Objective

The aim of this study was to compare the use of high-resolution phase and QSM images acquired at ultra-high field in the investigation of multiple sclerosis (MS) lesions with peripheral rings, and to discuss their usefulness for drawing inferences about underlying tissue composition.

Materials and methods

Thirty-nine Subjects were scanned at 7 T, using 3D T ₂*-weighted and T ₁-weighted sequences. Phase images were then unwrapped and filtered, and quantitative susceptibility maps were generated using a thresholded k-space division method. Lesions were compared visually and using a 1D profiling algorithm.

Results

Lesions displaying peripheral rings in the phase images were identified in 10 of the 39 subjects. Dipolar projections were apparent in the phase images outside of the extent of several of these lesions; however, QSM images showed peripheral rings without such projections. These projections appeared ring-like in a small number of phase images where no ring was observed in QSM. 1D profiles of six well-isolated example lesions showed that QSM contrast corresponds more closely to the magnitude images than phase contrast.

Conclusions

Phase images contain dipolar projections, which confounds their use in the investigation of tissue composition in MS lesions. Quantitative susceptibility maps correct these projections, providing insight into the composition of MS lesions showing peripheral rings.

     

Low temperature sintering of (Ba0.85Ca0.15) (Ti0.90Zr0.10)O3 lead-free piezoceramic with the additive of MnO2

Lead-free (Ba_0.85Ca_0.15) (Ti_0.90Zr_0.10)O₃ (15/10 BCZT) piezoelectric ceramics were prepared by a standard solid solution and sintered at different temperature of 1300 °C and 1500 °C at a time. The 15/10BCZT piezoceramics were prepared at 1300 °C sintering temperature by doping different amount of MnO₂.The ceramics show a phase transition from a freoelectric tetragonal phase to a rhombohedral and tetragonal ferroelctric phase and to a single rhombohedral phase with increasing MnO₂ content. The addition of MnO₂ significantly improves the sinterbility of the 15/10BCZT piezoceramics, and reducing the sintering temperature from 1500 °C to 1300 °C by 200 °C but showing comparable piezoelectric properties. With 0.4 mol% of the dopant, ～96.5% of the theoretical density of the ceramics was achieved with excellent piezoelectric coefficient d₃₃ ~ 534pC/N, which is nearly equal to the value obtained from the ceramics sintered at 1500 °C which has a piezoelectric coefficient d₃₃ ~ 570pC/N, high density (~ 5.59 g/cm³), maximum remnant polarization (P_r = 24 μC/cm²), relatively large grain size (10.4 μm) and the least coercieve field (E_c = 0.42 kV/mm). However, a high concentration of MnO₂ deterioated the properties of the ceramics because of increasing of oxygen vacancies and associated defects. The results indicate that the BCTZ-y mol% MnO₂ ceramics are one of the promising lead-free piezoelectric candidates for high temperature applications.

     

Influence of Annealing Temperature on Structural,Morphological and NH3 Sensing Properties of Nanostructured WO3 Porous Films

The tungsten trioxide (WO₃) precursor was prepared by sol-gel method with tungsten powder as the raw material, and the WO₃ gas sensing films were obtained by a dip coating method and annealing precursor in air. X-ray diffraction (XRD) spectra indicate that with increasing annealing temperature the triclinic structure of as-prepared sample was transformed into monoclinic or orthorhombic phase. The images of scanning electron microscopy (SEM) exhibit that the WO₃ grain sizes increase from less than 100 nm to several micrometers with increasing annealing temperature. The influences of applied frequency, annealing and operating temperature on NH₃ gas sensing properties of the nanostructured WO₃ porous films were investigated. The results indicate that the gas sensing film annealed at 500°C express high sensitivity, fast response and recovery speed to NH₃ at operating temperature 250°C.