Spin-lattice relaxation and magnetization transfer in intracranial tumors in vivo: Effects of Gd-DTPA on relaxation parameters

Spin-lattice relaxation time T₁ and relaxation parameters in magnetization transfer (MT) imaging were measured in 11 intracranial tumors before and after injection of Gd-DTPA at 0.1 T by using the inversion recovery method and the saturation transfer technique, respectively. Preinjection T₁ relaxation times of the tumors were longer than those of white matter, but after Gd-enhancement the relaxation times of most tumors were in the same range as those of white matter. Gd-DTPA shortened the apparent relaxation time in the presence of off-resonance saturation pulse (T_1α) due to marked shortening of the relaxation time of mobile water (T_1w). Gd-DTPA decreased the magnetization transfer contrast (MTC) but did not influence on the magnetization transfer rate (R_wm). The parameters MTC and R_wm differed clearly between Gd-enhanced tumors and normal brain, whereas the relaxation time T_1α was in many Gd-enhanced tumors in the same range as in normal brain.     

Effect of fasting and food intake on magnetization transfer of human liver tissue

Magnetization transfer (MT) technique is a promising method in differential diagnosis of diseases in parenchymal tissues. Basic knowledge about circumstances and elementary factors that influence MT and its parameters is still insufficient, however. Having a meal before the magnetic resonance (MR) examination could change liver MT parameters compared to fasting state through alteration in liver perfusion, blood flow, and content of portal blood (proteins and other derivates from a meal). If MT parameters can be altered by a meal, then MR liver studies should always be performed after fasting. Before MRI examinations we examined three healthy volunteers after a high-fat meal with Doppler ultrasound technique to find out duration and magnitude of changes in portal blood flow. Duration of ≥50% increased peak-flow value compared to fasting state in portal vein was >90 min, which is enough for our MR examination. With a low-field 0.1-T MR imager we examined 10 healthy volunteers after a short (range from 3 h 45 min to 17 h 30 min) fast and also immediately after a high-fat meal. Magnetization transfer parameters, magnetization transfer ratio (MTR) and magnetization transfer rate R_wm of liver tissue were determined. MTR changed significantly (Student paired two-tailed t-test, p = .0044) after a meal, but R_wm did not (p = .0952). We recommend a 4 h fast before MR examination that aims to determine the MTR of liver tissue.     

Magnetic anisotropy,magnetostriction and intermediate range order in Co-P alloys

Coercivity, magnetostriction and saturation field as a measure of magnetic ansitropy energy have been investigated in Co_100-xP_x with 5 ? x ? 26. According to their magnetization curves and coercivities crystalline alloys (5 ? x ? 11) contain hcp-inclusions whereas amorphous material (12 ? x ? 26) is magnetically soft. The saturation magnetization is mainly determined by the nearest neighbour shell but magnetostriction is also correlated with the further environment of the cobalt atoms. The abrupt breakdown of the value |λ_s| of the saturation magnetostriction with increasing phosphorus content of the crystalline alloys points to a growing structural disorder. λ_s of the amorphous material depends on the saturation magnetization alone (λ_s ≈ σ₀²) which decreases with increasing phosphorus content. The small value of λ_s suggests that angular correlations do not exceed the second coordination shell.     

MRI phantom for tissue simulation with respect to diffusion coefficient and kurtosis - Validation with injection of liposomal theranostics

This study presents gelatine-based and agar-based phantoms with an addition of glycerol, safflower oil, silicone oil and cellulose microcrystalline with a potential to cover the entire range of tissue diffusion coefficients and kurtosis values. Forty types of phantoms were prepared and examined for NMR relaxation times T₁ and T₂ and diffusional metrics D, K and ADC. Wide ranges of values of D (0.0003–0.0031 mm²s⁻¹), K (0.00–7.24) and ADC (0.0002–0.0031 mm²s⁻¹) were observed. Two of the phantoms closely mimic muscle and cortical gray matter with respect to water diffusion parameters. Although many of the presented phantoms display both D and K values within the range of human tissues, they match different tissues with respect to D and K. The imaging results for the gray matter simulating phantom injected with the liposomal solution, bear a resemblance to the particle size effect described in the literature. The phantoms presented in this work are simple in preparation and affordable tissue-simulating materials to be used primarily in development of diffusion kurtosis-based MRI methods and possibly in a preliminary assessment of MRI contrast agents. Further adjustments of the chemical compositions could potentially lead to development of new types of phantoms mimicking diffusional properties of more kinds of soft tissues.     

(Ni, Zn, Sn) Ru and (Ni, Sn) Sn substituted barium ferrite prepared by mechanical alloying

NiRu, ZnRu, SnRu and SnSn mixtures considerably improved the saturation magnetization, M_s with low substitution values; diminishing quickly at the same times the coercivity, H _ci to suitable values for high-density magnetic recording applications. On the other hand, the NiSn mixture also decreased the coercivity rapidly however without enhancing the saturation magnetization. The shown differences on magnetic properties were mainly due both to magnetic nature of divalent ion and to secondary phase apparitions. The mixtures with Sn^2?+? as partner ion diminished markedly to T _c. The tetravalent Ru^4?+? ion has a special effect on magnetic properties of hexagonal ferrites (increases M_s and diminishes fast H _ci with low substitutions).     

The relaxivity of Gd-EOB-DTPA and Gd-DTPA in liver and kidney of the Wistar rat

The NMR relaxivities of Gd-EOB-DTPA and Gd-DTPA were determined in the kidney and liver of intact male Wistar rats immediately following sacrifice and in vitro in solutions and gels, at 1.5 T using a clinical MR scanner. T₁ and T₂ values of tissue samples were derived from spin-echo image sequences. Tissue gadolinium concentrations were determined by radioassay of Gd¹⁵³. Gd-EOB-DTPA T₁ and T₂ relaxivities, R₁ and R₂ (s⁻¹ mmole⁻¹ kg), were found to be 10.7 ± 0.5 and 22.5 ± 3.2, respectively, for liver, 2.4 ± 0.2 and 12.1 ± 1.7 for kidney cortex, 2.7 ± 0.2 and 14.5 ± 1.9 for kidney outer medulla, 2.0 ± 0.2 and 11.4 ± 2.1 for kidney inner medulla. Gd-DTPA R₁ and R₂ were found to be 4.8 ± 0.4 and 14.5 ± 3.7 for liver, 1.2 ± 0.1 and 7.9 ± 0.8 for kidney cortex, 1.6 ± 0.1 and 10.2 ± 1.4 for kidney outer medulla, 1.3 ± 0.1 and 10.2 ± 1.2 for kidney inner medulla. Gd-EOB-DTPA and Gd-DTPA R₁ was increased in liver compared to agarose gels at 38°C (4.49 ± 0.03 and 3.47 ± 0.06), but reduced in kidney tissues. All R₂ were elevated compared to agarose gels at 38°C (5.72 ± 0.12 and 4.12 ± 0.03). Elevated R₂ and R₁ (expressed in terms of the concentration of gadolinium per kg of tissue) can be accounted for in part by the lower water content of tissues compared with gels or solutions, increased microviscosity and binding to macromolecules. In addition, susceptibility effects may give rise to further increases in R₂. By contract, the reduced R₁ observed in kidney may be the result of compartmentalization of the magnetopharmaceuticals. Statistically improved fits were obtained for T₁ recovery curves for liver in the presence of Gd-EOB-DTPA when a dual exponential model was used. Assuming in vitro values for the relaxivities of these artificial contrast agents will lead to inaccuracies when relating observed signal enhancement factors to tissue gadolinium concentration.     

Effect of series resistance on the performance of silicon Schottky diode in the presence of tin oxide layer

The current–voltage (I–V) characteristics of Al/SnO₂/p-Si (MIS) Schottky diodes prepared by means of spray deposition method have been measured at 80, 295 and 350 K. In order to interpret the experimentally observed non-ideal Al/SnO₂/p-Si Schottky diode parameters such as, the series resistance R_s, barrier height Φ_B and ideality factor n, a novel calculation method has been reported by taking into account the applied voltage drop across interfacial oxide layer V_i and ideality factor n in the current transport mechanism. The values obtained for V_i were subtracted from the applied voltage values V and then the values of R_s were recalculated. The parameters obtained by accounting for the voltage drop V_i have been compared with those obtained without considering the above voltage drop. It is shown that the values of R_s estimated from Cheung’s method were strongly temperature-dependent and decreased with increasing temperature. It is shown that the voltage drop across the interfacial layer will increase the ideality factor and the voltage dependence of the I–V characteristics. The interface state density N_ss of the diodes has an exponential growth with bias towards the top of the valance band for each temperature; for example, from 2.37 × 10¹³ eV⁻¹ cm⁻² in 0.70−E_v eV to 7.47 × 10¹³ eV⁻¹ cm⁻² in 0.62−E_v eV for 295 K. The mean N_ss estimated from the I–V measurements decreased with increasing the temperature from 8.29 × 10¹³ to 2.20 × 10¹³ eV⁻¹ cm⁻².     

Effect of diamagnetic substitutions in BaFe12O19 on the magnetic properties

The exchange parameters of BaFe₁₂O₁₉ have been calculated from the temperature dependence of the saturation magnetization using the molecular field theory. Under the assumption that the exchange parameters do not change for diamagnetic substitutions of the Fe³⁺ ions, it is shown that the temperature coefficient of the magnetization at room temperature cannot be decreased without decreasing the magnetization. Diamagnetic substitution in the octahedralf ₂ site would solely increase the saturation magnetization.     

Determination of the kinetic parameters of the isomerization reaction of ethyl isocyanide using HeI photoelectron spectroscopy

The use of HeI photoelectron spectroscopy (PES) for the kinetic study of chemical reactions was introduced previously by us. As another example of the determination of the kinetic parameters of a chemical reaction using the PES method, the isomerization reaction of ethyl isocyanide CH₃CH₂NC → CH₃CH₂CN is investigated. It is found to be first order and the kinetic equations at 193.6, 200.0 and 210.3°C can be expressed as ln R_{466.6 K} = − (7.600 ± 0.026) × 10⁻⁵t − 0.4350; ln R_{473.0 K} = − (1.329 ± 0.032) × 10⁻⁴ − 0.4375 and ln R_{483.3 K} = − (3.170 ± 0.052) × 10⁻⁴ − 0.4354, respectively. The rate constants of the reactions at 193.6, 200.0 reactions at 193.6, 200.0 and 210.3°C are respectively (7.600 ± 0.026) × 10⁻⁵, (1.329 ± 0.032) × 10⁻⁴ and (3.170 ± 0.052) × 10⁻⁴ s⁻¹. The calculated activation energy (E_a) of this isomerization reaction is 38.36 ± 0.32 kcal mol⁻¹. These results are also in excellent agreement with the results obtained by a traditional method. This means that PES is a valuable method for determining the kinetic parameters of chemical reactions. The value of the intercept in the kinetic equations is related to the logarithm of the ratio of the photoionization cross-section of the bands used. This also means that the relative photoionization cross-sections of the bands used for the sample studied are obtained in the kinetic study of a chemical reaction using the PES method.     

Surface demagnetizing field as a source of uniaxial surface anisotropy in GdCoMo thin amorphous films

Surface magnetic anisotropy energy was studied for (Gd_0.26Co_0.74)_0.96Mo_0.04 and (Gd_0.29Co_0.71)_0.96Mo_0.04 thin amorphous films by means of microwave spectroscopy at the X-band within the temperature range 4–295 K. Excitations of surface spin waves were observed in the spin wave resonance spectra. The experiment was performed in a rotating external magnetic field. The angular dependence of the resonance field for the uniform mode (spin wave vector k=0) and the surface mode made it possible to determine the surface uniaxial anisotropy constant K_s and its temperature dependence. An inhomogeneity of the saturation magnetization M_s within a close-to-surface layer of thickness d can generate the surface anisotropy energy with anisotropy constant K_s given by the formula: K_s=4πM^b_s (M^b_s−M^surf_s)d, where the indexes b and surf correspond to the bulk and surface values, respectively. The temperature dependence of K_s calculated by means of the formula agrees qualitatively with temperature dependence of K_s found in the experiment.     

R3(Fe,Mo)29Nx的晶体学特性和内禀磁性

研究了R₃(Fe,Mo)₂₉(R=Ce,Nd,Sm,Gd,Tb,Dy,Y)氮化物的晶体学特性和内禀磁性.主要研究内容为：氮化对R₃(Fe,Mo)₂₉金属间化合物的点阵参数、居里温度T_C、饱和磁化强度σ_s和各向异性场B_a的影响. 关键词：     

Effects of Fe2+ content in raw materials on Mn–Zn ferrite magnetic properties

The magnetic properties of Mn–Zn ferrite such as initial permeability, saturation magnetization, Curie temperature, resistivity and power loss are affected greatly by the Fe²⁺ content in the raw materials. The experimental results show that low resistivity (ρ) and high eddy current loss (P_e) are induced by the superfluous Fe²⁺ content in the raw materials; the scant Fe²⁺ content in the raw materials will increase hysteresis loss (P_h) and decrease Curie temperature (T_c), saturation magnetization (M_s) and initial permeability (μ_i).     

Magnetic properties and formation of Sr ferrite nanoparticle and Zn,Ti/Ir substituted phases

Strontium hexaferrite nanoparticles are prepared by the chemical sol–gel route. Specific saturation magnetization σ_s and coercive field strength H_c are determined depending on the heat treatment of the gel and iron/strontium ratio in the starting solution. These ultrafine powders with single-domain behavior have specific saturation magnetization σ_s=74 emu/g and coercive field strength H_c=6.4 kOe. Experimental results show that it is necessary to preheat the gel between 400 and 500°C for several hours . It can prevent the formation of intermediate γ-Fe₂O₃ and help to obtain ultrafine strontium ferrite single phase with narrow size distribution at a low annealing temperature. Additionally, the magnetic properties of sol–gel derived strontium ferrite with iron substituted by Zn²⁺, Ti⁴⁺ and Ir⁴⁺ are discussed. For an amount of substitution 0<x⩽0.6, the (Zn, Ti)_x substituted strontium ferrite shows higher values of both coercive field strength and saturation magnetization than the (Zn, Ir)_x substituted phase.     

Synthesis, magnetic and dielectric properties of Er-Ni doped Sr-hexaferrite nanomaterials for applications in High density recording media and microwave devices

A sol-gel combustion method has been successfully employed for the synthesis of Sr-hexaferrite nanomaterials doped with Er³⁺ and Ni²⁺ at strontium and iron sites, respectively. The X-ray diffraction analysis confirmed the single magnetoplumbite phase and the crystallite size was found to be in the range of 14-16 nm, suitable for obtaining signal-to-noise ratio in the high density recording media. The magnetic properties such as saturation magnetization (M_s), remanence (M_r) and coercivity (H_c) were calculated from hysteresis loops. M_s, M_r and H_c are observed to increase with the Er-Ni content. The dielectric constant (ε´) and dielectric loss (tan δ) is found to decrease with the increase in frequency and is explained on the basis of Maxwell-Wagner and Koops theory. The decrease in dielectric constant and dielectric loss but increase in saturation magnetization and remanence with Er-Ni content suggests that the materials are suitable for applications in microwave devices and high density recording media .     

Pyroelectric properties of a ferroelectric single crystal [NH2(CH3)2]3Sb2Cl9 (DMACA)

The pyroelectric properties of DMACA single crystals have been measured in the range 135–293 K, revealing the existence of ferroelectric second order phase transition at T_c = 243 K. The saturation value of spontaneous polarization P_s along a-axis amounts to 6.8 × 10⁻³ Cm⁻² at about 203 K. Critical exponent β = 0.5 has been found in the region 0.5–10 K away from T_c.     

Analysis of longitudinal relaxation rate constants from magnetization transfer MR images of human tissues at 0.1 T.

The human calf muscle was examined by using the magnetization transfer MR imaging technique. The time-dependent saturation transfer (TDST) method was applied at low magnetic field 0.1 T in order to measure the mobile water relaxation time T1w, the magnetization transfer rate Rwm from water to solid macromolecules, and the magnetization transfer contrast (MTC) of the human tissue. The magnetization transfer contrast of 0.67 was attained. The transfer rate Rwm was 4.5 sec-1 (+/- 0.3 sec-1) for the anterior tibial muscle and 5.0 sec-1 (+/- 0.4 sec-1) for the gastrocnemius muscles. The values of Rwm are considerably larger than the values of corresponding relaxation rates measured at high fields. The relaxation rate measurements of human tissues in vivo was shown to be possible at 0.1 T even within the framework of normal routine MR imaging. Magnetization transfer MR imaging is a very promising and practical method in order to assess the relaxation processes in heterogeneous human tissues in vivo, and it can improve the tissue characterization possibilities of MR imaging techniques.     

Effective magnetic moments of the europium-monochalcogenides

We have measured the paramagnetic susceptibility and the saturation magnetic moment of a number of polycrystalline samples of all four europium monochalcogenides. Many of them exhibit a negative susceptibility at 2 K and magnetic fields of 70 kOe, rather than the expected saturation behaviour. These anomalies are believed to be due to lattice defects. Reproducible saturation moments have been obtained after subtraction of this linear high field magnetization. Since all materials were nonstoichiometric to within a few percent, the ratio between the Curie-Weiss constantC and the saturation momentM ₀ has been evaluated in order to eliminate the unreliably known numberN of the Eu^{+ +} ions. The quantityR = g _J (J+1) extracted in this way should have the valueR ₀ = 9.00 forg = 2 andJ ≡S = 7/2. The measured values, 9.72, 9.33, 9.32 and 9.50 for EuO, EuS, EuSe and EuTe, respectively, can be correlated directly with the magnetic hyperfine fields, which are ? 305, ? 330, ? 328 and ? 315 kOe in the ferromagnetic aligned states. Both results together lead to the assumption that the magnetic moment per Eu-ion is enhanced over the⁸ S _7/2-value by spin contributions of outer 5d or 6s electrons.     

Measurements of optical parameters of phantom solution and bulk animal tissues in vitro at 650 nm

Optical parameters of bulk animal tissue in vitro, including absorption coefficient (μ_a), reduced scattering coefficient (μ′_s) or scattering coefficient (μ_s), total attenuation coefficient (μ_t), anisotropy factor (g) and refractive index (n) are measured at wavelength of 650 nm. Clinical Intralipid-10% is diluted in distilled water into different concentrations to use as tissue phantoms. Four types of animal tissues in vitro are studied. The relationships among the optical parameters are analyzed systemically. For animal tissues, μ_a, μ′_s or μ_s and n rely on muscle fiber orientations. μ_s and μ_t range from 10 to 20 mm⁻¹, μ_a from 10⁻² to 10⁻³ mm⁻¹ and g from 0.95 to 0.99.     

Ferromagnetic resonance in amorphous systems: Dependence of the relaxation parameter on temperature (magnetization)

We have studied the uniform mode ferromagnetic resonance in the amorphous systems Metglass 28226A, 2826B, 2826 over the temperature range 77–430 K. The data have been analysed in terms of the Gilbert Equation. The g-values are very similar to those of crystalline permalloy. The relaxation parameters λ, are of the order of 10⁸ s^?1 and exhibit an interesting temperature dependence. In particular, for $\text{T}\text{T}{}_{\mathrm{c}}\text{?0.5, λ}$ is simply proportional to the static saturation magnetization M_s. The present results are compared with those obtained on crystalline samples of the 3-d transition metals and their alloys.     

Biosynthesis of gold nanoparticles by Aspergillum sp. WL-Au for degradation of aromatic pollutants

A simple method for synthesis of gold nanoparticles (AuNPs) using Aspergillum sp. WL-Au was presented in this study. According to UV–vis spectra and transmission electron microscopy images, the shape and size of AuNPs were affected by different parameters, including buffer solution, pH, biomass and HAuCl₄ concentrations. Phosphate sodium buffer was more suitable for extracellular synthesis of AuNPs, and the optimal conditions for AuNPs synthesis were pH 7.0, biomass 100 mg/mL and HAuCl₄ 3 mM, leading to the production of spherical and pseudo-spherical nanoparticles. The biosynthesized AuNPs possessed excellent catalytic activities for the reduction of 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, o-nitroaniline and m-nitroaniline in the presence of NaBH₄, and the catalytic rate constants were calculated to be 6.3×10⁻³ s⁻¹, 5.5×10⁻³ s⁻¹, 10.6×10⁻³ s⁻¹, 8.4×10⁻³ s⁻¹ and 13.8×10⁻³ s⁻¹, respectively. The AuNPs were also able to catalyze the decolorization of various azo dyes (e.g. Cationic Red X-GRL, Acid Orange II and Acid scarlet GR) using NaBH₄ as the reductant, and the decolorization rates reached 91.0–96.4% within 7 min. The present study should provide a potential candidate for green synthesis of AuNPs, which could serve as efficient catalysts for aromatic pollutants degradation.