On- and off-resonance spin-lock MR imaging of normal human brain at 0.1 T: possibilities to modify image contrast

The aim of the present investigation was to determine spin lock (SL) relaxation parameters for the normal brain tissues and thus, to provide basis for optimizing the imaging contrast at 0.1 T. 68 healthy volunteers were included. On-resonance spin lock relaxation time (T_1ρ) and off-resonance spin lock relaxation parameters (T_1ρ^off, M_e/M_o), MT parameters (T_1sat, M_s/M_o), and T₁, T₂ were determined for the cortical gray matter, and for the frontal and parietal white matters. The T_1ρ for the frontal and parietal white matters ranged from 110 to 133 ms and from 122 to 155 ms with locking field strengths from 50 μT to 250 μT, respectively. Accordingly, the values for the gray matter ranged from 127 to 155 ms. With a locking field strength of 50 μT, T_1ρ^off for the frontal and parietal white matters were from 114 to 217 ms and from 126 to 219 ms, and for the gray matter from 136 to 267 ms with the angle between the effective magnetic field (B_eff) and the z-axis (θ) ranging from 60° to 15°, respectively. The T_1ρ of the white and gray matters increased significantly with increasing locking field amplitude (p < 0.001). The T_1ρ^off decreased significantly with increasing θ (p < 0.001). T_1ρ and T_1ρ^off with θ ≥ 30° were statistically significantly shorter in the frontal than in the parietal white matters (p < 0.05). The duration, amplitude and θ of the locking pulse provide additional parameters to optimize contrast in brain SL imaging.     

On the dielectric loss and thermal bleaching of calcite irradiated by X-rays

The changes produced by X-ray irradiation in the dielectric and optical properties of calcite crystals are reported. At ordinary temperatures, the dielectric constant as well as the dielectric loss of the uncoloured crystal remains practically unchanged in the frequency region of 10 kc/s-15 Mc/s. It has been found that the temperature variation of its dielectric loss can be represented by an equation tan where A and B are constants; this is attributed to the movement of vacancies in the crystal.

On irradiation by X-rays, calcite exhibits pronounced optical absorption in the ultraviolet region beyond 400 mμ; the dielectric loss of calcite also increases considerably on colouration. The thermoluminescence shows a very strong glow peak at 85°C with minor ones at higher temperatures. During thermal bleaching, the dielectric loss of the coloured crystal shows a prominent maximum in the temperature range 70–120°C and beyond 230°C, it varies in the same way as in the case of the uncoloured crystal. The correspondence between the change in dielectric loss and the first glow peak is possibly due to thermal release of trapped electrons. The optical absorption disappears when the crystal is heated to 350°C and on cooling to room temperature, its dielectric loss returns to its original value before colouration.     

Oxidation of heated diamond C(100):H surfaces

This paper extends a previous study (Pehrsson and Mercer, submitted to Surf. Sci.) on unheated, hydrogenated, natural diamond (100) surfaces oxidized with thermally activated oxygen (O^*₂). In this paper, the oxidation is performed at substrate temperatures from T_sub=24 to 670°C. The diamond surface composition and structure were then investigated with high resolution electron energy loss spectroscopy (HREELS), Auger electron spectroscopy (AES), electron loss spectroscopy (ELS) and low energy electron diffraction (LEED).

The oxygen coverage (θ) increased in two stages, as it did during oxidation at T<80°C. However, there are fundamental differences between the oxidation of nominally unheated and heated diamond surfaces. This difference is attributed to simultaneous adsorption and rapid desorption of oxygen species at higher temperatures; the desorption step is much slower without heating. The initial oxidation rates were similar regardless of the substrate temperatures, but the peak coverage (θ) was lower at higher temperatures. For example, θ plateaued at 0.4±0.1 ML at 600°C. The lower saturation coverage is again attributed to oxygen desorption during oxidation. Consistent results were obtained on fully oxidized surfaces, which when heated in vacuum to T_sub=600°C, lost 60% of their adsorbed oxygen. ELS revealed few C=C dimers on the oxidized surfaces, and more graphitization than on unheated surfaces. Oxidation at elevated temperatures also increased the carbonyl to ether ratio, reflecting etching-induced changes in the types of surface sites. The carbonyl and C–H stretch frequencies increased with oxygen dose due to formation of higher oxidation states and/or hydrogen bonding between adjacent groups. The oxygen types did not interconvert when the oxidized surfaces were heated in vacuum. Oxygen desorption generated a much more reactive surface than heating-induced dehydrogenation of the smooth, hydrogenated surface.     

Chlorine/silicon surface reactions under heating

Reactions on Cl-adsorbed Si(111) and Si(100) surfaces—(Cl/Si(111) and Cl/Si(100))—under heating in ultrahigh vacuum (UHV) and in a Cl₂ atmosphere were studied. Auger electron spectroscopy (AES) and low-energy electron energy loss spectroscopy (LEELS) were used for examination of surface changes. Heating in UHV at 820°C for 30 s successfully removed almost all Cl atoms, both on Cl/Si(111) and Cl/Si(100). Variance in LEELS spectra shows that decomposition of SiCl_x (x > 1), a small amount of which was present on Cl/Si(111), occurs under heating on Si(111) both in UHV and in Cl₂ and desorbs reaction products, leaving the Si---Cl bonds on the surfaces. Such Si---Cl bonds specific to those on Cl/Si(111) are formed also on Cl/Si(100) heated in C1₂ at 820°C. On Cl/Si(100) heated in C1₂, there are various surface changes: relaxation of the 2 × 1 structure remaining on the Cl/Si(100), desorption of reaction products, and formation of Si---Cl bonds specific to those on Cl/Si(111). The Si---Cl bonds, both on Cl/Si(111) and Cl/Si(100), decomposed under longer heating and under heating at higher temperatures in UHV.     

Evaluation of the structure (or nonlinearity) parameter x by peak-shift method from volumetric heating data of PET

The structure parameter x, defining the temperature and structure relative contribution to the relaxation times, was evaluated applying the peak-shift method (PSM) onto volumetric heating data of poly(ethylene terephthalate) (PET) with content of crystallinity 2.6 wt%. The method of mercury-in-glass (MIG) dilatometry and three-step thermal cycle procedure were used. Two sets of heating scans were measured as a function of the amount of volume isothermal relaxation for two different relaxation temperatures below T_g (60 and 52 °C), whereas other experimental variables were kept constant. The experimentally determined heating isobar inflection temperature is a linear function of the amount of volume relaxation, which satisfies the application of PSM method for structure parameter x determination from volumetric heating data. The value of structure parameter of the used PET is independent of relaxation temperature and equal to 0.50±0.02. Finally, the shift of heating isobar inflection temperature with relaxation temperature (60, 56, 52 and 48 °C) measured for constant amount of volume isothermal relaxation was found to be linear, with the slope of 0.13.     

Time evolution of interface roughness during thermal oxidation on Si(0 0 1)

The surface morphological change at an initial stage of thermal oxidation on Si(0 0 1) surface with O₂ was investigated as a function of oxide coverage by a real-time monitoring method of Auger electron spectroscopy (AES) combined with reflection high energy electron diffraction (RHEED). At 653 °C where oxide islands grow laterally, protrusions were observed to develop under the oxide islands as a consequence of concurrent etching of the surface. The rate of etching was measured from a periodic oscillation of RHEED half-order spot intensity I_(1/2,0) and I_(0,1/2). At 549 °C where Langmuir-type adsorption proceeds, it was observed that both I_(1/2,0) and I_(0,1/2) decrease more rapidly in comparison with an increase of oxide coverage and the intensity ratio between them decreases gradually with O₂ exposure time. These suggest that Langmuir-type adsorption occurs at sites where O₂ adsorbs randomly, leading to subdivision of the 2×1 and 1×2 domains by oxidized regions, and that Si atoms are ejected due to volume expansion in oxidation to change the ratio between 2×1 and 1×2 domains.     

Atom probe tomography of 15Kh2MFA Cr–Mo–V steel surveillance specimens

An atom probe study has been performed on 15Kh2MFA base and 10KhMFT weld metal surveillance specimens from a VVER-440/213C reactor to investigate the mechanisms that produce embrittlement in low copper materials during service. The composition of the base metal was Fe-0.06 at.% Cu, 3.1% Cr, 0.34% V, 0.46% Mn, 0.35% Mo, 0.07% Ni, 0.34% Si, 0.74% C, 0.025% P, and 0.028% S. The base material was characterized after thermal aging for 10 years at 295°C and after neutron irradiation at 270°C for 10 years to a fluence of 1.0×10²⁵ m⁻² (E>0.5 MeV). The ductile-to-brittle transition temperatures (DBTT) of the base metal were −49, −70 and 141°C, for the unirradiated, thermally aged and neutron irradiated conditions, respectively. The composition of the weld metal was Fe-0.05 at.% Cu, 1.46% Cr, 0.22% V, 1.11% Mn, 0.29% Mo, 1.17% Si, 0.17% C, 0.02% P, and 0.029% S. The weld material was characterized after tempering for 18 h at 690°C plus a simulated stress relief treatment of 43.5 h at 680°C, after thermal aging for 5 years at 295°C, and after neutron irradiation at 275°C for 5 years to a fluence of 5.2×10²⁴ m² (E>0.5 MeV). The DBTTs were 7, 11 and 123°C, respectively, for these three conditions. A high number density of ultrafine manganese- and silicon-enriched regions was observed in both neutron-irradiated materials. Phosphorus segregation was observed at the VC-matrix interface and at grain boundaries.     

Ln1−xSrxCoO3(Ln = Sm, Dy) for the electrode of solid oxide fuel cells

The perovskite-type oxides were synthesized in the series of Ln_1−xSr_xCoO₃(Ln = Sm, Dy). The formation of solid solutions in Dy_{1 − x}Sr_xCoO₃ was limited, compared with that in Sm_{1 − x}Sr_xCoO₃. The electrical conductivities of the sintered samples were measured as a function of x in the temperature range 30 to 1000 °C. The highest conductivity of around 500 S/cm at 1000 °C was found in Sm_0.7Sr_0.3CoO₃. The reactivity of all the samples with YSZ was examined at 800–1000 °C for 96 h. The Sr-doped perovskite oxides were more reactive with YSZ and produced SrZrO₃ at 900 °C after 96 h. However, no reaction product between SmCoO₃ and YSZ was observed at 1000 °C for 96 h. The cathodic polarization of the oxide electrodes, sputtered on yttria stabilized zirconia (YSZ), was studied at 800–1000 °C in air. SmCoO₃ shows no degradation of the electrode performance at higher temperatures. The thermal expansion measurements on the sintered samples were carried out from room temperature to 1000 °C. Large thermal expansion coefficients were found in these samples.     

Crystallization kinetics in ferroelectric thin films: Viability of atomic force microscopy

The pyrochlore to perovskite phase transformation was studied in lead zirconate titanate (PZT) thin films. The films were fabricated on platinum electrodes and annealed by rapid thermal processing (RTP). The phases which formed and their location in the film were analyzed using glancing angle XRD and depth profiling was demonstrated. Grain size and structure, nucleation sites and surface morphology were determined with transmission electron microscop (TEM) and atomic force microscopy (AFM). The role of AFM in this type of transformation study was assessed.

The PZT films crystallized with a (100) orientation which was preferentially nucleated at the platinum/film interface. RTP at 650°C for 15 s was sufficient to complete the transformation. However, columnar grain growth and improvements in the ferroelectric properties were obtained with increased RTP time. A PZT film with RTP at 650°C for 1 min possessed a remanent polarization of 25 μC/cm² and a dielectric constant of ε = 650.     

Proton conductive amorphous thin films of tungsten oxide clusters with acidic ligands

Three kinds of peroxo-polytungstic acid (PPTA, C-PPTA and N-PPTA) were obtained by reacting hydrogen peroxide with metallic tungsten, tungsten carbide or tungsten nitride, respectively. Polytungstates, C-PPTA and N-PPTA, were found to contain oxalate and nitrate ligands. Their proton conductivities were compared using thin film specimens spin-coated from their water solution. Conductivity of each as-coated film was in the range from 10⁻³ to 10⁻⁴ S cm⁻¹ under the relative humidity of 40% (25 °C). A sharp decrease in conductivity (to less than 10⁻⁷ S cm⁻¹ at 25 °C) was observed for PPTA without acidic ligands after thermal treatment at 80 °C. However, the effect of thermal treatment on C-PPTA or N-PPTA was much milder. A 80 °C-treated C-PPTA film showed the conductivity of 1.0 × 10⁻⁵ S cm⁻¹ (25 °C) with a very weak dependency on ambient humidity.     

In vivo NMR T2 relaxation of experimental brain tumors in the cat: a multiparameter tissue characterization.

Experimental gliomas (F98) were inoculated in cat brain for the systematic study of their in vivo T₂ relaxation time behavior. With a CPMG multi-echo imaging sequence, a train of 16 echoes was evaluated to obtain the transverse relaxation time and the magnetization M(0) at time T = 0. The magnetization decay curves were analyzed for biexponentiality. All tissues showed monoexponential T₂, only that of the ventricular fluid and part of the vital tumor tissue were biexponential. Based on these NMR relaxation parameters the tissues were characterized, their correct assignment being assured by comparison with histological slices. T₂ of normal grey and white matter was 74 ± 6 and 72 ± 6 msec, respectively. These two tissue types were distinguished through M(0) which for white matter was only 0.88 of the intensity of grey matter in full agreement with water content, determined from tissue specimens. At the time of maximal tumor growth and edema spread a tissue differentiation was possible in NMR relaxation parameter images. Separation of the three tissue groups of normal tissue, tumor and edema was based on T₂ with T_2(normal) < T_2(tumor) < T_2(edema). Using M(0) as a second parameter the differentiation was supported, in particular between white matter and tumor or edema. Animals were studied at 1–4 wk after tumor implantation to study tumor development. The magnetization M(0) of both tumor and peritumoral edema went through a maximum between the second and third week of tumor growth. T₂ of edema was maximal at the same time with 133 ± 4 msec, while the relaxation time of tumor continued to increase during the whole growth period, reaching values of 114 ± 12 msec at the fourth week. Thus, a complete characterization of pathological tissues with NMR relaxometry must include a detailed study of the developmental changes of these tissues to assure correct experimental conditions for the goal of optimal contrast between normal and pathological regions in the NMR images.     

Polymer electrolyte plasticized with PEG-borate ester having high ionic conductivity and thermal stability

We have focused on the PEG-borate ester as a new type of plasticizer for solid polymer electrolyte composed of poly(ethyleneglycol) methacrylate (PEGMA) and lithium bis-trifluoromethanesulfonimide (LiTFSI). The PEG-borate ester shows good thermal stability and high flash point. Ionic conductivity of the polymer electrolyte increases with increasing amount of the PEG-borate ester and exhibits values greater than 10⁻⁴ S cm⁻¹ at 30 °C and 10⁻³ S cm⁻¹ at 60 °C. Furthermore, PEG-borate ester has three EO chains whose lengths are variable, and various ionic conductivities are expected to depend on EO chain length. As a result, polymer electrolyte containing the PEG-borate ester whose EO chain length is n=3 shows highest ionic conductivity. Furthermore, polymer electrolytes containing PEG-borate esters show excellent thermal and electrochemical stability. The electrolytes are thermally stable up to 300 °C and electrochemically up to 4.5 V vs. Li⁺/Li.     

RF-sputtered CrB2 diffusion barrier for Ni/Au Ohmic contacts on p-CuCrO2

Ohmic contacts to p-type CuCrO₂ using Ni/Au/CrB₂/Ti/Au contact metallurgy are reported. The samples were annealed in the 200–700 °C range for 60 s in flowing oxygen ambient. A minimum specific contact resistance of 2 × 10⁻⁵ Ω cm² was obtained after annealing at 400 °C. Further increase in the annealing temperature (>400 °C) resulted in the degradation of contact resistance. Auger Electron Spectroscopy (AES) depth profiling showed that out-diffusion of Ti to the surface of the contact stacks was evident by 400 °C, followed by Cr at higher temperature. The CrB₂ diffusion barrier decreases the specific contact resistance by almost two orders of magnitude relative to Ni/Au alone.     

Low temperature fabrication of vanadium oxide films for uncooled bolometric detectors

Vanadium oxide films with temperature coefficient of resistant of −2.6% K⁻¹ have been fabricated on Si₃N₄-film-coated Si substrates by ion beam sputtering in a controlled Ar/O₂ atmosphere, at a relatively low growth temperature of 200 °C. The as-deposited films show no semiconductor-to-metal phase transitions even heated up to 150 °C. X-ray diffractometry shows that the main compound of the VO_x film is a metastable phase of vanadium dioxide (VO₂(B)) and the VO₂(B) film can be transformed into VO₂ film by post-growth annealing at 450 °C in flowing Ar atmosphere.     

Quantitative myocardial distribution volume from dynamic contrast-enhanced MRI

The objective of this study was to investigate if dynamic contrast-enhanced magnetic resonance imaging (MRI) can be used to quantitate the distribution volume (v_e) in regions of normal and infarcted myocardium. v_e reflects the volume of the extracellular, extravascular space within the myocardial tissue. In regions of the heart where an infarct has occurred, the loss of viable cardiac cells results in an elevated v_e compared to normal regions. A quantitative estimate of the magnitude and spatial distribution of v_e is significant because it may provide information complementary to delayed enhancement MRI alone.

Using a hybrid gradient echo–echoplanar imaging pulse sequence on a 1.5T MRI scanner, 12 normal subjects and four infarct patients were imaged dynamically, during the injection of a contrast agent, to measure the regional blood and tissue enhancement in the left ventricular (LV) myocardium. Seven of the normal subjects and all of the infarct patients were also imaged at steady-state contrast enhancement to estimate the steady-state ratio of contrast agent in the tissue and blood (Ct/Cb) — a validated measure of v_e. Normal and infarct regions of the LV were manually selected, and the blood and tissue enhancement curves were fit to a compartment model to estimate v_e. Also, the effect of the vascular blood signal on estimates of v_e was evaluated using simulations and in the dynamic and steady-state studies.

Aggregate estimates of v_e were 23.6±6.3% in normal myocardium and 45.7±3.4% in regions of infarct. These results were not significantly different from the reference standards of Ct/Cb (22.9±6.8% and 42.6±6.3%, P=.073). From the dynamic contrast-enhanced studies, approximately 1 min of scan time was necessary to estimate v_e in the normal myocardium to within 10% of the steady-state estimate. In regions of infarct, up to 3 min of dynamic data were required to estimate v_e to within 10% of the steady-state v_e value.

By measuring the kinetics of blood and tissue enhancement in the myocardium during an extended dynamic contrast enhanced MRI study, v_e may be estimated using compartment modeling.     

Quantitative NumART2* mapping in functional MRI studies at 1.5 T

Quantitative mapping of the effective transverse relaxation time, T₂* and proton density was performed in a motor activation functional MRI (fMRI) study using multi-echo, echo planar imaging (EPI) and NumART₂* (Numerical Algorithm for Real time T₂*). Comparisons between NumART₂* and conventional single echo EPI with an echo time of 64 ms were performed for five healthy participants examined twice. Simulations were also performed to address specific issues associated with the two techniques, such as echo time-dependent signal variation. While the single echo contrast varied with the baseline T₂* value, relative changes in T₂* remained unaffected. Statistical analysis of the T₂* maps yielded fMRI activation patterns with an improved statistical detection relative to conventional EPI but with less activated voxels, suggesting that NumART₂* has superior spatial specificity. Two effects, inflow and dephasing, that may explain this finding were investigated. Particularly, a statistically significant increase in proton density was found in a brain area that was detected as activated by conventional EPI but not by NumART₂* while no such changes were observed in brain areas that showed stimulus correlated signal changes on T₂* maps.     

Pulsed nuclear magnetic resonance of gamma-irradiated lithium hydride

Some of the effects of ⁶⁰Co gamma irradiation on lithium hydride are described. Volume increase and nuclear magnetic resonance data are given for samples irradiated from 40 to 395°C. Maximum swelling occurs between 160 and 200°C; negligible swelling occurs above 300°C. Motionally narrowed proton and ⁷Li nuclear magnetic resonance signals appear on irradiation and increase with increasing swelling. These decomposition products, which are trapped inside the LiH, can amount to more than one-tenth the total sample at doses of 50 Grad. At this point, 25 volume per cent swelling has occurred and the growth rate has subsided. The hydrogen nuclear magnetic resonance signal has been shown to come from H₂ molecules by observation of the ortho-para conversion on cooling. Hydrogen densities derived independently from the longitudinal relaxation time and the swelling data are in reasonable agreement. The corresponding gas pressures range from 750 to 5000 atm. The H₂ is thought to be in bubbles which cause the volume growth, and recent electron microscopy results support this view. The ⁷Li signal has a Knight shift, and the lithium is present as metal particles. Above 200°C, the H₂ and Li back-react rapidly. Above 300°C this reaction takes place as fast as the decomposition, which was caused by the irradiation.     

Proton conductivity of phosphoric acid derivative of fullerene

The proton conductive property of methano [60] fullerene diphosphoric acid has been investigated under various humidity conditions at the temperature range between 15 and 45 °C. It shows proton conductivity as high as 10⁻² S cm⁻¹ at 25 °C under relative humidity of 95%. Thermal analyses including TG–DTA and thermal desorption mass spectroscopy (TDS) confirm that the compound is thermally stable up to 200 °C. Proton conduction of the compound depends very much on humidity or water content. The logarithmic conductivity at 25 °C is increased linearly with increasing relative humidity. The activation energy (E_a) estimated from the slope of log(σT) vs. 1/T is decreased from 1.08 to 0.52 eV, as the relative humidity is increased from 40% to 75%. The humidity dependence of conductivity is discussed in the light of the observed hydration isotherm.     

慢性电刺激海马结构诱发大鼠脑磁共振成像异常信号分析

为探讨海马结构(hippocampal formation)功能失衡与癫痫源性脑损伤的关系,本工作采用 慢性强直电刺激大鼠海马(hippocampus, HPC) CA1顶树突区（apical dendrite region, A DR）或齿状回（dentate gyrus, DG）诱发大鼠癫痫模型,一天一次,连续刺激6～8天后, 观察人工致痫灶以外的横向弛豫时间加权的核磁共振(T₂ weighted magnetic reson ance im age, T₂-WI) 绝对信号值变化（片厚1mm）,以及深部电图和原发性湿狗颤抖（pri mary wet dog shakes, WEDS）,并对被检测动物T₂-WI信号异常的相应脑区进行组织学鉴定. 结果表明：（1）电 刺激大 鼠ADR或DG的作用基本相似,引起深部电图的癫痫样电活动和侧脑室区域T₂值增强.（2）含有电极尖端痕迹的核磁共振（magnetic resonance image,MRI）脑切片出现对称性腹部侧脑室区域T₂值增强,连续向后1mm取MRI脑切片进行观察发现,对侧腹部侧脑室区域信号异常. （3）组织学切片观察到：MRI检测的侧脑室区域T₂-WI信号增强与组织切片的侧脑室扩大相吻合,可见扩大的侧脑室中脉络丛上皮细胞病理性增生现象. 提示：在大鼠癫痫点燃现象出现之前,过度激活DG或ADR均可引起相似的早期癫痫源性脑损伤.     

Ion transport studies in calcium alginate gels by magnetic resonance microscopy

Polyelectrolyte biopolymers such as calcium alginate are becoming increasingly important for the recovery of heavy metals from aqueous solutions. To understand the mechanism of ion transport in these biopolymer systems, the transport of copper ions into calcium alginate gels was investigated using proton nuclear magnetic resonance (NMR) microscopy. Copper ion transport was imaged using an inversion recovery technique which utilizes the paramagnetic effect of copper on water proton relaxation times. Diffusion experiments were performed in a diffusion cell designed to approximate a semi-infinite slab geometry at temperatures between 278 and 313 K using copper reservoir concentrations between 10 and 60 mM. The diffusion coefficient of copper in these gels was calculated from the NMR data to fit a combined diffusion-reaction model involving a diffusion term (D) and a kinetic binding term (k). At 23 °C, the diffusion coefficients in 1, 2, and 3% (w/v) gels were 3.1 · 10⁻¹⁰, 2.0 · 10⁻¹⁰, and 1.4 · 10⁻¹⁰ m²/s, respectively. The activation energy for diffusion in the 2% (w/v) gel was 28 kJ/mol.