The accuracy of whole brain N-acetylaspartate quantification

A non-localizing pulse sequence to quantify the total amount of N-acetylaspartate (NAA) in the whole brain (WBNAA) was introduced recently [Magn. Reson. Med. 40, 684–689 (1998)]. However, it is known that regional magnetic field inhomogeneities, ΔB₀s, arising from susceptibility differences at tissue interfaces, shift and broaden local resonances to outside the integration window, leading to an underestimation of the true amount of NAA in the entire brain. To quantify the upper limit of this loss, the whole-head proton MR spectrum (¹H-MRS) of the water was integrated over the same frequency width as the NAA. The ratio of this area/total-water-line was 75 ± 5% in 5 volunteers. The procedure was repeated with the brain-only water peak, obtained by summing signals only from voxels within that organ from a three-dimensional chemical-shift-imaging (3D CSI) set. It indicated that <10% of the water signal loss occurred in the brain. Therefore, by analogy, WBNAA accounts for >90% of that metabolite.     

Application of Proton Chemical Shift Imaging in Monitoring of Gamma Knife Radiosurgery on Brain Tumors

Our objective was to assess proton chemical shift imaging for potential clinical application in monitoring response to gamma knife radiosurgery. Twenty-five proton chemical shift imaging studies and conventional magnetic resonance images were performed on six patients with intracranial tumors. The peak areas of N-acetylaspartate, choline-containing compounds (Cho), creatine, and lipids were calculated and normalized to N-acetylaspartate in the contralateral hemisphere. The spectra from the lesion before treatment showed a relatively high Cho peak, reported as a characteristic spectrum of tumors. Tumor size and Cho level after radiosurgery did not increase except in two cases. In these cases, radiation necrosis was observed with elevated Cho and a mobile lipid peak. Stable or decreased Cho seems to suggest a loss of tumor viability, and changes in Cho indicate the effectiveness of radiosurgery. Increasing Cho and the appearance of the mobile lipid peak may distinguish radiation necrosis from recurrent tumors, which cannot be distinguished by magnetic resonance imaging.     

The effect of boron ion implantation and annealing on the microstructure and electrical characteristics of the diamond films

Diamond films were doped by boron ion-implantation with the energy of 120 keV. The implantation dose ranged from 10¹⁴ to 10¹⁷ cm⁻². After the implantation, the diamond films were annealed at different temperatures (600–750°C) for different times (2–15 min). Scanning Electronic Microscope, Raman and Secondary Ion Mass-spectrum were used to investigate the effect of boron ion implantation and annealing on the microstructure of the diamond films. The electrical resistivities of the diamond films were also measured. It was found that the best dose of boron ion-implantation into the diamond film was around 10¹⁶ cm⁻². The appropriate annealing temperature and time was 700°C and 2–5 min, respectively. After implantation, the resistivities were reduced to 0.1 Ω cm (almost nine orders lower than the unimplanted diamond films). These results show that boron ion implantation can be an effective way to fabricate P-type diamond films.     

Near-infrared absorptions of monomethylhydrazine

The peak absorption coefficients for two near-infrared absorptions of monomethylhydrazine, CH₃-N₂H₃, (MMH) were measured. Absorption bands located at 1.524 μm (6560 cm^-1), 1.557 μm (6423 cm^-1), and 1.583 μm (6316 cm^-1) are assigned to the υ = 2 overtones of the infrared N-H stretching fundamentals at 3317, 3245 and 3177 cm^-1. An absorption band located at 1.04 μm (9620±100 cm^-1) is assigned to the υ = 3 overtone of one of these fundamentals. The peak absorption coefficients (₁₀) at 1.524 μm (6560±20 cm^-1) and 1.04 μm (9620±100 cm^-1) are 31 × 10^-3 and 0.97 × 10^-3 (cm atm)^-1, respectively. Uncertainties in these coefficients were estimated to be less than ±20% due primarily to uncertainties in the partial vapor pressure of MMH.     

The temperature dependence of the short wavelength transmittance limit of vacuum ultraviolet window materials—I. Experiment

The short wavelength transmittance limit or cut-off wavelength, λ_co, of LiF, MgF₂, CaF₂, LaF₃, BaF₂, sapphire, synthetic crystal quartz and fused quartz has been measured from about 100°C to about 10°K. λ_co is not a well denned quantity, so for the purpose of this experiment it has been arbitrarily taken as the wavelength where transmittance could just be measured, usually 0.1-0.5 per cent. With one exception λ_co shifted to shorter wavelengths as the sample was cooled; the shift varied from about 40 to 80 Å over the temperature range from 100°C to 10°K, depending on the material, with the largest shift occurring in BaF₂;. The exception was LaF₃ which showed no measurable change in λ_co wth temperature. Over the temperature range from 20° to 100°C the slope of λ_co, with temperature for all materials was fairly constant, but below 20°C it decreased, approaching zero as the temperature approached 20°-10°K. In the case of synthetic crystal quartz, for example, the slope changed from about 0.28 Å/°K at room temperature to about 0.055 Å/°K at 80°K.     

Magnetic properties of Sm–Co–B-based nanocomposite magnets

The magnetic properties of nanocomposite melt-spun magnets with composition Sm_16−xCo_68+xB₁₆ (x=0–10, 2 at% interval) and Sm₈Co_92−yB_y (y=10–18, 2 at% interval) have been studied systematically. Several ribbons were fabricated with a wheel speed of 50 m/s, followed by annealing in the temperature range of 700–800°C for 2.5–40 min. XRD results and magnetization versus temperature curves showed that almost all of the samples were composed of the tetragonal Sm₂Co₁₄B and rhombohedral SmCo₁₂B₆ phases which are not magnetically hard at room temperature. However, a relatively high coercivity in the range of 3.5–5.5 kOe has been obtained in these samples. The highest coercivity of 5.5 kOe and a very promising β value of −0.28%/°C were obtained in Sm₈Co₇₄B₁₈ ribbons annealed at 750°C for 5 min. The high coercivities are attributed to the small grain size of the 2 : 14 : 1 phase, in which the large surface areas enhance its effective anisotropy, and make it uniaxial type.     

Defect versus nanocrystal luminescence emitted from room temperature and hot-implanted SiO2 layers

Silicon nanocrystals have been synthesized in SiO₂ matrix using Si ion implantation. Si ions were implanted into 300-nm-thick SiO₂ films grown on crystalline Si at energies of 30–55 keV, and with doses of 5×10¹⁵, 3×10¹⁶, and 1×10¹⁷ cm⁻². Implanted samples were subsequently annealed in an N₂ ambient at 500–1100°C during various periods. Photoluminescence spectra for the sample implanted with 1×10¹⁷ cm⁻² at 55 keV show that red luminescence (750 nm) related to Si-nanocrystals clearly increases with annealing temperature and time in intensity, and that weak orange luminescence (600 nm) is observed after annealing at low temperatures of 500°C and 800°C. The luminescence around 600 nm becomes very intense when a thin SiO₂ sample is implanted at a substrate temperature of 400°C with an energy of 30 keV and a low dose of 5×10¹⁵ cm⁻². It vanishes after annealing at 800°C for 30 min. We conclude that this luminescence observed around 600 nm is caused by some radiative defects formed in Si-implanted SiO₂.     

Synthesizing 0.9PZN–0.1BT by mechanically activating mixed oxides

0.9Pb(Zn_1/3Nb_2/3)–0.1BaTiO₃ (0.9PZN–0.1BT) of perovskite structure has been successfully prepared by mechanically activating mixed oxides of PbO, ZnO, Nb₂O₅, BaO and TiO₂. The novel mechanochemical technique skips the phase-forming calcination step at an intermediate temperature that is always required in both the conventional solid state reaction and chemistry-based precursor routes. Ultrafine 0.9PZN–0.1BT particles of perovskite structure were formed when the constituent oxides were mechanically activated for more than 10 h. The powder was sintered to a density of 96% theoretical density at 1100°C for 1 h. The sintered 0.9PZN–0.1BT exhibits perovskite structure and a peak dielectric constant of 8800 at the Curie temperature of 60°C when measured at a frequency of 100 Hz.     

The beneficial influence of ultrasound in the polymerization of epsilon-caprolactam to polyamide-6 (Nylon 6). Part II: additional experiment to understand the "pre-sonication effect"

Ultrasound (US) “pre-sonication effect” is the beneficial effect of US in the hydrolytic polymerization of ε-caprolactam (CL) mixtures with very low water concentrations (about 0.1–1 wt%). It appears after a mild initial treatment of the mixtures with US [17.5–20 kHz, short times (5–15 min), low temperatures (70–110 °C)] followed by heating at 220–260 °C. An explanation is proposed on the basis of the formation in mild conditions (100 °C) of low concentrations of cyclic oligomers never detected in the literature at those conditions. These, under US irradiation, produce linear amino acid oligomers, which are strong activators of polymerization when the mixture of CL and water, after US irradiation, is heated at the suitable polymerization temperature indicated above.     

Oxygen tracer diffusion in La1 − xSrxCoO3

Tracer diffusion of ¹⁸O in dense, polycrystalline La_1−xSr_xCoO₃ for x = 0.1 has been measured in the temperature range 400 to 600 °C and at 500 °C for x = 0.2 at an oxygen partial pressure of 1 × 10⁵ Pa. Depth profiles were obtained by secondary ion mass spectrometry. The diffusion coefficient for La_0.9Sr_0.1CoO₃ is given by D = (17–247) exp[(−232 ± 8 kJ/mole)/RT] cm²/s. This value is several orders of magnitude lower than D extrapolated from the results for x = 0.2 measured in the 700–900 °C temperature range. One possible explanation for the discrepancy is that the two measurements reflect different diffusion paths. As expected, La_0.8Sr_0.2CoO₃ exhibits a higher diffusivity at 500 °C than does La_0.9Sr_0.1CoO₃.     

Dissociation between lactate accumulation and acidosis in middle cerebral artery-occluded rats assessed by P and H NMR metabolic images under A 2-T magnetic field

The relationships among tissue edema, lactate accumulation, and intracellular pH in middle cerebral artery (MCA)-occluded rats were investigated with multiecho ¹H magnetic resonance imaging and spatially resolved metabolic images constructed by ¹H and ³¹P nuclear magnetic resonance (NMR) chemical shift imaging (CSI). For the effective and sensitive detection of NMR signals from the brain, outer volume suppression (OVS), reduced k-space sampling and proton irradiation were incorporated into the CSI sequences. The consecutive three measurements of calculated T₂ image, lactate image, and pH image which were required for 3.75 h were repeated for four cycles of 1–16 h after MCA occlusion. Tissue edema and lactate accumulation in the infarcted region were gradually and consistently increased during the 15-h observation period. In contrast, severe acidosis was already detected on the first pH image (2–4.7 h after MCA occlusion); thereafter, the degree of acidosis became milder and showed no further progression. The dissociation between the time courses of the lactate accumulation and pH decrease was clearly demonstrated by the NMR metabolic images. Acid-base balance in cerebral infarction might be affected not only by lactate production but also by complicated interactions with tissue edema and some other factors.     

Macroscopic tumor volume of malignant glioma determined by contrast-enhanced magnetic resonance imaging with and without magnetization transfer contrast

The purposes of this study were to compare the conspicuity and lesion volume of contrast-enhancing macroscopic malignant glioma determined by postcontrast magnetic resonance (MR) imaging with and without magnetization transfer (MT) saturation, and to discuss possible implications for radiotherapy planning. Nineteen patients (age 24–60 years) with histologically proven malignant glioma were prospectively examined by MR imaging. After the administration of gadolinium dimeglumine (0.1 mmol/kg body weight), the lesions were imaged with an MT-weighted FLASH (fast, low-angle shot) pulse sequence and with a conventional T₁-weighted spin-echo (SE) sequence without MT saturation. The mean tumor volumes of gliomas measured on MT-weighted FLASH images were significantly (p < .01) larger than those obtained from T₁-weighted SE images (45 ± 15 cm³ vs. 33 ± 10 cm³). The mean contrast-to-noise ratio of enhancing lesions on MT-weighted FLASH was 48 ± 14 compared with 30 ± 14 on SE images, representing a significant (p < .01) improvement. We conclude that the volume of contrast enhancement of malignant glioma identified on MT-weighted FLASH images represents the area of disrupted blood-brain barrier. If this volume of subtle contrast enhancement is caused by tumor infiltration and represents the boost target volume for stereotactic radiosurgery or brachytherapy, MT-weighted FLASH images would be better than T₁-weighted SE images to define these volumes. These improved delineation of areas at highest risk for recurrence following radiation therapy should enhance the efficacy of treatment planning for high-boost therapy.     

Feasibility of proton chemical shift imaging with a stereotactic headframe

To prove feasibility of proton chemical shift imaging ((1)H CSI) during stereotactic procedure, authors performed (1)H CSI in combination with a stereotactic headframe and selected targets according to local metabolic information, evaluated the pathologic results. The (1)H CSI directed stereotactic biopsy was performed in four patients. (1)H CSI and conventional Gd-enhancement stereotactic MRI were performed simultaneously after the fitting of a stereotactic headframe. Focal areas of increased phosphocholine(Cho)/phosphocreatine(Cr) and Lactate/Cr ratios were selected as target sites in the stereotactic MR images. (1)H CSI is possible with the stereotactic headframe in place. Pathologic samples taken from areas of increased Cho/Cr ratios and decreased NAA/Cr ratios provided information upon increased cellularity, mitoses and cellular atypism, and facilitated diagnosis. Pathologic samples taken from areas of increased Lac/Cr ratio showed predominant feature of necrosis. (1)H CSI was feasible with the stereotactic headframe in place. The final pathologic results obtained were concordant with the local metabolic information from (1)H CSI. We believe that (1)H CSI-directed stereotactic biopsy has the potential to significantly improve the accuracy of stereotactic biopsy targeting.     

Kinetics of isolated peak 5 in TLD-100 following 165°C post-irradiation annealing

Peak 5 in the glow curve of TLD-100 (at a temperature of approximately 200°C) was studied as a function of post-irradiation annealing at 165°C. Computerized glow peak analysis shows that the order of kinetics of peak 5 increases from 1.2 ± 0.05 (1 SD) following 165°C annealing for five minutes to 1.72 ± 0.07 (1 SD) following annealing at 165°C for thirty minutes. Extrapolation of the results to zero annealing time yields a value of kinetic order consistent with unity. The glow curve analysis also indicates that peak 4 (the satellite peak at approximately 175°C) is undetectable even at the lowest annealing duration of 5 minutes. The high temperature satellite of peak 5 (peak 6 at approximately 225°C) grows with increasing annealing time to 10% of the intensity of peak 5 after annealing for 30 min. Glow curve analysis including peak 6, however, does not significantly change the conclusions regarding the increase in the order of kinetics of peak 5 as a function of annealing time or the consistency of the extrapolated results with kinetic order unity at zero annealing time. Analysis of isothermal decay curves at 165°C shows that the relative intensity of peak 4 to peak 5 decreases with increasing annealing time, from 8% after 5 min annealing to 0.5% after 30 min annealing.     

Chemically deposited copper oxide thin films: structural, optical and electrical characteristics

Thin films of copper oxide with thickness ranging from 0.05–0.45 μm were deposited on microscope glass slides by successively dipping them for 20 s each in a solution of 1 M NaOH and then in a solution of copper complex. Temperature of the NaOH solution was varied from 50–90°C, while that of the copper solution was maintained at room temperature. X-ray diffraction patterns showed that the films, as prepared, are of cuprite structure with composition Cu₂O. Annealing the films in air at 350°C converts these films to CuO. This conversion is accompanied by a shift in the optical band gap from 2.1 eV (direct) to 1.75 eV (direct). The films show p-type conductivity, 5×10⁻⁴ Ω⁻¹ cm⁻¹ for a film of thickness 0.15 μm. Electrical conductivity of this film increases by a factor of 3 when illuminated with 1 kW m⁻² tungsten halogen radiation. Annealing in a nitrogen atmosphere at temperatures up to 400°C does not change the composition of the films. However, the conductivity in the dark as well as the photoconductivity of the film increases by an order of magnitude. The electrical conductivity of the CuO thin films produced by air annealing at 400°C, is high, 7×10⁻³ Ω⁻¹ cm⁻¹. These films are also photoconductive.     

Buffers for high temperature superconductor coatings. Low temperature growth of CeO2 films by metal–organic chemical vapor deposition and their implementation as buffers

Smooth, epitaxial cerium dioxide thin films have been grown in-situ in the 450–650°C temperature range on (001) yttria-stabilized zirconia (YSZ) substrates by metal–organic chemical vapor deposition (MOCVD) using a new fluorine-free liquid Ce precursor. As assessed by X-ray diffraction, transmission electron microscopy (TEM), and high-resolution electron microscopy (HREM), the epitaxial films exhibit a columnar microstructure with atomically abrupt film-substrate interfaces and with only minor bending of the crystal plane parallel to the substrate surface near the interface and at the column boundaries. With fixed precursor temperature and gas flow rate, the CeO₂ growth rate decreases from 10 Å/min at 450°C to 6.5 Å/min at 540°C. The root-mean-square roughness of the films also decreases from 15.5 Å at 450°C to 4.3 Å at 540°C. High-quality, epitaxial YBa₂C₃O_7−x films have been successfully deposited on these MOCVD-derived CeO₂ films grown at temperatures as low as 540°C. They exhibit T_c=86.5 K and J_c=1.08×10⁶ A/cm² at 77.4 K.     

Ellipsometric spectroscopy study of photoluminescent Si/SiO2 systems obtained by magnetron co-sputtering

Si nanograins embedded in silica matrix were obtained by magnetron cosputtering of both Si and SiO₂ at different substrate temperature (200–700°C) and thermal annealing at 1100°C. The samples were characterized by ellipsometric spectroscopy, high-resolution electron microscopy observations and photoluminescence. The highest excess of Si atoms was found to be incorporated for deposition temperature near 400–500°C, giving rise to a maximum PL and a shift of the peak position towards lower energy. These features might be interpreted in terms of quantum size effects and of density of grains, even though the interface states seem to be involved in the improvement of the photoluminescence efficiency.     

Selective F MR imaging of 5-fluorouracil and α-fluoro-β-alanine

A ¹⁹F MR chemical shift imaging (CSI) technique is presented which enables selective imaging of the antineoplastic drug 5-fluorouracil (5-FU) and its major catabolite α-fluoro-β-alanine (FBAL). The CSI sequence employs a chemical shift selective (CHESS) saturation pulse to suppress either the 5-FU or the FBAL resonance before the other component of the two-line ¹⁹F MR spectrum is measured. Because the transmitter frequency can always be set to the Larmor frequency of the ¹⁹F resonance to be imaged, this approach yields 5-FU and FBAL MR images free of chemical shift artifacts in read-out and slice-selection direction. In phantom experiments, selective 5-FU and FBAL images with a spatial resolution of 15 × 15 × 20 mm³ (4.5 ml) were obtained in 30 min from a model solution, whose drug and catabolite concentrations were similar to those estimated in the liver of tumor patients undergoing IV chemotherapy with 5-FU. The drug-specific MR imaging technique developed is, therefore, well-suited for the direct and noninvasive monitoring of the up-take and trapping of 5-FU in liver tumors in vivo.     

Reversible H2 passivation of Si ≡ Si3 interface defects in (1 1 1)Si/SiO2

K-band electron spin resonance (ESR) at 4.3 K has revealed the dipole-dipole (DD) interaction effects between [1 1 1]P_b centers (^*Si ≡ Si₃ defects with unpaired sp³ hybrid [1 1 1]) at the 2 dimensional (1 1 1)Si/SiO₂ interface. This has been enabled by the perfectly reversible H₂ passivation of P_b, which affects the defect's spin state. Sequential hydrogenation at 253–353°C and degassing treatments in high vacuum at 743–835°C allowed to vary the P_b density in the range 5 × 10¹⁰ < [P_b] (1.14 ± 0.06) × 10¹³ cm^-2. With increasing [P_b] fine structure doublets are clearly resolved. It is found that (1 1 1)Si/SiO₂ interfaces, dry thermally grown at ≈920°C, naturally comprise a ^*Si ≡ Si₃ defect density — passivated or not — of 1.14 × 10¹³ cm^-2.