BACKGROUND AND PURPOSE:Little has been known about the clinical and angiographic follow-up results of stent-only therapy for intracranial vertebrobasilar dissecting aneurysms (VBDA). The purpose of this study was to evaluate the feasibility, safety, clinical, and angiographic follow-up of stent-only therapy for VBDA.
. Diagnostic accuracy and interobserver variability of pulsed arterial spin labeling for glioma grading. Acta Radiol 2008;49:450Á457.Background: Although pulsed arterial spin labeling (PASL) enables the reliable qualitative grading of brain tumors, its use in quantification for glioma grading may be hampered by the limited interobserver variability associated with low spatial resolution. Purpose: To assess the interobserver variability and diagnostic accuracy of the relative tumor perfusion signal intensity (rTPS) calculated using PASL in glioma grading. Material and Methods: Fifty-eight patients with 61 cerebral astrocytomas underwent conventional MR imaging and PASL. Receiver operating characteristic analyses were used to determine the optimum thresholds for tumor grading. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for identifying highgrade gliomas were also calculated. Cohen's k statistic was used to determine the levels of interobserver variability in the quantitative analysis of PASL. Results: The sensitivity, specificity, PPV, and NPV for determining a high-grade glioma with conventional MR imaging were 77.1, 73.1, 79.4, and 70.4%, respectively. A threshold value of 1.28 for rTPS provided a sensitivity, specificity, PPV, and NPV of 82.9, 96.2, 96.7, and 80.6%, respectively. There was a statistically significant difference in the rTPS between low-and high-grade astrocytomas (1.14 vs. 1.47, P B0.05). In the interobserver variability analysis, substantial agreement was obtained for the quantitative rTPS measurement from PASL (k 00.72). Conclusion: Quantitative perfusion measurement with PASL can improve the diagnostic accuracy of preoperative glioma grading, as compared to the application of conventional imaging alone. However, the interobserver variability for quantification is substantial.
BACKGROUND AND PURPOSE:Although coiling has been favorably comparable with clipping for treatment of most intracranial aneurysms, there is a controversy on which modality is safer for anterior choroidal artery (AchoA) aneurysm. We retrospectively evaluated the clinical outcomes and treatmentrelated complications after surgical clipping and endovascular coiling of AchoA aneurysms.
Errors are examined in determining the refractive index and thickness of very thin SiO2 films on c-Si substrates as measured with the commonly used rotating analyzer ellipsometer. Systematic errors in the ellipsometric parameters Δ, ψ, δΔ, and δψ are calculated from the experimental hardware errors. Random errors are measured. The propagation of errors from δΔ and δψ to errors in refractive index (n) and film thickness (d), δn and δd, are calculated for oxide thicknesses from 30 to 200 Å. It is verified that the thinner the oxide is and the lower the photon energy where c-Si becomes less absorbing, the larger the errors become. A minimum error of δn and δd is observed at the spectral region of 3.6–4.0 eV and around 5.2 eV. From the reported results for a high precision ellipsometer, judgments are made about the value of the extracted parameters for thin films, and recommendations are offered to minimize the errors.
With the increasing demand of the cost effective optical recording system, the optical media based on the phase-change phenomena have attracted an extensive research interest. One of the commonly used recording material for the phase-change optical disk is Ge-Sb-Te (GST) alloys which show a reversible phase transformation between the crystalline and the amorphous, thus the corresponding reflectivity change.[1,2] It has been reported that GST-alloys near to the stoichiometric compound are suitable for high speed application while other alloys like In-Sb-Te and Ag-In-Sh-Te are reported to be appropriate for low -speed applications.[3,4] The main purpose of this research is to study the feasibility of GST-alloys for the blue wavelength region for both high density recording and linear velocity applications. Variation of the complex refractive indices with Sb-addition in GST-alloy and their wavelength dependence were studied in the present research by using spectroscopic ellipsometry (SE) and atomic force microscopy (AFM). The reflectivity spectra of GST with different chemical compositions were calculated using these optical constants, and compared with the measured spectra.
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