National Nuclear Energy Commission

About: National Nuclear Energy Commission is a government organization based out in Rio de Janeiro, Brazil. It is known for research contribution in the topics: Dosimetry & Laser. The organization has 3816 authors who have published 4694 publications receiving 59951 citations.

Properties of porous silica glasses prepared via sol-gel process

Abstract: Porous silica glasses were obtained through sol–gel processing employing tetramethylorthosilicate (TMOS) as precursor, with HNO3 and HF as catalysts. The gels were heat-treated at temperatures ranging from 400°C to 900°C. Some gels were γ-ray irradiated. Specific surface areas, pore size distributions and solid densities of the gels were obtained by nitrogen sorption and mercury pycnometry. Pore morphology was inferred through curves of nitrogen sorption hysteresis, and an evaluation of pore connectivities and permeabilities were carried out. The shape of the isotherms of gels submitted to different heat treatments was attributed to pores of cylindrical shape. The average pore size was controlled by the HF concentration. The average pore size distribution of gels irradiated with γ-rays decreased. We measured the properties of porous glasses when immersed in aqueous solution containing cesium chloride. Porous silica glasses heat-treated at temperatures above 650°C did not fracture when immersed in aqueous solutions with CsCl.

Controlling for Artifacts in Widefield Optical Coherence Tomography Angiography Measurements of Non-Perfusion Area.

Abstract: The recent clinical adoption of optical coherence tomography (OCT) angiography (OCTA) has enabled non-invasive, volumetric visualization of ocular vasculature at micron-scale resolutions. Initially limited to 3 mm × 3 mm and 6 mm × 6 mm fields-of-view (FOV), commercial OCTA systems now offer 12 mm × 12 mm, or larger, imaging fields. While larger FOVs promise a more complete visualization of retinal disease, they also introduce new challenges to the accurate and reliable interpretation of OCTA data. In particular, because of vignetting, wide-field imaging increases occurrence of low-OCT-signal artifacts, which leads to thresholding and/or segmentation artifacts, complicating OCTA analysis. This study presents theoretical and case-based descriptions of the causes and effects of low-OCT-signal artifacts. Through these descriptions, we demonstrate that OCTA data interpretation can be ambiguous if performed without consulting corresponding OCT data. Furthermore, using wide-field non-perfusion analysis in diabetic retinopathy as a model widefield OCTA usage-case, we show how qualitative and quantitative analysis can be confounded by low-OCT-signal artifacts. Based on these results, we suggest methods and best-practices for preventing and managing low-OCT-signal artifacts, thereby reducing errors in OCTA quantitative analysis of non-perfusion and improving reproducibility. These methods promise to be especially important for longitudinal studies detecting progression and response to therapy.