PubMed · 4495597
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1974. Radio-active danger.. https://pubmed.ncbi.nlm.nih.gov/4495597/
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Owing to the high radiation exposure associated with computed tomography (CT) examinations and the image quality degradation caused by conventional radiation shielding materials, this study evaluated the dose reduction performance and image quality maintenance potential of a newly developed lead-free composite shielding material. This material was composed of bismuth, tungsten, tungsten carbide, aluminium, and polyurethane. Phantom-based dose measurements demonstrated that the shielding material achieved dose reduction rates ranging from 17.6% to 37.6%, depending on tube voltage. Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and changes in tube current-time product (mAs) under a scout-based automatic exposure control (AEC) protocol were analysed according to the presence or absence of the shielding material across regions. For the clinical evaluation, CT scans were performed on four patients. Furthermore, the images were reviewed to evaluate whether this material affected image quality. The shielding material exhibited radiation reduction levels comparable to those reported in previous studies. SNR and CNR analyses showed minor statistical variations in certain regions; however, most differences were not statistically significant, and even significant differences remained within a range that did not compromise diagnostic image quality. Under the scout-based AEC protocol, the use of the shielding material resulted in less than 1% variation in mAs values. No visually perceptible artefacts or clinically significant image quality degradation were observed. The proposed composite shielding material demonstrated the potential to mitigate some limitations of conventional shielding materials and showed preliminary clinical feasibility as an adjunctive strategy for radiation dose reduction in CT examinations.
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Due to a large variety of sunscreens, it is important to study among other things, the effect of the vehicle on the thickness and uniformity of sunscreen films. In this study, we determined the physical stability of five sunscreens SPF 15 (FA to FG), containing or not PVP/eicosene crosspolymer (PVP/EC), and two different self-emulsifying bases (SEB), and also evaluated the influence of the vehicle in their SPF. In the study of physical stability, formulations were stored at 25, 37 and 45 degrees C, for 28 days. Viscosity and rheological behavior of the formulations were determined using a Brookfield rheometer. Investigations of the SPF were carried out in a group of 30 volunteers (COLIPA methodology). The FC samples (phosphate-based SEB), with a lower thixotropy, showed statistically higher SPF (13.6) when compared with FB (non-ionic SEB), which presented higher thixotropy and a SPF of 9.84. The FE sample (phosphate-based SEB+PVP/EC) presented the same SPF as the FC, but had a higher thixotropy. The FB formulation (stable with higher thixotropy) showed the lowest SPF while FC (an unstable formulation with lower thixotropy) presented a higher SPF. We concluded that FE was the best formulation showing a higher SPF and stability and the study of rheology can help the development of sunscreens.