Browsing by Author "Santiago, A."
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- 10 kVp rule - An anthropomorphic pelvis phantom imaging study using a CR system: impact on image quality and effective dose using AEC and manual modePublication . Lança, Luís; Franco, L.; Ahmed, A.; Harderwijk, M.; Nasir, S.; Ndlovu, J.; Oliveira, M.; Santiago, A.; Hogg, PeterPurpose: This study aims to investigate the influence of tube potential (kVp) variation in relation to perceptual image quality and effective dose for pelvis using automatic exposure control (AEC) and non-AEC in a computed radiography (CR) system. Methods and Materials: To determine the effects of using AEC and non-AEC by applying the 10 kVp rule in two experiments using an anthropomorphic pelvis phantom. Images were acquired using 10 kVp increments (60-120 kVp) for both experiments. The first experiment, based on seven AEC combinations, produced 49 images. The mean mAs from each kVp increment were used as a baseline for the second experiment producing 35 images. A total of 84 images were produced and a panel of 5 experienced observers participated for the image scoring using the 2 AFC visual grading software. PCXMC software was used to estimate the effective dose. Results: A decrease in perceptual image quality as the kVp increases was observed both in non-AEC and AEC experiments, however no significant statistical differences (p> 0.05) were found. Image quality scores from all observers at 10 kVp increments for all mAs values using non-AEC mode demonstrates a better score up to 90 kVp. Effective dose results show a statistical significant decrease (p=0.000) on the 75th quartile from 0.3 mSv at 60 kVp to 0.1 mSv at 120 kVp when applying the 10 kVp rule in non-AEC mode. Conclusion: No significant reduction in perceptual image quality is observed when increasing kVp whilst a marked and significant effective dose reduction is observed.
- 10 kVp rule – An anthropomorphic pelvis phantom imaging study using a CR system: impact on image quality and effective dose using AEC and manual modePublication . Lança, Luís; Franco, L.; Ahmed, A.; Harderwijk, M.; Marti, C.; Nasir, S.; Ndlovu, J.; Oliveira, M.; Santiago, A.; Hogg, PeterBackground - Pelvis and hip radiography are consistently found to be amongst the highest contributors to the collective effective dose (E) in all ten DOSE DATAMED countries in Europe, representing 2.8 to 9.4% of total collective dose (S) in the TOP 20 exams list. The level of image quality should provide all the diagnostic information in order not to jeopardise the diagnosis, but being able to provide the needed clinical information with the minimum dose. A recent study suggests further research to determine whether the “10 kVp rule” would have value for a range of examinations using Computed Radiography (CR) systems. As a “rule of thumb” increasing the kVp by 10 whilst halving the mAs is suggested to give a similar perceptual image quality when compared to the original exposure factors. Aims - In light of the 10kVp rule, this study aims to investigate the influence of tube potential (kVp) variation in relation to perceptual image quality and E for pelvis imaging using automatic exposure control (AEC) and non-AEC in a Computed Radiography (CR) system. Research questions - Does the 10kVp rule works for the pelvis in relation to image quality in a CR system? Does the image quality differs when the AEC is used instead of manual mode using the 10kVp rule and how this impacts on E?
- Tensile properties of S355 butt welds after exposure to high temperaturesPublication . Rodrigues, D. M.; Leitao, Carlos; Balakrishnan, M.; Craveiro, Hélder D.; Santiago, A.The influence of the exposure to high temperatures on the tensile properties and failure mode of butt-welded connections in 5355 J2 steel was assessed. With this aim, welds were produced using GMAW and FCAW semiautomatic processes. Transverse tensile specimens were extracted from the welded coupons, heated to high temperatures (300, 600 and 900 degrees C), cooled to room temperature and then loaded to failure. Microstructural characterization and hardness measurements were performed to explain the tensile behaviour of the specimens after exposure to high temperatures. Tests at ambient temperature were also conducted for benchmark comparison. From the analyses, it was possible to conclude that, in the absence of welding defects, the residual properties of the 5355 joints, after heat exposure, are very similar to that of the base material. However, the presence of welding defects, depending on its severity and typology, may conduct to rupture in the welds and low residual strength, after heat exposure. This happens even if those defects not affect the tensile properties of the connections in the as-welded condition. The residual capacity of steel structures will be only severely reduced after heat exposure to temperatures in the eutectoid range, i.e., between 700 and 900 degrees C. The critical exposure temperature may vary according to the chemical composition of the steels/welds and to the duration of the heat exposure. The strength loss and the ductility of the BM and of the connections are dependent of the duration of the heat exposure. Very long exposure conditions conduct to a maximum decrease in residual yield and ultimate strength of 30 % and 20%, respectively, in S355 J2 steels and welds.