Browsing by Author "Lewis, S"

Now showing 1 - 4 of 4
  • No Thumbnail Available
    Item
    Comparison of propagation-based phase-contrast CT and absorption-based CT for breast imaging using synchrotron radiation
    (Society of Photo-Optical Instrumentation Engineers (SPIE), 2020-05-22) Taba, ST; Lewis, S; Baran, PM; Arhatari, BD; Nesterets, YI; Mayo, SC; Thompson, D; Fox, J; Kumar, B; Prodanovic, Z; Häusermann, D; Masimenko, A; Hall, CJ; Dimmock, M; Pavlov, KM; Peele, AG; Quiney, HM; Lockie, D; Tromba, G; Gureyev, TE; Brennan, PC
    Propagation-based phase-contrast CT (PB-CT) is a novel imaging technique that visualises variations in both X-ray attenuation and refraction. This study aimed to compare the clinical image quality of breast PB-CT using synchrotron radiation with conventional absorption-based CT (AB-CT), at the same radiation dose. Seven breast mastectomy specimens were scanned and evaluated by a group of 14 radiologists and medical imaging experts who assessed the images based on seven radiological image quality criteria. Visual grading characteristics (VGC) were used to analyse the results and the area under the VGC curve was obtained to measure the differences between the two techniques. For six image quality criteria (overall quality, perceptible contrast, lesion sharpness, normal tissue interfaces, calcification visibility and image noise), PB-CT images were superior to AB-CT images of the same dose (AUCVGC: 0.704 to 0.914, P≤.05). For the seventh criteria (artefacts), PB-CT images were also rated better than AB-CT images (AUCVGC: 0.647) but the difference was not significant. The results of this study provide a solid basis for future experimental and clinical protocols of breast PB-CT. © 2020 Society of Photo-Optical Instrumentation Engineers (SPIE).
  • No Thumbnail Available
    Item
    Energy optimisation of propagation-based phase-contrast computed tomography: a quantitative image quality assessment
    (SPIE, 2022-04-04) Lim, B; Lewis, S; Arhatari, BD; Nesterets, YI; Mayo, SC; Fox, J; Thomposon, D; Kumar, B; Häusermann, D; Maksimenko, A; Hall, CJ; Dimmock, M; Lockie, D; Rickard, M; Giannoitti, N; Peele, AG; Quiney, HM; Gureyev, TE; Brennan, PC; Taba, ST
    Purpose: This study aims at establishing the optimum x-ray energy for synchrotron acquired propagation-based computed tomography (PB-CT) images to obtain highest radiological image quality of breast mastectomy samples. It also examines the correlation between objective physical measures of image quality with subjective human observer scores to model factors impacting visual determinants of image quality. Approach: Thirty mastectomy samples were scanned at Australian Synchrotron’s Imaging and Medical Beamline. Samples were scanned at energies of 26, 28, 30, 32, 34, and 60 keV at a standard dose of 4mGy. Objective physical measures of image quality were assessed using signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), SNR/resolution (SNR/res), CNR/resolution (CNR/res) and visibility. Additional calculations for each measure were performed against reference absorption-based computer tomography (AB-CT) images scanned at 32 keV and 4mGy. This included differences in SNR (dSNR), CNR (dCNR), SNR/res (dSNR/res), CNR/res (dCNR/res), and visibility (dVis). Physical measures of image quality were also compared with visual grading analysis data to determine a correlation between observer scores and objective metrics. Results: For dSNR, dCNR, dSNR/res, dCNR/res, and dVis, a statistically significant difference was found between the energy levels. The peak x-ray energy for dSNR and dSNR/res was 60 keV. For dCNR and dCNR/res 34 keV produced the highest measure compared to 28 keV for dVis. Visibility and CNR correlate to 56.8% of observer scores. Conclusion: The optimal x-ray energy differs for different objective measures of image quality with 30-34 keV providing optimum image quality for breast PB-CT. Visibility and CNR correlate highest to medical imaging expert scores. © (2022) Society of Photo-Optical Instrumentation Engineers (SPIE).
  • No Thumbnail Available
    Item
    High-resolution stalagmite reconstructions for Australian-Indonesian monsson rainfall variability during Heinrich stadial 3 and Greenland interstadial 4
    (Elsevier, 2011-02-15) Lewis, S; Gagan, MK; Ayliffe, LK; Zhao, JX; Hantoro, WS; Treble, PC; Hellstrom, JC; LeGrande, AN; Kelley, M; Schmidt, GA; Suwargadi, BW
    Little is known about the possible teleconnections between abrupt climatic changes originating in the North Atlantic and precipitation dynamics in the Australian-Indonesian summer monsoon (AISM) domain. We examine the climatic impacts of Heinrich stadial 3 (HS3) and Greenland interstadials 4 and 3 (GIS4/3) on AISM-associated precipitation through a high-resolution analysis of stable isotope (delta(18)O, delta(13)C) and trace element (Mg/Ca, P/Ca) ratios in a stalagmite from Liang Luar cave, Flores, Indonesia. Sixteen high precision (230)Th dates indicate that stalagmite LR07-E1 grew rapidly (similar to 0.3-1.0 mm/yr) in two phases between similar to 31.5-30.1 ka and similar to 27.8-25.6 ka, separated by a similar to 2.3 kyr unconformity. Temporally consistent abrupt responses occur in the Flores record during HS3 and GIS4, which are coherent with changes in stalagmite delta(18)O records from China and Brazil. The response of low-latitude precipitation to HS3 cooling and GIS4 warming, as demonstrated by the widely separated sites, comprises three distinct simplified phases: (1) a strong southward migration of the ITCZ during HS3 is associated with a decrease in rainfall at Liang Luar cave and in China, while wetter conditions are reconstructed from Brazil, (2) represents the peak of HS3 impacts and an extended hiatus begins in the Flores record and (3) where suggested dry conditions at Liang Luar throughout GIS4 form part of a coherent north-south anti-phasing in precipitation changes. The reconstructed changes are also broadly consistent with NASA GISS ModelE-R simulations of a Heinrich-like freshwater perturbation in the North Atlantic basin, which produces a southward shift in the ITCZ. The relationship between the palaeoclimate records indicates that atmospheric teleconnections rapidly propagate and synchronise climate change across the hemispheres during periods of abrupt climate change. Our findings augment recent proposals that large-scale atmospheric re-organisations during stadials and interstadials play a key role in driving changes in atmospheric CO(2) concentration, air temperature and global climate change. (C) 2011 Elsevier B.V.
  • Thumbnail Image
    Item
    Significance of the connection between bedrock, alluvium and streams: a spatial and temporal hydrogeological and hydrogeochemical assessment from Queensland, Australia
    (Elsevier B. V., 2019-02) Raiber, M; Lewis, S; Cendón, DI; Cui, T; Cox, ME; Gilfedder, M; Rassam, DW
    Catchment-scale hydrological and hydrogeological investigations commonly conclude by finding that particular stream reaches are either gaining or losing; they also often assume that the influence of bedrock aquifers on catchment water balances and water quality is insignificant. However, in many cases, such broad findings are likely to oversimplify the spatial and temporal complexity of the connections between the different hydrological system components, particularly in regions dominated by cycles of droughts and flooding. From a modelling perspective, such oversimplifications can have serious implications on the process of identifying the magnitude and direction of the exchange fluxes between the surface and groundwater systems. In this study, we use 3D geological modelling and historic water chemistry and hydraulic records to identify the origins of groundwater at different locations in the alluvium and along the course of streams in the Lockyer Valley (Queensland, Australia), a catchment impacted by a severe drought (‘Millennium Drought’) from 1998 to 2009, followed by extensive flooding in 2011. We also demonstrate how discharge from the sub-alluvial regional-scale volcanic and sedimentary bedrock influences the water balance and water quality of the alluvium and streams. The investigation of aquifer geometry via development of a three-dimensional geological model combined with an assessment of hydraulic data provided important insights on groundwater flow paths and helped to identify areas where bedrock aquifers interact with shallow alluvial aquifers and streams. Multivariate statistical techniques were then applied as an additional line of evidence to groundwater and surface water hydrochemical data from large historical datasets. This confirmed that most sub-catchments within the Lockyer Valley have distinct water chemistry patterns, which result from mixing of different water sources, including discharge from the sub-alluvial bedrock. Importantly, in addition to the observed spatial variability, time-series hydrochemical groundwater and surface water data further demonstrated that the hydraulic connection between alluvial aquifers, streams and sub-alluvial bedrock aquifers is temporally dynamic with very significant changes occurring at the transition from normal to drought conditions and following flooding, affecting both catchment water quality and water balances. Crown Copyright © 2018 Published by Elsevier B.V.