131 research outputs found
Quantitative Effect of Metal Artefact Reduction on CT-based attenuation correction in FDG PET/CT in patients with hip prosthesis
No full textAbstract Background Metal artefact reduction (MAR) techniques still are in limited use in positron emission tomography/computed tomography (PET/CT). This study aimed to investigate the effect of Smart MAR on quantitative PET analysis in the vicinity of hip prostheses. Materials and methods Activities were measured on PET/CT images in 6 sources with tenfold activity concentration contrast to background, attached to the head, neck and the major trochanter of a human cadaveric femur, and in the same sources in similar locations after a hip prosthesis (titanium cup, ceramic head, chrome-cobalt stem) had been inserted into the femur. Measurements were compared between PET attenuation corrected using either conventional or MAR CT. In 38 patients harbouring 49 hip prostheses, standardized uptake values (SUV) in 6 periprosthetic regions and the bladder were compared between PET attenuation corrected with either conventional or MAR CT. Results Using conventional CT, measured activity decreased with 2 to 13% when the prosthesis was inserted. Use of MAR CT increased measured activity by up to 11% compared with conventional CT and reduced the relative difference with the reference values to under 5% in all sources. In all regions, to the exception of the prosthesis shaft, SUVmean increased significantly (p < 0.001) by use of MAR CT. Median (interquartile range) percentual increases of SUVmean were 1.4 (0.0–4.2), 4.0 (1.8–7.8), 7.8 (4.1–12.4), 1.5 (0.0–3.2), 1.4 (0.8–2.8) in acetabulum, lateral neck, medial neck, lateral diaphysis and medial diaphysis, respectively. Except for the shaft, the coefficient of variation did not increase significantly. Except for the erratic changes in the prosthesis shaft, decreases in SUVmean were rare and small. Bladder SUVmean increased by 0.9% in patients with unilateral prosthesis and by 4.1% in patients with bilateral prosthesis. Conclusions In a realistic hip prosthesis phantom, Smart MAR restores quantitative accuracy by recovering counts in underestimated sources. In patient studies, Smart MAR increases SUV in all areas surrounding the prosthesis, most markedly in the femoral neck region. This proves that underestimation of activity in the PET image is the most prevalent effect due to metal artefacts in the CT image in patients with hip prostheses. Smart MAR increases SUV in the urinary bladder, indicating effects at a distance from the prosthesis
A data driven gully head susceptibility map of Africa at 30 m resolution
No full textPredicting gully erosion at the continental scale is challenging with current generation models. Moreover, datasets reflecting gully erosion processes are still rather scarce, especially in Africa. This study aims to bridge this gap by collecting an extensive dataset and developing a robust, empirical model that predicts gully head density at high resolution for the African continent. We developed a logistic probability model at 30 m resolution that predicts the likelihood of gully head occurrence using currently available GIS data sources. To calibrate and validate this model, we used a new database of 31,531 gully heads, mapped over 1216 sites across Africa. The exact location of all gully heads was manually mapped by trained experts using high-resolution imagery available from Google Earth. This allowed the extraction of detailed information at the gully head scale, such as the local soil surface slope. Variables included in our empirical model are topography, climate, vegetation, soil characteristics and tectonic context. They are consistent with our current process-based understanding of gully formation and evolution. The model shows that gully occurrences mainly depend on slope steepness, soil texture and vegetation cover and to a lesser extent on rainfall intensity and tectonic activity. The combination of these factors allows for robust and fairly reliable predictions of gully head occurrences, with Areas Under the Curve for validation around 0.8. Based on these results, we present the first gully head susceptibility map for Africa at a 30 m resolution.sponsorship: The authors declare the following financial interests/personal re- lationships which may be considered as potential competing interests: Sofie De Geeter reports financial support was provided by Research Foundation Flanders. Sofie De Geeter holds a PhD grant from Fonds Wetenschappelijk Onderzoek (Research Foundation Flanders - grant number: 11D6422N) . The authors thank Tim Peirs, Cuinera Isenborghs, Ward D Hoore, Rani Mertens, Marius Lambert and Laura Laforge for their contribution to the gully head density database. (Research Foundation Flanders, Fonds Wetenschappelijk Onderzoek (Research Foundation Flanders)|11D6422N)status: Published onlin
Soil erosion and sediment yield in Africa: Processes and factors
No full textAfrica experiences diverse and often intense soil erosion processes, yet the interplay between these processes and observed sediment yield (SY) at catchment scales is insufficiently understood. Building on previous continental- scale assessments, this study integrates a newly verified database of measured SY at 425 river outlets with, model-based estimates of Rill and Sheet Erosion (RSE), Landslide Mobilization Rates (LMR), and Gully Head Susceptibility (GHS). Our approach addresses a key gap in earlier work, which primarily relied on environmental predictors without explicitly quantifying the contribution of multiple geomorphic processes. Our results indicate that the mean observed SY is 6.07 t center dot ha-1 center dot yr- 1, whereas modelled RSE and LMR average 9.42 t center dot ha- 1 center dot yr- 1 and 1.51 t center dot ha- 1 center dot yr- 1, respectively. Although direct estimates of gully erosion were not available, the moderate to strong correlations between SY and both LMR (r = 0.47) and GHS (r = 0.57) underscore the importance of gullies and landslides in delivering sediment to catchment outlets. In contrast, RSE shows a weaker relationship with measured SY, suggesting that traditional RUSLE-type models may substantially over- or underestimate total sediment yield if they neglect gully erosion, landslides, and in-channel deposition processes. This study contributes novel insights into continental-scale sediment dynamics by explicitly linking observed SY to distinct geomorphic processes. Our findings highlight the need for integrated modeling frameworks that account for rill and sheet erosion, landslides, and gully erosion in order to enhance the accuracy of sediment yield predictions. Such approaches are vital for guiding land management and soil conservation strategies across Africa's diverse biophysical and climatic regions
Does the topographic threshold concept explain the initiation points of sunken lanes in the European loess belt?
No full textSunken lanes or ‘road gullies’ are a common geomorphic feature in the European loess belt. These landforms are usually created by various processes over time (water erosion, mass movements and traffic). They are important for ecology and biodiversity, for recreation and transport, as well as from a hydrological and geomorphological perspective (e.g. by enhancing the runoff and sediment connectivity of the landscape). Nonetheless, little is known about their origin and evolution. The formation of sunken lanes is typically only understood in qualitative terms, while no studies so far have provided a quantitative analysis of their initiation conditions. To address this research gap and to improve our geomorphic understanding of this landform, we investigated to what extent sunken lanes can be treated and described as a gully erosion process. More specifically, we explored to what extent their position in the landscape and their characteristics can be explained by the topographic slope-area (SA) threshold that typically controls gully initiation: S=kA^b, with k and b empirical constants. Based on field surveys and LIDAR data analyses, we determined the slope gradient of the soil surface (S) and contributing area (A) for 132 representative sunken lane heads in the Belgian loess belt and collected data on several other characteristics (position of initiation and sedimentation points, width, depth and length of each sunken lane). Our results show a very large scatter on the S and A values. Moreover, the morphological characteristics of sunken lanes (e.g. width and length) showed no clear relation with these values. However, a very weak SA-threshold relation with a low b-exponent (-0.016) and a low k-coefficient (0.022) could be identified. Overall, our results show that the formation of sunken lanes is not in line with the topographic threshold conditions that govern the initiation of gullies across different environments. The low k-coefficient and the lack of a strong correlation between initiation slope and contributing area point towards an overall higher susceptibility to the formation of sunken lanes than the formation of gullies. This supports the conclusion that not only concentrated flow detachment and transport, but especially human activities (mainly traffic erosion) play a major role in the initiation and development of sunken lanes.sponsorship: S. De Geeter received a scholarship from the University of Liege. (University of Liege)status: Published onlin
Cryogenic cooling reduces high voltage arcing between electrodes operating in a vacuum
No full textCooling to a temperature of approximately liquid nitrogen or lower, reduces arcing, or high voltage breakdown, between two closely spaced electrodes operating in a vacuum. This cooling technique can be applied to electrodes having other than hemispherical shapes
Simulating the variability of TMS responses in a speech mapping case study
No full textWhen delivered over a specific cortical site, TMS can temporarily disrupt the ongoing process in that area. This allows for mapping motor and speech-related cortical areas for preoperative evaluation with recent promising clinical outcomes [1,2].
Speech corresponds to an extended, complex, highly individualized neural network [3]. We aimed to numerically explain the observed variability of TMS responses during a speech mapping experiment, performed on a healthy, right-handed male subject following Lioumis’ approach [4]. We selected four study cases with very small differences in coil position and orientation. In one case (E) a naming error occurred, while in the other three cases (NEa,b,c) the subject appointed the object images as smoothly as without TMS. T1-weighted and diffusion-weighted MRI were acquired from the subject and post-processed to construct a realistic 2-mm resolution anisotropic head model. The induced electric field distributions were computed, with the coil configuration parameters retrieved from the neuronavigation system, using the anisotropic independent impedance method [5]. Whole brain tractography was performed using the graphical toolbox ExploreDTI [6]. 35 relevant tracts were identified in a region of interest obtained from the electric field distribution. Finally, the spatio-temporal variation of the membrane potentials along these tracts was computed for all four case using the compartmental cable equation [7], with passive and active neural components.
One tract is activated for all coil positions. Another tract is only triggered for case E. NEa induced action potentials in 13 tracts, while NEb stimulated 11 tracts and NEc only one. The calculated results are certainly sensitive to the coil specifications, confirming the observed variability in this speech mapping study. However, even though one neural tract only appears to be triggered for the error case, we do not want to draw strong conclusions from this. Further research is needed on the location and functional meaning of this tract in terms of the speech-related network and on refining the neural model with synapses and network connections.
We believe case- and subject-specific modelling is necessary to accurately capture the electromagnetic and neurophysiologic phenomena triggered by TMS, certainly when the stimulation interacts with complex neural networks that can differ significantly from person to person.
References:
[1] Krieg, S.M. et al. (2012) J. Neurosurgery, 116:994-1001.
[2] Picht, T. et al. (2013) Neurosurgery, 72:808–819.
[3] Catani, M. et al. (2005) Ann. Neurol., 57:8–16.
[4] Lioumis, P. et al. (2012) J. Neurosci. Meth., 204:349–354.
[5] De Geeter, N. et al. (2012) Phys. Med. Biol., 57:2169-2188.
[6] Leemans, A. et al. (2009) Proceedings of 17th Annual Meeting of Intl. Soc. Mag. Reson. Med.
[7] Salvador, R. (2009) Numerical modelling in transcranial magnetic stimulation. PhD thesis
A diffusion tensor-based computational model for transcranial magnetic stimulation : from macroscopic fields to neuronal membrane potentials
No full textEntrepreneurial Buyout Monitor. A clear view on investment results 2014 - outlook 2015
No full textWelcome to the second edition of the Entrepreneurial Buyout Monitor – a snapshot of the trends and challenges involved in management buyouts and buy-ins of SMEs in Belgium from a practitioner’s perspective. We captured the opinions of 169 buyout experts in Belgium – including bankers, private equity investors, mezzanine players, family offices, lawyers, brokers and M&A advisers. Overall, the results indicate the investment climate has considerably improved – as expected from last year’s edition. The outlook for 2015 remains positive. The key insights from the survey are: 1) DEAL FLOW IS INCREASING – however, with higher levels of competition and more favourable lending conditions, we’ve also seen higher multiples – especially for medium sized and larger deals. It’s tougher to achieve attractive returns, so the deal origination process is critical. 2) MORE FAVOURABLE DEBT MARKETS – overall debt multiples increased and the cost of lending significantly dropped. This was true for medium sized and larger deals. However, lending conditions continue to be challenging for smaller deals – so they may need more creative deal structures. 3) ALTERNATIVE INVESTORS BECOME MORE PROMINENT – both family offices and mezzanine investors become more active in smaller MBO/MBI transactions. 4) PRIVATE EQUITY INVESTORS NEED A CLEAR STRATEGY – they need a more focussed approach to finding opportunities for growth while cutting costs. And so they must gain a deeper understanding – and further insights into the sectors they’re targeting.BD
LE TRAITEMENT DES FRACTURES DE LA DIAPHYSE HUMERALE PAR L'EMBROCHAGE CENTRO MEDULLAIRE A MINIMA
No full textFifty six diaphyseal fractures of the humerus (all types from the simple transverse to the most comminuted one) were treated by medullary wiring with a 3 mm thick Kirschner wire. The callus was formed in 54 cases after an average of nine weeks. Function was excellent or good in 47 of 51 cases followed up after 6 mth. So the method can be advocated because of its benignity in execution and aftercare and the quality of the results.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Geomorphic controls on floodplain sediment and soil organic carbon storage in a Scottish mountain river
No full textsponsorship: This research is part of a project funded by Fonds Wetenschappelijk Onderzoek (Research Foundation Flanders application G0A6317N). Ward Swinnen holds a PhD grant from Fonds Wetenschappelijk Onderzoek (Research Foundation Flanders application 1167019N). The authors thank Yasmine Hunter, Remi Swinnen, Vincent Leenaerts, Ellen Jennen and Sofie De Geeter for their assistance during the field campaigns. We express our gratitude to Mar Lodge estate, Mar estate and Invercauld estate for the permission to access the study area. (Fonds Wetenschappelijk Onderzoek (Research Foundation Flanders)|G0A6317N, Fonds Wetenschappelijk Onderzoek (Research Foundation Flanders)|1167019N)status: Publishe
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