55 research outputs found
Tenfold your photons -- a physically-sound approach to filtering-based variance reduction of Monte-Carlo-simulated dose distributions
X-ray dose constantly gains interest in the interventional suite. With dose
being generally difficult to monitor reliably, fast computational methods are
desirable. A major drawback of the gold standard based on Monte Carlo (MC)
methods is its computational complexity. Besides common variance reduction
techniques, filter approaches are often applied to achieve conclusive results
within a fraction of time. Inspired by these methods, we propose a novel
approach. We down-sample the target volume based on the fraction of mass,
simulate the imaging situation, and then revert the down-sampling. To this end,
the dose is weighted by the mass energy absorption, up-sampled, and distributed
using a guided filter. Eventually, the weighting is inverted resulting in
accurate high resolution dose distributions. The approach has the potential to
considerably speed-up MC simulations since less photons and boundary checks are
necessary. First experiments substantiate these assumptions. We achieve a
median accuracy of 96.7 % to 97.4 % of the dose estimation with the proposed
method and a down-sampling factor of 8 and 4, respectively. While maintaining a
high accuracy, the proposed method provides for a tenfold speed-up. The overall
findings suggest the conclusion that the proposed method has the potential to
allow for further efficiency.Comment: 6 pages, 3 figures, Bildverarbeitung f\"ur die Medizin 202
The role of the regulatory framework for innovation activities: The EU ETS and the German paper industry
Based on a research framework which combines environmental economics and innovation studies, we explore the relevance of the regulatory framework for innovation activities in the German paper industry, with a focus on climate poli-cies. Innovation activities considered include research and development, adop-tion and organizational change. Empirically, we mainly rely on the survey data of paper producers and technology providers. Findings suggest that innovation activities are mainly governed by market factors and (as yet) are hardly affected by the European Emission Trading System and other climate policies. Also, the impact of these policies on innovation activities is lower for technology providers than for paper producers. However, the majority of companies expect the ef-fects of the regulatory climate policy framework on innovation to increase by 2020. --
Effects of Tissue Material Properties on X-Ray Image, Scatter and Patient Dose Determined using Monte Carlo Simulations
With increasing patient and staff X-ray radiation awareness, many efforts
have been made to develop accurate patient dose estimation methods. To date,
Monte Carlo (MC) simulations are considered golden standard to simulate the
interaction of X-ray radiation with matter. However, sensitivity of MC
simulation results to variations in the experimental or clinical setup of image
guided interventional procedures are only limited studied. In particular, the
impact of patient material compositions is poorly investigated. This is mainly
due to the fact, that these methods are commonly validated in phantom studies
utilizing a single anthropomorphic phantom. In this study, we therefore
investigate the impact of patient material parameters mapping on the outcome of
MC X-ray dose simulations. A computation phantom geometry is constructed and
three different commonly used material composition mappings are applied. We
used the MC toolkit Geant4 to simulate X-ray radiation in an interventional
setup and compared the differences in dose deposition, scatter distributions
and resulting X-ray images. The evaluation shows a discrepancy between
different material composition mapping up to 20 % concerning directly
irradiated organs. These results highlight the need for standardization of
material composition mapping for MC simulations in a clinical setup.Comment: 6 pages, 4 figures, Bildverarbeitung f\"ur die Medizin 201
Fully-automatic CT data preparation for interventional X-ray skin dose simulation
Recently, deep learning (DL) found its way to interventional X-ray skin dose
estimation. While its performance was found to be acceptable, even more
accurate results could be achieved if more data sets were available for
training. One possibility is to turn to computed tomography (CT) data sets.
Typically, computed tomography (CT) scans can be mapped to tissue labels and
mass densities to obtain training data. However, care has to be taken to make
sure that the different clinical settings are properly accounted for. First,
the interventional environment is characterized by wide variety of table setups
that are significantly different from the typical patient tables used in
conventional CT. This cannot be ignored, since tables play a crucial role in
sound skin dose estimation in an interventional setup, e. g., when the X-ray
source is directly underneath a patient (posterior-anterior view). Second, due
to interpolation errors, most CT scans do not facilitate a clean segmentation
of the skin border. As a solution to these problems, we applied connected
component labeling (CCL) and Canny edge detection to (a) robustly separate the
patient from the table and (b) to identify the outermost skin layer. Our
results show that these extensions enable fully-automatic, generalized
pre-processing of CT scans for further simulation of both skin dose and
corresponding X-ray projections.Comment: 6 pages, 4 figures, Bildverarbeitung f\"ur die Medizin 2020, code
will be accessible soon (url
New genetic loci link adipose and insulin biology to body fat distribution.
Body fat distribution is a heritable trait and a well-established predictor of adverse metabolic outcomes, independent of overall adiposity. To increase our understanding of the genetic basis of body fat distribution and its molecular links to cardiometabolic traits, here we conduct genome-wide association meta-analyses of traits related to waist and hip circumferences in up to 224,459 individuals. We identify 49 loci (33 new) associated with waist-to-hip ratio adjusted for body mass index (BMI), and an additional 19 loci newly associated with related waist and hip circumference measures (P < 5 × 10(-8)). In total, 20 of the 49 waist-to-hip ratio adjusted for BMI loci show significant sexual dimorphism, 19 of which display a stronger effect in women. The identified loci were enriched for genes expressed in adipose tissue and for putative regulatory elements in adipocytes. Pathway analyses implicated adipogenesis, angiogenesis, transcriptional regulation and insulin resistance as processes affecting fat distribution, providing insight into potential pathophysiological mechanisms
The Science Case for Multi-Object Spectroscopy on the European ELT
This White Paper presents the scientific motivations for a multi-object
spectrograph (MOS) on the European Extremely Large Telescope (E-ELT). The MOS
case draws on all fields of contemporary astronomy, from extra-solar planets,
to the study of the halo of the Milky Way and its satellites, and from resolved
stellar populations in nearby galaxies out to observations of the earliest
'first-light' structures in the partially-reionised Universe. The material
presented here results from thorough discussions within the community over the
past four years, building on the past competitive studies to agree a common
strategy toward realising a MOS capability on the E-ELT. The cases have been
distilled to a set of common requirements which will be used to define the
MOSAIC instrument, entailing two observational modes ('high multiplex' and
'high definition'). When combined with the unprecedented sensitivity of the
E-ELT, MOSAIC will be the world's leading MOS facility. In analysing the
requirements we also identify a high-multiplex MOS for the longer-term plans
for the E-ELT, with an even greater multiplex (>1000 targets) to enable studies
of large-scale structures in the high-redshift Universe. Following the green
light for the construction of the E-ELT the MOS community, structured through
the MOSAIC consortium, is eager to realise a MOS on the E-ELT as soon as
possible. We argue that several of the most compelling cases for ELT science,
in highly competitive areas of modern astronomy, demand such a capability. For
example, MOS observations in the early stages of E-ELT operations will be
essential for follow-up of sources identified by the James Webb Space Telescope
(JWST). In particular, multi-object adaptive optics and accurate sky
subtraction with fibres have both recently been demonstrated on sky, making
fast-track development of MOSAIC feasible.Comment: Significantly expanded and updated version of previous ELT-MOS White
Paper, so there is some textual overlap with arXiv:1303.002
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