9,662 research outputs found
Effect of delayed acquisition times on Gadolinium-enhanced MRI of the presumably normal canine brain
A delay in imaging following intravenous contrast medium administration has been recommended to reduce misdiagnoses. However, the normal variation of contrast enhancement in dogs following a delay has not been characterized. Contrast enhanced MR imaging of 22 dogs was assessed, in terms of identification of normal anatomic structures, to investigate the variation associated with 10 minute delay between contrast medium administration and imaging. All dogs had a normal brain MR imaging study and unremarkable CSF. Specific ROIs were assessed both objectively, using computer software, and subjectively using three observers. Mean contrast enhancement greater than 10% was seen in the pituitary gland, choroid plexus, meninges, temporal muscle, trigeminal nerve and the trigeminal nerve root. Structures with an active blood-brain-barrier had minimal contrast enhancement (<6%). Enhancing structures had significantly more contrast enhancement at t=1min versus t=10min, except in temporal muscle, the trigeminal nerve and the trigeminal nerve root. Inter-observer agreement was moderate to good in favor of the initial post contrast T1w sequence. The observers found either no difference or poor agreement in identification of the non-vascular structures. Intra-observer agreement was very good with all vascular structures and most non-vascular structures. A degree of meningeal enhancement was a consistent finding. The initial acquisition had higher enhancement characteristics and observer agreement for some structures; however, contrast-to-noise was comparable in the delayed phase or not significantly different. We provide baseline references and suggest that the initial T1w post contrast sequence is preferable but not essential should a delayed post contrast T1w sequence be performed
Fermion Helicity Flip Induced by Torsion Field
We show that in theories of gravitation with torsion the helicity of fermion
particles is not conserved and we calculate the probability of spin flip, which
is related to the anti-symmetric part of affine connection. Some cosmological
consequences are discussed.Comment: 6 pages, to appear in Europhysics Letter
Distance Metric Learning using Graph Convolutional Networks: Application to Functional Brain Networks
Evaluating similarity between graphs is of major importance in several
computer vision and pattern recognition problems, where graph representations
are often used to model objects or interactions between elements. The choice of
a distance or similarity metric is, however, not trivial and can be highly
dependent on the application at hand. In this work, we propose a novel metric
learning method to evaluate distance between graphs that leverages the power of
convolutional neural networks, while exploiting concepts from spectral graph
theory to allow these operations on irregular graphs. We demonstrate the
potential of our method in the field of connectomics, where neuronal pathways
or functional connections between brain regions are commonly modelled as
graphs. In this problem, the definition of an appropriate graph similarity
function is critical to unveil patterns of disruptions associated with certain
brain disorders. Experimental results on the ABIDE dataset show that our method
can learn a graph similarity metric tailored for a clinical application,
improving the performance of a simple k-nn classifier by 11.9% compared to a
traditional distance metric.Comment: International Conference on Medical Image Computing and
Computer-Assisted Interventions (MICCAI) 201
Effects of a torsion field on Big Bang nucleosynthesis
In this paper it is investigated whether torsion, which arises naturally in
most theories of quantum gravity, has observable implications for the Big Bang
nucleosynthesis. Torsion can lead to spin flips amongst neutrinos thus turning
them into sterile neutrinos. In the early Universe they can alter the helium
abundance which is tightly constrained by observations. Here I calculate to
what extent torsion of the string theory type leads to a disagreement with the
Big Bang nucleosynthesis predictions.Comment: accepted by General Relativity and Gravitatio
Multiple scattering of matter waves: an analytic model of the refractive index for atomic and molecular gases
We present an analytic model of the refractive index for matter waves
propagating through atomic or molecular gases. The model, which combines a WKB
treatment of the long range attraction with the Fraunhofer model treatment of
the short range repulsion, furnishes a refractive index in compelling agreement
with recent experiments of Jacquey et al. [Phys. Rev. Lett. 98, 240405 (2007)]
on Li atom matter waves passing through dilute noble gases. We show that the
diffractive contribution, which arises from scattering by a two dimensional
"hard core" of the potential, is essential for obtaining a correct imaginary
part of the refractive index.Comment: 5 pages, 1 figure, 2 table
Association of One-Step Nucleic Acid Amplification Detected Micrometastases with Tumour Biology and Adjuvant Chemotherapy.
One-step nucleic acid amplification (OSNA) is an intraoperative technique with a high sensitivity and specificity for sentinel node assessment. The aim of this study was to assess the impact of OSNA on micrometastases detection rates and use of adjuvant chemotherapy. A retrospective review of patients with sentinel node micrometastases over a five-year period was carried out and a comparison of micrometastases detection using OSNA and H&E techniques was made. Out of 1285 patients who underwent sentinel node (SLN) biopsy, 76 patients had micrometastases. Using H&E staining, 36 patients were detected with SLN micrometastases (9/year) in contrast to 40 patients in the OSNA year (40/year) (p< 0.0001), demonstrating a fourfold increase with the use of OSNA. In the OSNA group, there was also a proportional increase in Grade III, triple-negative, ER-negative, and HER-2-positive tumours being diagnosed with micrometastases. Also on interactive PREDICT tool, the number of patients with a predicted 10-year survival benefit of more than 3% with adjuvant chemotherapy increased from 52 to 70 percent. OSNA has resulted in an increased detection rate of micrometastases especially in patients with aggressive tumour biology. This increased the number of patients who had a predicted survival benefit from adjuvant chemotherapy
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Evidence of neutral transcriptome evolution in plants
The transcriptome of an organism is its set of gene transcripts (mRNAs) at a defined spatial and temporal locus. Because gene expression is affected markedly by
environmental and developmental perturbations, it is widely assumed that transcriptome divergence among taxa represents adaptive phenotypic selection. This assumption has been challenged by neutral theories which propose that stochastic
processes drive transcriptome evolution. To test for evidence of neutral transcriptome evolution in plants, we quantified 18 494 gene transcripts in nonsenescent leaves of 14 taxa of Brassicaceae using robust cross-species transcriptomics which includes a two-step physical and in silicobased normalization procedure based on DNA similarity among taxa. Transcriptome divergence correlates positively with evolutionary distance between taxa and with variation in gene expression among samples. Results are similar for pseudogenes and chloroplast genes evolving at different rates. Remarkably, variation in transcript abundance among root-cell samples correlates positively with
transcriptome divergence among root tissues and among taxa.
Because neutral processes affect transcriptome evolution in plants, many differences in gene expression among or within taxa may be nonfunctional, reflecting ancestral
plasticity and founder effects. Appropriate null models are required when comparing transcriptomes in space and time
Lifetime measurements of Triaxial Strongly Deformed bands in Tm
With the Doppler Shift Attenuation Method, quadrupole transition moments,
, were determined for the two recently proposed Triaxial Strongly Deformed
(TSD) bands in Tm. The measured moments indicate that the
deformation of these bands is larger than that of the yrast, signature
partners. However, the measured values are smaller than those predicted by
theory. This observation appears to be valid for TSD bands in several nuclei of
the regionComment: 8 pages, 5 figures. Submitted to Physical Review
Transport analysis in an uncertain world
This short article reflects upon the task of informing policymaking and investment decisions in times of deep uncertainty, in the face of problems that are more 'wicked' than 'tame' and in the context of ever present biases
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