1,041 research outputs found
Optical coherence tomography in neuromyelitis optica spectrum disorders: potential advantages for individualized monitoring of progression and therapy
Neuromyelitis optica spectrum disorders (NMOSD) are mostly relapsing inflammatory disorders of the central nervous system (CNS). Optic neuritis (ON) is the first NMOSD-related clinical event in 55% of the patients, which causes damage to the optic nerve and leads to visual impairment. Retinal optical coherence tomography (OCT) has emerged as a promising method for diagnosis of NMOSD and potential individual monitoring of disease course and severity. OCT not only detects damage to the afferent visual system caused by ON but potentially also NMOSD-specific intraretinal pathology, i.e. astrocytopathy. This article summarizes retinal involvement in NMOSD and reviews OCT methods that could be used now and in the future, for differential diagnosis, for monitoring of disease course, and in clinical trials
Mobile intraoperative CT-assisted frameless stereotactic biopsies achieved single-millimeter trajectory accuracy for deep-seated brain lesions in a sample of 7 patients
BACKGROUND
Brain biopsies are crucial diagnostic interventions, providing valuable information for treatment and prognosis, but largely depend on a high accuracy and precision. We hypothesized that through the combination of neuronavigation-based frameless stereotaxy and MRI-guided trajectory planning with intraoperative CT examination using a mobile unit, one can achieve a seamlessly integrated approach yielding optimal target accuracy.
METHODS
We analyzed a total of 7 stereotactic biopsy trajectories for a variety of deep-seated locations and different patient positions. After rigid head fixation, an intraoperative pre-procedural scan using a mobile CT unit was performed for automatic image fusion with the planning MRI images and a peri-procedural scan with the biopsy cannula in situ for verification of the definite target position. We then evaluated the radial trajectory error.
RESULTS
Intraoperative scanning, surgery, computerized merging of MRI and CT images as well as trajectory planning were feasible without difficulties and safe in all cases. We achieved a radial trajectory deviation of 0.97 ± 0.39 mm at a trajectory length of 60 ± 12.3 mm (mean ± standard deviation). Repositioning of the biopsy cannula due to inaccurate targeting was not required.
CONCLUSION
Intraoperative verification using a mobile CT unit in combination with frameless neuronavigation-guided stereotaxy and pre-operative MRI-based trajectory planning was feasible, safe and highly accurate. The setting enabled single-millimeter accuracy for deep-seated brain lesions and direct detection of intraoperative complications, did not depend on a dedicated operating room and was seamlessly integrated into common stereotactic procedures
Deep brain electrical neurofeedback allows Parkinson patients to control pathological oscillations and quicken movements
Parkinsonian motor symptoms are linked to pathologically increased beta-oscillations in the basal ganglia. While pharmacological treatment and deep brain stimulation (DBS) reduce these pathological oscillations concomitantly with improving motor performance, we set out to explore neurofeedback as an endogenous modulatory method. We implemented real-time processing of pathological subthalamic beta oscillations through implanted DBS electrodes to provide deep brain electrical neurofeedback. Patients volitionally controlled ongoing beta-oscillatory activity by visual neurofeedback within minutes of training. During a single one-hour training session, the reduction of beta-oscillatory activity became gradually stronger and we observed improved motor performance. Lastly, endogenous control over deep brain activity was possible even after removing visual neurofeedback, suggesting that neurofeedback-acquired strategies were retained in the short-term. Moreover, we observed motor improvement when the learnt mental strategies were applied 2 days later without neurofeedback. Further training of deep brain neurofeedback might provide therapeutic benefits for Parkinson patients by improving symptom control using strategies optimized through neurofeedback
The Computational Complexity of Knot and Link Problems
We consider the problem of deciding whether a polygonal knot in 3-dimensional
Euclidean space is unknotted, capable of being continuously deformed without
self-intersection so that it lies in a plane. We show that this problem, {\sc
unknotting problem} is in {\bf NP}. We also consider the problem, {\sc
unknotting problem} of determining whether two or more such polygons can be
split, or continuously deformed without self-intersection so that they occupy
both sides of a plane without intersecting it. We show that it also is in NP.
Finally, we show that the problem of determining the genus of a polygonal knot
(a generalization of the problem of determining whether it is unknotted) is in
{\bf PSPACE}. We also give exponential worst-case running time bounds for
deterministic algorithms to solve each of these problems. These algorithms are
based on the use of normal surfaces and decision procedures due to W. Haken,
with recent extensions by W. Jaco and J. L. Tollefson.Comment: 32 pages, 1 figur
Predicting Climate-Driven Coastlines With a Simple and Efficient Multiscale Model
Ocean-basin-scale climate variability produces shifts in wave climates and water levels affecting the coastlines of the basin. Here we present a hybrid shoreline change?foredune erosion model (A COupled CrOss-shOre, loNg-shorE, and foreDune evolution model, COCOONED) intended to inform coastal planning and adaptation. COCOONED accounts for coupled longshore and cross-shore processes at different timescales, including sequencing and clustering of storm events, seasonal, interannual, and decadal oscillations by incorporating the effects of integrated varying wave action and water levels for coastal hazard assessment. COCOONED is able to adapt shoreline change rates in response to interactions between longshore transport, cross-shore transport, water level variations, and foredune erosion. COCOONED allows for the spatial and temporal extension of survey data using global data sets of waves and water levels for assessing the behavior of the shoreline at multiple time and spatial scales. As a case study, we train the model in the period 2004?2014 (11 years) with seasonal topographic beach profile surveys from the North Beach Sub-cell (NBSC) of the Columbia River Littoral Cell (Washington, USA).We explore the shoreline response and foredune erosion along 40 km of beach at several timescales during the period 1979?2014 (35 years), revealing an accretional trend producing reorientation of the beach, cross-shore accretional, and erosional periods through time (breathing) and alternating beach rotations that are correlated with climate indices.J. A. A.
Antolínez and F. J. Méndez
acknowledge the support of the
Spanish “Ministerio de Economia y
Competitividad” under Grant
BIA2014-59643-R
Meson loop effects in the NJL model at zero and non-zero temperature
We compare two different possibilities to include meson-loop corrections in
the Nambu-Jona-Lasinio model: a strict 1/N_c-expansion in next-to-leading order
and a non-perturbative scheme corresponding to a one-meson-loop approximation
to the effective action. Both schemes are consistent with chiral symmetry, in
particular with the Goldstone theorem and the Gell-Mann-Oakes-Renner relation.
The numerical part at zero temperature focuses on the pion and the rho-meson
sector. For the latter the meson-loop-corrections are crucial in order to
include the dominant rho -> pipi-decay channel, while the standard Hartree +
RPA approximation only contains unphysical qqbar-decay channels. We find that
m_\pi, f_\pi, and quantities related to the rho-meson self-energy can
be described reasonably with one parameter set in the 1/N_c-expansion scheme,
whereas we did not succeed to obtain such a fit in the non-perturbative scheme.
We also investigate the temperature dependence of the quark condensate. Here we
find consistency with chiral perturbation theory to lowest order. Similarities
and differences of both schemes are discussed.Comment: 51 pages, 18 figures, to be published in Physics of Atomic Nuclei,
the volume dedicated to the 90th birthday of A.B. Migdal, error in Eq. 4.22
correcte
Dispersive representation and shape of the Kl3 form factors: robustness
An accurate low-energy dispersive parametrization of the scalar Kpi form
factor was constructed some time ago in terms of a single parameter guided by
the Callan-Treiman low-energy theorem. A similar twice subtracted dispersive
parametrization for the vector Kpi form factor will be investigated here. The
robustness of the parametrization of these two form factors will be studied in
great detail. In particular the cut-off dependence, the isospin breaking
effects and the possible, though not highly probable, presence of zeros in the
form factors will be discussed. Interesting constraints in the latter case will
be obtained from the soft-kaon analog of the Callan-Treiman theorem and a
comparison with the recent tau --> K pi nu_tau data.Comment: 24 pages, 11 figure
Neutron stars and the transition to color-superconducting quark matter
We explore the relevance of color superconductivity inside a possible quark
matter core for the bulk properties of neutron stars. For the quark phase we
use an Nambu--Jona-Lasinio (NJL) type model, extended to include diquark
condensates. For the hadronic phase, a microscopic many-body model is adopted,
with and without strangeness content. In our calculations, a sharp boundary is
assumed between the hadronic and the quark phases. For NJL model parameters
fitted to vacuum properties we find that no star with a pure quark core does
exist. Nevertheless the presence of color superconducting phases can lower the
neutron star maximum mass substantially. In some cases, the transition to quark
matter occurs only if color superconductivity is present. Once the quark phase
is introduced, the value of the maximum mass stays in any case below the value
of two solar masses.Comment: 11 pages, 3 figures, v2: minor corrections in the text, layout of the
figures improved, references added, v3: transition densities from hadronic to
quark matter added, version accepted for publication in PL
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