1,379 research outputs found
Myokardiale MRT-Perfusionsbildgebung bei 3 Tesla im Vergleich zu 1,5 Tesla
Ziel der vorliegenden Arbeit war die Evaluation einer neuen rĂ€umlich hochauflösenden Kont-rastmittel-verstĂ€rkten MRT-Sequenz zur Darstellung der myokardialen Perfusion bei 3 Tesla im Vergleich zu einer Standard-Perfusionsuntersuchung bei 1,5 Tesla in einem Probandenkollektiv (n=26). Beide Sequenzen wurden in Hinblick auf BildqualitĂ€t, Bildkontrast und die Anzahl der âdark rimâ Artefakte miteinander verglichen. Bei beiden FeldstĂ€rken wurde zur Signalakquisition eine T1-gewichtete TFE-Sequenz mit Satura-tion-Recovery-Vorpuls und segmentierter k-Raum-Konstruktion in Verbindung mit paralleler Bildgebung (SENSE) eingesetzt. Alle 26 Probandinnen und Probanden nahmen an den Untersu-chungen bei 3 Tesla (Pixeldimensionen 3,78 mm2) und 1,5 Tesla (Pixeldimensionen 9,86 mm2) teil. AnschlieĂend wurden aus den generierten Daten die CER und BildqualitĂ€t (1, nicht diagnos-tisch bis 4, exzellente BildqualitĂ€t) bestimmt. Zudem fĂŒhrten wir eine semiquantitative Analyse der Anzahl von âdark rimâ Artefakten durch. In den hochauflösenden MRT-Sequenzen bei 3 Tesla ergaben sich im Vergleich zu 1,5 T eine leicht verbesserte CER (1,31 ± 0,32 bei 3 T; 1,14 ± 0,34 bei 1,5 T; p Die rĂ€umlich hochauflösenden âfirst-passâ Perfusionssequenz ist â bei Perfusionsuntersuchungen in Ruhelage â einer Standard-Perfusionssequenz bei 1,5 Tesla in Bezug auf die BildqualitĂ€t und die Anzahl der âdark rimâ Artefakte ĂŒberlegen
Deuterium Chemodynamics of Massive Pre-Stellar Cores
High levels of deuterium fractionation of (i.e., ) are often observed in pre-stellar cores (PSCs)
and detection of is a promising method to identify elusive massive
PSCs. However, the physical and chemical conditions required to reach such high
levels of deuteration are still uncertain, as is the diagnostic utility of and observations of PSCs. We perform 3D
magnetohydrodynamics simulations of a massive, turbulent, magnetised PSC,
coupled with a sophisticated deuteration astrochemical network. Although the
core has some magnetic/turbulent support, it collapses under gravity in about
one freefall time, which marks the end of the simulations. Our fiducial model
achieves relatively low during this time. We
then investigate effects of initial ortho-para ratio of (), temperature, cosmic ray (CR) ionization rate, CO and N-species
depletion factors and prior PSC chemical evolution. We find that high CR
ionization rates and high depletion factors allow the simulated and absolute abundances to match observational values within
one freefall time. For , while a lower initial value helps the
growth of , the spatial structure of deuteration is too
widespread compared to observed systems. For an example model with elevated CR
ionization rates and significant heavy element depletion, we then study the
kinematic and dynamic properties of the core as traced by its
emission. The core, undergoing quite rapid collapse, exhibits disturbed
kinematics in its average velocity map. Still, because of magnetic support, the
core often appears kinematically sub-virial based on its velocity
dispersion.Comment: 25 pages, 20 figures, 2 tables, accepted for publication in MNRAS,
comments welcom
Stroke with unknown time of symptom onset: baseline clinical and magnetic resonance imaging data of the first thousand patients in WAKE-UP (efficacy and safety of mri-based thrombolysis in wake-up stroke: a randomized, doubleblind, placebo-controlled trial)
Background and PurposeâWe describe clinical and magnetic resonance imaging (MRI) characteristics of stroke patients with unknown time of symptom onset potentially eligible for thrombolysis from a large prospective cohort.
MethodsâWe analyzed baseline data from WAKE-UP (Efficacy and Safety of MRI-Based Thrombolysis in Wake-Up Stroke: A Randomized, Doubleblind, Placebo-Controlled Trial), an investigator-initiated, randomized, placebo-controlled trial of MRI-based thrombolysis in stroke patients with unknown time of symptom onset. MRI judgment included assessment of the mismatch between visibility of the acute ischemic lesion on diffusion-weighted imaging and fluid-attenuated inversion recovery.
ResultsâOf 1005 patients included, diffusion-weighted imaging and fluid-attenuated inversion recovery mismatch was present in 479 patients (48.0%). Patients with daytime-unwitnessed stroke (n=138, 13.7%) had a shorter delay between symptom recognition and hospital arrival (1.5 versus 1.8 hours; P=0.002), a higher National Institutes of Stroke Scale score on admission (8 versus 6; P<0.001), and more often aphasia (72.5% versus 34.0%; P<0.001) when compared with stroke patients waking up from nighttime sleep. Frequency of diffusion-weighted imaging and fluid-attenuated inversion recovery mismatch was comparable between both groups (43.7% versus 48.7%; P=0.30).
ConclusionsâAlmost half of the patients with unknown time of symptom onset stroke otherwise eligible for thrombolysis had MRI findings making them likely to be within a time window for safe and effective thrombolysis. Patients with daytime onset unwitnessed stroke differ from wake-up stroke patients with regards to clinical characteristics but are comparable in terms of MRI characteristics of lesion age.
Clinical Trial RegistrationâURL: http://www.clinicaltrials.gov. Unique identifier: NCT01525290. URL: https://www.clinicaltrialsregister.eu. Unique identifier: 2011-005906-32
Clinical characteristics of unknown symptom onset stroke patients with and without diffusion-weighted imaging and fluid-attenuated inversion recovery mismatch
Background:
Diffusion-weighted imaging (DWI) and fluid-attenuated inversion recovery (FLAIR) mismatch was suggested to identify stroke patients with unknown time of symptom onset likely to be within the time window for thrombolysis.
Aims:
We aimed to study clinical characteristics associated with DWI-FLAIR mismatch in patients with unknown onset stroke.
Methods:
We analyzed baseline MRI and clinical data from patients with acute ischemic stroke proven by DWI from WAKE-UP, an investigator-initiated, randomized, placebo-controlled trial of MRI-based thrombolysis in stroke patients with unknown time of symptom onset. Clinical characteristics were compared between patients with and without DWI-FLAIR mismatch.
Results:
Of 699 patients included, 418 (59.8%) presented with DWI-FLAIR mismatch. A shorter delay between last seen well and symptom recognition (pâ=â0.0063), a shorter delay between symptom recognition and arrival at hospital (pâ=â0.0025), and history of atrial fibrillation (pâ=â0.19) were predictors of DWI-FLAIR mismatch in multivariate analysis. All other characteristics were comparable between groups.
Conclusions:
There are only minor differences in measured clinical characteristics between unknown symptom onset stroke patients with and without DWI-FLAIR mismatch. DWI-FLAIR mismatch as an indicator of stroke onset within 4.5âh shows no relevant association with commonly collected clinical characteristics of stroke patients
Effect of informed consent on patient characteristics in a stroke thrombolysis trial
Objective: To determine whether the manner of consent, i.e., informed consent by patients themselves or informed consent by proxy, affects clinical characteristics of samples of acute stroke patients enrolled in clinical trials.
Methods: We analyzed the manner of obtaining informed consent in the first 1,005 patients from WAKE-UP, an investigator-initiated, randomized, placebo-controlled trial of MRI-based thrombolysis in stroke patients with unknown time of symptom onset running in 6 European countries. Patients providing informed consent by themselves were compared with patients enrolled by proxy consent. Baseline clinical measures were compared between groups.
Results: In 359 (35.7%) patients, informed consent was by proxy. Patients with proxy consent were older (median 71 vs 66 years, p < 0.0001) and had a higher frequency of arterial hypertension (58.2% vs 43.4%, p < 0.0001). They showed higher scores on the NIH Stroke Scale (median 11 vs 5, p < 0.0001) and more frequently aphasia (73.7% vs 20.0%, p < 0.0001). The rate of proxy consent varied among countries (p < 0.0001), ranging from 77.1% in Spain to 1.2% in Denmark.
Conclusions: Patients recruited by proxy consent were older, had more severe strokes, and had higher prevalence of aphasia than those with capacity to give personal consent. Variations in the manner of consent across countries may influence trial results.
Clinicaltrials.gov and Clinicaltrialsregister.eu identifiers: NCT01525290 (clinicaltrials.gov); 2011-005906-32 (clinicaltrialsregister.eu)
Successive Solar Flares and Coronal Mass Ejections on 2005 September 13 from Noaa Ar 10808
We present a multiwavelength study of the 2005 September 13 eruption from
NOAA 10808 that produced total four flares and two fast coronal mass ejections
(CMEs) within 1.5 hours. Our primary attention is paid to the fact that these
eruptions occurred in close succession in time, and that all of them were
located along an S-shaped magnetic polarity inversion line (PIL) of the active
region. In our analysis, (1) the disturbance created by the first flare
propagated southward along the PIL to cause a major filament eruption that led
to the first CME and the associated second flare underneath. (2) The first CME
partially removed the overlying magnetic fields over the northern Delta spot to
allow the third flare and the second CME. (3) The ribbon separation during the
fourth flare would indicate reclosing of the overlying field lines opened by
the second CME. It is thus concluded that this series of flares and CMEs are
interrelated to each other via magnetic reconnections between the expanding
magnetic structure and the nearby magnetic fields. These results complement
previous works made on this event with the suggested causal relationship among
the successive eruptions.Comment: 11 pages, 8 figures, 2 tables, accepted to The Astrophysical Journa
Multiple Instance Ensembling For Paranasal Anomaly Classification In The Maxillary Sinus
Paranasal anomalies are commonly discovered during routine radiological
screenings and can present with a wide range of morphological features. This
diversity can make it difficult for convolutional neural networks (CNNs) to
accurately classify these anomalies, especially when working with limited
datasets. Additionally, current approaches to paranasal anomaly classification
are constrained to identifying a single anomaly at a time. These challenges
necessitate the need for further research and development in this area.
In this study, we investigate the feasibility of using a 3D convolutional
neural network (CNN) to classify healthy maxillary sinuses (MS) and MS with
polyps or cysts. The task of accurately identifying the relevant MS volume
within larger head and neck Magnetic Resonance Imaging (MRI) scans can be
difficult, but we develop a straightforward strategy to tackle this challenge.
Our end-to-end solution includes the use of a novel sampling technique that not
only effectively localizes the relevant MS volume, but also increases the size
of the training dataset and improves classification results. Additionally, we
employ a multiple instance ensemble prediction method to further boost
classification performance. Finally, we identify the optimal size of MS volumes
to achieve the highest possible classification performance on our dataset.
With our multiple instance ensemble prediction strategy and sampling
strategy, our 3D CNNs achieve an F1 of 0.85 whereas without it, they achieve an
F1 of 0.70.
We demonstrate the feasibility of classifying anomalies in the MS. We propose
a data enlarging strategy alongside a novel ensembling strategy that proves to
be beneficial for paranasal anomaly classification in the MS
Unsupervised Anomaly Detection of Paranasal Anomalies in the Maxillary Sinus
Deep learning (DL) algorithms can be used to automate paranasal anomaly
detection from Magnetic Resonance Imaging (MRI). However, previous works relied
on supervised learning techniques to distinguish between normal and abnormal
samples. This method limits the type of anomalies that can be classified as the
anomalies need to be present in the training data. Further, many data points
from normal and anomaly class are needed for the model to achieve satisfactory
classification performance. However, experienced clinicians can segregate
between normal samples (healthy maxillary sinus) and anomalous samples
(anomalous maxillary sinus) after looking at a few normal samples. We mimic the
clinicians ability by learning the distribution of healthy maxillary sinuses
using a 3D convolutional auto-encoder (cAE) and its variant, a 3D variational
autoencoder (VAE) architecture and evaluate cAE and VAE for this task.
Concretely, we pose the paranasal anomaly detection as an unsupervised anomaly
detection problem. Thereby, we are able to reduce the labelling effort of the
clinicians as we only use healthy samples during training. Additionally, we can
classify any type of anomaly that differs from the training distribution. We
train our 3D cAE and VAE to learn a latent representation of healthy maxillary
sinus volumes using L1 reconstruction loss. During inference, we use the
reconstruction error to classify between normal and anomalous maxillary
sinuses. We extract sub-volumes from larger head and neck MRIs and analyse the
effect of different fields of view on the detection performance. Finally, we
report which anomalies are easiest and hardest to classify using our approach.
Our results demonstrate the feasibility of unsupervised detection of paranasal
anomalies from MRIs with an AUPRC of 85% and 80% for cAE and VAE, respectively
Characterization of White Matter Hyperintensities in Large-Scale MRI-Studies
Background: White matter hyperintensities of presumed vascular origin (WMH) are a common finding in elderly people and a growing social malady in the aging western societies. As a manifestation of cerebral small vessel disease, WMH are considered to be a vascular contributor to various sequelae such as cognitive decline, dementia, depression, stroke as well as gait and balance problems. While pathophysiology and therapeutical options remain unclear, large-scale studies have improved the understanding of WMH, particularly by quantitative assessment of WMH. In this review, we aimed to provide an overview of the characteristics, research subjects and segmentation techniques of these studies.Methods: We performed a systematic review according to the PRISMA statement. One thousand one hundred and ninety-six potentially relevant articles were identified via PubMed search. Six further articles classified as relevant were added manually. After applying a catalog of exclusion criteria, remaining articles were read full-text and the following information was extracted into a standardized form: year of publication, sample size, mean age of subjects in the study, the cohort included, and segmentation details like the definition of WMH, the segmentation method, reference to methods papers as well as validation measurements.Results: Our search resulted in the inclusion and full-text review of 137 articles. One hundred and thirty-four of them belonged to 37 prospective cohort studies. Median sample size was 1,030 with no increase over the covered years. Eighty studies investigated in the association of WMH and risk factors. Most of them focussed on arterial hypertension, diabetes mellitus type II and Apo E genotype and inflammatory markers. Sixty-three studies analyzed the association of WMH and secondary conditions like cognitive decline, mood disorder and brain atrophy. Studies applied various methods based on manual (3), semi-automated (57), and automated segmentation techniques (75). Only 18% of the articles referred to an explicit definition of WMH.Discussion: The review yielded a large number of studies engaged in WMH research. A remarkable variety of segmentation techniques was applied, and only a minority referred to a clear definition of WMH. Most addressed topics were risk factors and secondary clinical conditions. In conclusion, WMH research is a vivid field with a need for further standardization regarding definitions and used methods
Remarks on the pion-nucleon sigma-term
The pion-nucleon -term can be stringently constrained by the
combination of analyticity, unitarity, and crossing symmetry with
phenomenological information on the pion-nucleon scattering lengths. Recently,
lattice calculations at the physical point have been reported that find lower
values by about with respect to the phenomenological determination.
We point out that a lattice measurement of the pion-nucleon scattering lengths
could help resolve the situation by testing the values extracted from
spectroscopy measurements in pionic atoms.Comment: 5 pages, 2 figures; version published in PL
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