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Search Results: 1 - 10 of 14106 matches for " Jan Mehnert "
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Decoding Vigilance with NIRS
Carsten Bogler, Jan Mehnert, Jens Steinbrink, John-Dylan Haynes
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0101729
Abstract: Sustained, long-term cognitive workload is associated with variations and decrements in performance. Such fluctuations in vigilance can be a risk factor especially during dangerous attention demanding activities. Functional MRI studies have shown that attentional performance is correlated with BOLD-signals, especially in parietal and prefrontal cortical regions. An interesting question is whether these BOLD-signals could be measured in real-world scenarios, say to warn in a dangerous workplace whenever a subjects' vigilance is low. Because fMRI lacks the mobility needed for such applications, we tested whether the monitoring of vigilance might be possible using Near-Infrared Spectroscopy (NIRS). NIRS is a highly mobile technique that measures hemodynamics in the surface of the brain. We demonstrate that non-invasive NIRS signals correlate with vigilance. These signals carry enough information to decode subjects' reaction times at a single trial level.
Climate Change Futures and the Imagination of the Global in Maeva! by Dirk C. Fleck
Antonia Mehnert
Ecozon@ : European Journal of Literature, Culture and Environment , 2012,
Abstract: This article is aimed at making a contribution to the only recently emerging literary criticism of climate change fiction. Facing a global environmental disaster such as climate change requires a departure from an overemphasis on place in ecocriticism. Incorporating ideas from the concept of eco-cosmopolitanism can therefore be helpful for the analysis of literary works dealing with global warming, opening up new planetary perspectives. However, while many climate change novels fall short of engaging with the global, D. Fleck’s Maeva! serves as a counter-example from German science fiction. This article therefore explores the ways in which Fleck’s novel embraces an “eco-cosmopolitan manifesto” as a political vision of dealing with the climatically changed world of tomorrow while showing that this thereby newly created “space” is contested and fragile as interests between the local and the global have to be constantly re-negotiated. Finally, this article also discusses Fleck’s innovative textual approach, which can be read as an attempt at imagineering—creating a manual for critical intervention derived from creative ideas.
Editorial: Probleme m nnlicher Diabetiker
Mehnert H
Blickpunkt der Mann , 2004,
Towards Whole-Body Fluorescence Imaging in Humans
Sophie K. Piper, Christina Habermehl, Christoph H. Schmitz, Wolfgang M. Kuebler, Hellmuth Obrig, Jens Steinbrink, Jan Mehnert
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0083749
Abstract: Dynamic near-infrared fluorescence (DNIF) whole-body imaging of small animals has become a popular tool in experimental biomedical research. In humans, however, the field of view has been limited to body parts, such as rheumatoid hands, diabetic feet or sentinel lymph nodes. Here we present a new whole-body DNIF-system suitable for adult subjects. We explored whether this system (i) allows dynamic whole-body fluorescence imaging and (ii) can detect modulations in skin perfusion. The non-specific fluorescent probe indocyanine green (ICG) was injected intravenously into two subjects, and fluorescence images were obtained at 5 Hz. The in- and out-flow kinetics of ICG have been shown to correlate with tissue perfusion. To validate the system, skin perfusion was modulated by warming and cooling distinct areas on the chest and the abdomen. Movies of fluorescence images show a bolus passage first in the face, then in the chest, abdomen and finally in the periphery (~10, 15, 20 and 30 seconds, respectively). When skin perfusion is augmented by warming, bolus arrives about 5 seconds earlier than when the skin is cooled and perfusion decreased. Calculating bolus arrival times and spatial fitting of basis time courses extracted from different regions of interest allowed a mapping of local differences in subcutaneous skin perfusion. This experiment is the first to demonstrate the feasibility of whole-body dynamic fluorescence imaging in humans. Since the whole-body approach demonstrates sensitivity to circumscribed alterations in skinperfusion, it may be used to target autonomous changes in polyneuropathy and to screen for peripheral vascular diseases.
Predicting BCI Subject Performance Using Probabilistic Spatio-Temporal Filters
Heung-Il Suk, Siamac Fazli, Jan Mehnert, Klaus-Robert Müller, Seong-Whan Lee
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0087056
Abstract: Recently, spatio-temporal filtering to enhance decoding for Brain-Computer-Interfacing (BCI) has become increasingly popular. In this work, we discuss a novel, fully Bayesian–and thereby probabilistic–framework, called Bayesian Spatio-Spectral Filter Optimization (BSSFO) and apply it to a large data set of 80 non-invasive EEG-based BCI experiments. Across the full frequency range, the BSSFO framework allows to analyze which spatio-spectral parameters are common and which ones differ across the subject population. As expected, large variability of brain rhythms is observed between subjects. We have clustered subjects according to similarities in their corresponding spectral characteristics from the BSSFO model, which is found to reflect their BCI performances well. In BCI, a considerable percentage of subjects is unable to use a BCI for communication, due to their missing ability to modulate their brain rhythms–a phenomenon sometimes denoted as BCI-illiteracy or inability. Predicting individual subjects’ performance preceding the actual, time-consuming BCI-experiment enhances the usage of BCIs, e.g., by detecting users with BCI inability. This work additionally contributes by using the novel BSSFO method to predict the BCI-performance using only 2 minutes and 3 channels of resting-state EEG data recorded before the actual BCI-experiment. Specifically, by grouping the individual frequency characteristics we have nicely classified them into the subject ‘prototypes’ (like μ - or β -rhythm type subjects) or users without ability to communicate with a BCI, and then by further building a linear regression model based on the grouping we could predict subjects' performance with the maximum correlation coefficient of 0.581 with the performance later seen in the actual BCI session.
High-resolution optical functional mapping of the human somatosensory cortex
Stefan P. Koch,Christina Habermehl,Jan Mehnert,Christoph H. Schmitz,Susanne Holtze,Arno Villringer,Jens Steinbrink,Hellmuth Obrig
Frontiers in Neuroenergetics , 2010, DOI: 10.3389/fnene.2010.00012
Abstract: Non-invasive optical imaging of brain function has been promoted in a number of fields in which functional magnetic resonance imaging (fMRI) is limited due to constraints induced by the scanning environment. Beyond physiological and psychological research, bedside monitoring and neurorehabilitation may be relevant clinical applications that are yet little explored. A major obstacle to advocate the tool in clinical research is insufficient spatial resolution. Based on a multi-distance high-density optical imaging setup, we here demonstrate a dramatic increase in sensitivity of the method. We show that optical imaging allows for the differentiation between activations of single finger representations in the primary somatosensory cortex (SI). Methodologically our findings confirm results in a pioneering study by Zeff et al. (2007) and extend them to the homuncular organization of SI. After performing a motor task, eight subjects underwent vibrotactile stimulation of the little finger and the thumb. We used a high-density diffuse-optical sensing array in conjunction with optical tomographic reconstruction. Optical imaging disclosed three discrete activation foci one for motor and two discrete foci for vibrotactile stimulation of the first and fifth finger, respectively. The results were co-registered to the individual anatomical brain anatomy (MRI) which confirmed the localization in the expected cortical gyri in four subjects. This advance in spatial resolution opens new perspectives to apply optical imaging in the research on plasticity notably in patients undergoing neurorehabilitation.
A Comparative Study of Automated Segmentation Methods for Use in a Microwave Tomography System for Imaging Intracerebral Hemorrhage in Stroke Patients  [PDF]
Qaiser Mahmood, Shaochuan Li, Andreas Fhager, Stefan Candefjord, Artur Chodorowski, Andrew Mehnert, Mikael Persson
Journal of Electromagnetic Analysis and Applications (JEMAA) , 2015, DOI: 10.4236/jemaa.2015.75017
Abstract: Microwave technology offers the possibility for pre-hospital stroke detection as we have previously demonstrated using non-imaging diagnostics. The focus in this paper is on image-based diagnostics wherein the technical and computational complexities of image reconstruction are a challenge for clinical realization. Herein we investigate whether information about a patient’s brain anatomy obtained prior to a stroke event can be used to facilitate image-based stroke diagnostics. A priori information can be obtained by segmenting the patient’s head tissues from magnetic resonance images. Expert manual segmentation is presently the gold standard, but it is laborious and subjective. A fully automatic method is thus desirable. This paper presents an evaluation of several such methods using both synthetic magnetic resonance imaging (MRI) data and real data from four healthy subjects. The segmentation was performed on the full 3D MRI data, whereas the electromagnetic evaluation was performed using a 2D slice. The methods were evaluated in terms of: i) tissue classification accuracy over all tissues with respect to ground truth, ii) the accuracy of the simulated electromagnetic wave propagation through the head, and iii) the accuracy of the image reconstruction of the hemorrhage. The segmentation accuracy was measured in terms of the degree of overlap (Dice score) with the ground truth. The electromagnetic simulation accuracy was measured in terms of signal deviation relative to the simulation based on the ground truth. Finally, the image reconstruction accuracy was measured in terms of the Dice score, relative error of dielectric properties, and visual comparison between the true and reconstructed intracerebral hemorrhage. The results show that accurate segmentation of tissues (Dice score = 0.97) from the MRI data can lead to accurate image reconstruction (relative error = 0.24) for the intracerebral hemorrhage in the subject’s brain. They also suggest that accurate automated segmentation can be used as a surrogate for manual segmentation and can facilitate the rapid diagnosis of intracerebral hemorrhage in stroke patients using a microwave imaging system.
Efficacy of a Multimodal Cognitive Rehabilitation Including Psychomotor and Endurance Training in Parkinson's Disease
I. Reuter,S. Mehnert,G. Sammer,M. Oechsner,M. Engelhardt
Journal of Aging Research , 2012, DOI: 10.1155/2012/235765
Abstract: Mild cognitive impairment, especially executive dysfunction might occur early in the course of Parkinson's disease. Cognitive training is thought to improve cognitive performance. However, transfer of improvements achieved in paper and pencil tests into daily life has been difficult. The aim of the current study was to investigate whether a multimodal cognitive rehabilitation programme including physical exercises might be more successful than cognitive training programmes without motor training. 240?PD-patients were included in the study and randomly allocated to three treatment arms, group A cognitive training, group B cognitive training and transfer training and group C cognitive training, transfer training and psychomotor and endurance training. The primary outcome measure was the ADAS-Cog. The secondary outcome measure was the SCOPA-Cog. Training was conducted for 4 weeks on a rehabilitation unit, followed by 6 months training at home. Caregivers received an education programme. The combination of cognitive training using paper and pencil and the computer, transfer training and physical training seems to have the greatest effect on cognitive function. Thus, patients of group C showed the greatest improvement on the ADAS-Cog and SCOPA-COG and were more likely to continue with the training programme after the study. 1. Introduction Idiopathic Parkinson’s disease (PD) is a neurodegenerative disorder characterized by loss of dopaminergic neurons and basal ganglia dysfunction. The prevalence of PD increases with age and is estimated in 100–200/100000 people [1, 2] worldwide. The clinical hallmarks of PD are akinesia, rigidity, and tremor [3, 4]. However, a spectrum of nonmotor symptoms occurs in Parkinson’s disease. One of the most disabling symptoms is dementia, which is common among patients with PD with an average prevalence of 40% in cross-sectional studies and a cumulative prevalence approaching 80% [5, 6]. PD dementia is the third most common reason for dementia and is associated with rapid functional and motor decline, shortened survival [7], greater sensitivity to medication, higher risk of developing psychosis, reduced quality of life for both patients [8] and caregivers [9], increased caregivers’ stress, and frequent transfer to nursing homes [10]. Clinical characteristics of PD dementia are cognitive slowing, executive deficits, visuospatial deficits, and memory impairments [11]. Pathological findings include Lewy bodies outside the substantia nigra, neurofibrillary tangles, and amyloid plaques [12]. Neurochemically, cholinergic deficits are
Allogeneic blood transfusion and prognosis following total hip replacement: a population-based follow up study
Alma B Pedersen, Frank Mehnert, Soren Overgaard, Soren P Johnsen
BMC Musculoskeletal Disorders , 2009, DOI: 10.1186/1471-2474-10-167
Abstract: A population-based follow-up study was performed using data from medical databases in Denmark. We identified 28,087 primary THR procedures performed from 1999 to 2007, from which we computed a propensity score for red blood cell transfusion based on detailed data on patient-, procedure-, and hospital-related characteristics. We were able to match 2,254 transfused with 2,254 non-transfused THR patients using the propensity score.Of the 28,087 THR patients, 9,063 (32.3%) received at least one red blood cell transfusion within 8 days of surgery. Transfused patients had higher 90-day mortality compared with matched non-transfused patients: the adjusted OR was 2.2 (95% confidence interval (CI): 1.2-3.8). Blood transfusion was also associated with increased odds of pneumonia (OR 2.1; CI: 1.2-3.8), whereas the associations with cardiovascular or cerebrovascular events (OR 1.4; CI: 0.9-2.2) and venous thromboembolism (OR 1.2; CI: 0.7-2.1) did not reach statistical significance. The adjusted OR of reoperation due to infection was 0.6 (CI: 0.1-2.9).Red blood cell transfusion was associated with an adverse prognosis following primary THR, in particular with increased odds of death and pneumonia. Although the odds estimates may partly reflect unmeasured bias due to blood loss, they indicate the need for careful assessment of the risk versus benefit of transfusion even in relation to routine THR procedures.Primary total hip replacement (THR) is a common surgical procedure in developed countries, and incidence rates appear to be increasing [1-3]. Although THR surgery is an elective procedure (i.e. there is usually time to haemodynamically stabilize the patient preoperatively), it is associated with blood loss resulting in transfusion rates between 30-80% [4,5]. Considerable evidence points to an increase in the risk of serious complications and death in critically ill patients who are transfused, especially in patients who are undergoing cardiac surgery [6-9]. However, data is li
Treatment of Recurrent Metastatic Head and Neck Cancer: Focus on Cetuximab
Akshar N. Patel, Janice M. Mehnert and Sung Kim
Clinical Medicine Insights: Ear, Nose and Throat , 2012, DOI: 10.4137/CMENT.S5129
Abstract: EGFR belongs to the ErbB family of receptor tyrosine kinases and is associated with worse prognosis in head and neck squamous cell carcinoma (HNSCC). Cetuximab is a monoclonal antibody to the extracellular domain of EGFR and inhibits its downstream actions via multiple mechanisms. Besides its proven efficacy in locally advanced and incurable HNSCC, cetuximab has the distinct advantage of having a relatively tolerable side effect profile and not potentiating radiation toxicity. Though therapies for advanced HNSCC are evolving, locoregional recurrence and/or distant metastases occur in a large percentage of patients. Though some patients can be salvaged with surgery or radiation therapy, the majority are incurable, and are treated palliatively with systemic therapy. In the setting of first line therapy for recurrent/metastatic HNSCC, the EXTREME trial provided level 1 evidence that cetuximab improves overall survival when combined with cisplatinum and 5 FU. Following progression on first line chemotherapy, several phase II trials suggest that cetuximab monotherapy is a reasonable choice in this setting. Future studies should concentrate on clinical and molecular markers that may allow more personalized approaches to treating HNSCC, and combining EGFR inhibitors with other agents in a synergistic approach.
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