Authors: Balasso, Andrea | Bauer, Jan S. | Liebig, Thomas | Dorn, Franziska | Zimmer, Claus | Liepsch, Dieter | Prothmann, Sascha
Article Type: Research Article
Abstract: BACKGROUND: The growth and rupture of cerebral aneurysms is intrinsically related to the hemodynamics prevailing in the diseased area. Therefore, a better understanding of intra-aneurysmal hemodynamics is essential for developing effective treatment methods. OBJECTIVE: The intention of this study was to evaluate the intra-aneurysmal flow and flow reduction induced by flow diverters in a true-to-scale elastic aneurysm model, obtained from real patient data. METHODS: Based on the computed tomography angiography (CTA) data of a fusiform aneurysm of a 34 year old patient, an elastic silicon rubber model of the aneurysm was produced. A physiologic pulsatile flow was created with a …circulatory experimental set-up, and a non-Newtonian perfusion fluid was used as a substitute for human blood. Hemodynamics were measured by LDA before and after flow diverter implantation. RESULTS: Implantation of a flow diverter device resulted in a reduction of intra-aneurysmal maximum flow velocities of 97.8% at the inflow zone, 89.1% in the dome and 89.3% at the outflow zone, when compared to the native model. A significant reduction of 94% in the mean intra-aneurysmal velocity was found. CONCLUSIONS: This promising methodology can optimize patient treatment and will correlate with computational simulations to evaluate their reliability. Show more
Keywords: Stent, flow diversion, endovascular, non-Newtonian fluid, laser Doppler anemometry
DOI: 10.3233/BIR-14019
Citation: Biorheology, vol. 51, no. 6, pp. 341-354, 2014
Authors: Neufang, Susanne | Akhrif, Atae | Riedl, Valentin | Förstl, Hans | Kurz, Alexander | Zimmer, Claus | Sorg, Christian | Wohlschläger, Afra M.
Article Type: Research Article
Abstract: In Alzheimer's disease (AD), the loss of cerebral connectivity has been evidenced by numerous studies. There is growing evidence of attention related failures already in prodromal stages of AD; however, connectivity changes within attention networks have been rarely reported. Here we focused on effective connectivity of top-down attention control in patients with prodromal Alzheimer's disease (pAD). We scanned 15 pAD patients and 16 healthy elderly using the Attentional Network Task and determined effective connectivity within a cingulo-fronto-parietal network using Dynamic Causal Modeling. We related connectivity parameters to structural and behavioral parameters (gray matter volume as well as reaction time) to …examine the relation between affected domains. Our analyses revealed that effective connectivity from the right middle frontal gyrus to the left superior parietal cortex as well as from the right to the left superior parietal gyrus was reduced in pAD patients. Furthermore, we found that, effective connectivity varied as a function of GM volume in the patient group: right middle frontal gray matter volume significantly correlated with connectivity from the right parietal cortex to the right middle frontal gyrus as well as from the middle frontal gyrus to the anterior cingulate cortex. In addition, inter-parietal connectivity was correlated to right and left parietal gray matter volume. We conclude that, at very early stages of AD, the reduction of effective connectivity in fronto-parietal circuits is related to regional gray matter volume and contributes to impairments in top-down attentional control. Show more
Keywords: Effective connectivity, prodromal Alzheimer's disease, regional gray matter volume, top down attentional control
DOI: 10.3233/JAD-2011-102154
Citation: Journal of Alzheimer's Disease, vol. 25, no. 2, pp. 309-321, 2011
Authors: Derflinger, Sabine | Sorg, Christian | Gaser, Christian | Myers, Nicholas | Arsic, Milan | Kurz, Alexander | Zimmer, Claus | Wohlschläger, Afra | Mühlau, Mark
Article Type: Research Article
Abstract: In Alzheimer's disease (AD), brain atrophy has been proposed to be left lateralized. Here, we reinvestigated the asymmetry and lateralization (i.e., asymmetry directed toward one hemisphere) of grey-matter (GM) distribution in 35 patients with AD, 24 patients with amnestic mild cognitive impairment (aMCI, a state of increased risk for AD), and 30 age-matched healthy controls (HC). We analyzed GM distribution by applying voxel-based morphometry (VBM) including analyses for asymmetry and lateralization. When comparing MCI with AD patients, VBM revealed GM loss in the entorhinal, temporoparietal, dorsofrontal, and occipital cortices as well as in the precuneus; when comparing HCs with MCI …patients, we found similar differences, which were less pronounced especially within the temporoparietal cortex and precuneus. Analyses of regional asymmetry and regional lateralization as well as global lateralization did not yield significant results. However, lobar asymmetry of the temporal, parietal, and occipital lobes increased from HC to AD. Moreover, in aMCI and AD patients, performance of language-based neuropsychological tests correlated with lateralization of GM loss to the left hemisphere. We conclude that, in principle, brain atrophy in AD is asymmetric rather than lateralized. At the individual level however, asymmetry contributes to cognitive deficits. Show more
Keywords: Alzheimer's disease, asymmetry, CERAD, lateralization, voxel-based morphometry
DOI: 10.3233/JAD-2011-110041
Citation: Journal of Alzheimer's Disease, vol. 25, no. 2, pp. 347-357, 2011
Authors: Hedderich, Dennis M. | Spiro, Judith E. | Goldhardt, Oliver | Kaesmacher, Johannes | Wiestler, Benedikt | Yakushev, Igor | Zimmer, Claus | Boeckh-Behrens, Tobias | Grimmer, Timo
Article Type: Research Article
Abstract: Background: Volumetric quantification of structural MRI has been shown to increase the diagnostic accuracy of patients with mild cognitive impairment (MCI); however, its implementation in clinical routine is usually technically difficult and time-consuming. Objective: The purpose of this study was to investigate whether volumetric information obtained from the free and easy-to-use online tool volBrain can improve correct identification of MCI patients with Alzheimer’s disease (AD) compared to visual reading. Methods: The study cohort consisted of 27 patients with MCI due to AD (AD positive) as determined by biomarker information and 26 cognitively normal controls (CN). Three blinded readers, 2 radiologists …and 1 clinical dementia expert, assessed the patients’ MRI regarding brain atrophy and probability of underlying AD two times, without and with supporting volumetric information from volBrain. To assess diagnostic accuracy of volBrain measures alone, a simple sum score based on basic volumetric measures was developed and tested. Results: Correct patient classification by readers 1, 2, and 3 without a volumetric report was 73.6%, 77.4%, and 83.0%. With a volumetric report, correct classification increased for the radiological readers to 77.4% and 81.1%, respectively and decreased to 77.4% for reader 3. Usage of the volumetric report alone yielded the highest diagnostic accuracy of 84.9%. Diagnostic confidence increased significantly for radiological readers. Conclusion: Volumetric information from volBrain increases the radiologist’s diagnostic performance and confidence in identifying MCI patients with AD. We propose that such tools may be implemented in the routine diagnostic work-up of patients with suspected AD. Show more
Keywords: Alzheimer’s disease, magnetic resonance imaging, mild cognitive impairment, neurodegenerative disease
DOI: 10.3233/JAD-180532
Citation: Journal of Alzheimer's Disease, vol. 65, no. 4, pp. 1459-1467, 2018
Authors: Pasquini, Lorenzo | Scherr, Martin | Tahmasian, Masoud | Myers, Nicholas E. | Ortner, Marion | Kurz, Alexander | Förstl, Hans | Zimmer, Claus | Grimmer, Timo | Akhrif, Atae | Wohlschläger, Afra M. | Riedl, Valentin | Sorg, Christian
Article Type: Research Article
Abstract: In Alzheimer’s disease (AD), disrupted connectivity between medial-parietal cortices and medial-temporal lobes (MTL) is linked with increased MTL local functional connectivity, and parietal atrophy is associated with increased MTL memory activation. We hypothesized that intrinsic activity in MTL subregions is increased and associated with medial-parietal degeneration and impaired memory in AD. To test this hypothesis, resting-state-functional and structural-MRI was assessed in 22 healthy controls, 22 mild cognitive impairment patients, and 21 AD-dementia patients. Intrinsic activity was measured by power-spectrum density of blood-oxygenation-level-dependent signal, medial-parietal degeneration by cortical thinning. In AD-dementia patients, intrinsic activity was increased for several right MTL subregions. …Raised intrinsic activity in dentate gyrus and cornu ammonis 1 was associated with cortical thinning in posterior cingulate cortices, and at-trend with impaired delayed recall. Critically, increased intrinsic activity in the right entorhinal cortex was associated with ipsilateral posterior cingulate degeneration. Our results provide evidence that in AD, intrinsic activity in MTL subregions is increased and associated with medial-parietal atrophy. Results fit a model in which medial-parietal degeneration contributes to MTL dysconnectivity from medial-parietal cortices, potentially underpinning disinhibition-like changes in MTL activity. Show more
Keywords: Alzheimer’s disease, atrophy, functional magnetic resonance imaging, hippocampus, medial-parietal cortex, medial-temporal lobe, neurodegeneration, neuroimaging, physiopathology, resting-state activity
DOI: 10.3233/JAD-150823
Citation: Journal of Alzheimer's Disease, vol. 51, no. 1, pp. 313-326, 2016