The Experts below are selected from a list of 720 Experts worldwide ranked by ideXlab platform
Gerhard Holzapfel - One of the best experts on this subject based on the ideXlab platform.
-
a theoretical model for fibroblast controlled growth of Saccular Cerebral Aneurysms
Journal of Theoretical Biology, 2009Co-Authors: Martin Kroon, Gerhard HolzapfelAbstract:A new theoretical model for the growth of Saccular Cerebral Aneurysms is proposed by extending the recent constitutive framework of Kroon and Holzapfel [2007a. A model for Saccular Cerebral aneurysm growth by collagen fibre remodelling. J. Theor. Biol. 247, 775-787]. The continuous turnover of collagen is taken to be the driving mechanism in aneurysmal growth. The collagen production rate depends on the magnitude of the cyclic deformation of fibroblasts, caused by the pulsating blood pressure during the cardiac cycle. The volume density of fibroblasts in the aneurysmal tissue is taken to be constant throughout the growth process. The growth model is assessed by considering the inflation of an axisymmetric membranous piece of aneurysmal tissue, with material characteristics representative of a Cerebral aneurysm. The diastolic and systolic states of the aneurysm are computed, together with its load-free state. It turns out that the value of collagen pre-stretch, that determines growth speed and stability of the aneurysm, is of pivotal importance. The model is able to predict Aneurysms with typical berry-like shapes observed clinically, and the predicted wall stresses correlate well with the experimentally obtained ultimate stresses of this type of tissue. The model predicts that Aneurysms should fail when reaching a size of about 1.2-3.6mm, which is smaller than what has been clinically observed. With some refinements, the model may, however, be used to predict future growth of diagnosed Aneurysms.
-
estimation of the distributions of anisotropic elastic properties and wall stresses of Saccular Cerebral Aneurysms by inverse analysis
Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 2008Co-Authors: Martin Kroon, Gerhard HolzapfelAbstract:A new method is proposed for estimating the elastic properties of the inhomogeneous and anisotropic structure of Saccular Cerebral Aneurysms by inverse analysis. The aneurysm is modelled as a membrane and the constitutive response of each individual layer of the passive tissue is characterized by a transversely isotropic strain energy function of exponential type. The collagen fibres in the aneurysm wall are assumed to govern the mechanical response. Four parameters characterize the constitutive behaviour of the tissue: two initial stiffnesses of the collagen fabric in the two in-plane principal directions, one parameter describing the degree of nonlinearity that the collagen fibres exhibit and the other structural parameter, i.e. the angle which defines the orientation of the collagen fibres. The parameter describing the fibre nonlinearity is assumed to be constant, while all others are assumed to vary continuously over the aneurysm surface. Two model Aneurysms, with the same initial geometry, boundary and loading conditions, constitutive behaviour and finite-element discretization, are defined: a ‘reference model’ with known distributions of material and structural properties and an ‘estimation model’ whose properties are to be estimated. An error function is defined quantifying the deviations between the deformations from the reference and the estimation models. The error function is minimized with respect to the unknown parameters in the estimation model, and in this way the reference parameter distributions are re-established. In order to achieve a robust parameter estimation, a novel element partition method is employed. The accordance between the estimated and the reference distributions is satisfactory. The deviations of the maximum stress distributions between the two models are below 1%. Consequently, the wall stresses in the Cerebral aneurysm estimated by inverse analysis are accurate enough to facilitate the assessment of the risk of aneurysm rupture.
Takamasa Kayama - One of the best experts on this subject based on the ideXlab platform.
-
wall enhancement of the intracranial Aneurysms revealed by magnetic resonance vessel wall imaging using three dimensional turbo spin echo sequence with motion sensitized driven equilibrium a sign of ruptured aneurysm
Clinical Neuroradiology-klinische Neuroradiologie, 2016Co-Authors: S Nagahata, M Nagahata, Makoto Obara, Rei Kondo, N Minagawa, S Sato, W Mouri, S Saito, Takamasa KayamaAbstract:Purpose Wall enhancement of Saccular Cerebral Aneurysms has not been researched sufficiently. Our purpose of this study was to investigate the incidence of aneurysmal wall enhancement by the three-dimensional turbo spin-echo sequence with motion-sensitized driven equilibrium (MSDE-3D-TSE) imaging after gadolinium injection.
-
wall enhancement of the intracranial Aneurysms revealed by magnetic resonance vessel wall imaging using three dimensional turbo spin echo sequence with motion sensitized driven equilibrium a sign of ruptured aneurysm
Clinical Neuroradiology-klinische Neuroradiologie, 2016Co-Authors: S Nagahata, M Nagahata, Makoto Obara, Rei Kondo, N Minagawa, S Sato, W Mouri, S Saito, Takamasa KayamaAbstract:Wall enhancement of Saccular Cerebral Aneurysms has not been researched sufficiently. Our purpose of this study was to investigate the incidence of aneurysmal wall enhancement by the three-dimensional turbo spin-echo sequence with motion-sensitized driven equilibrium (MSDE-3D-TSE) imaging after gadolinium injection. We retrospectively reviewed the pre- and postcontrast MSDE-3D-TSE images of 117 consecutive patients with intracranial Aneurysms from September 2011 to July 2013. A total of 61 ruptured and 83 unruptured Aneurysms of 61 patients with subarachnoid hemorrhage (SAH) and 56 non-SAH patients were enrolled in this study. We evaluated the wall enhancement of each aneurysm on postcontrast MSDE-3D-TSE images compared with precontrast images. We classified the aneurysmal wall enhancement into three groups as “Strong enhancement,” “Faint enhancement,” and “No enhancement.” “Strong/Faint enhancement” of the aneurysm was detected in 73.8/24.6 % of the ruptured Aneurysms and 4.8/13.3 % of the unruptured Aneurysms. “No enhancement” was found in 1.6 % of the ruptured Aneurysms and 81.9 % of the unruptured Aneurysms. By magnetic resonance vessel wall imaging using the MSDE-3D-TSE sequence, wall enhancement was frequently observed on ruptured Aneurysms. Therefore, aneurysmal wall enhancement may be an indicator of the ruptured condition, which is useful information for managing patients with SAH.
Yiannis Ventikos - One of the best experts on this subject based on the ideXlab platform.
-
Modelling evolution and the evolving mechanical environment of Saccular Cerebral Aneurysms
Biomechanics and modeling in mechanobiology, 2010Co-Authors: Paul N. Watton, Alisa Selimovic, Nikolaus B. Raberger, P. Huang, Gerhard A. Holzapfel, Yiannis VentikosAbstract:A fluid–solid-growth (FSG) model of Saccular Cerebral aneurysm evolution is developed. It utilises a realistic two-layered structural model of the internal carotid artery and explicitly accounts for the degradation of the elastinous constituents and growth and remodelling (GR the collagen fabric adapts, and the artery achieves a new homeostatic configuration. The perturbation to the geometry creates an altered haemodynamic environment. Subsequent degradation of elastin is explicitly linked to low wall shear stress (WSS) in a confined region of the arterial domain. A sidewall Saccular aneurysm develops, the collagen fabric adapts and the aneurysm stabilises in size. A quasi-static analysis is performed to determine the geometry at diastolic pressure. This enables the cyclic stretching of the tissue to be quantified, and we propose a novel index to quantify the degree of biaxial stretching of the tissue. Whilst growth is linked to low WSS from a steady (systolic) flow analysis, a pulsatile flow analysis is performed to compare steady and pulsatile flow parameters during evolution. This model illustrates the evolving mechanical environment for an idealised Saccular Cerebral aneurysm developing on a cylindrical parent artery and provides the guidance to more sophisticated FSG models of aneurysm evolution which link G&R to the local mechanical stimuli of vascular cells.
-
modelling evolution of Saccular Cerebral Aneurysms
Journal of Strain Analysis for Engineering Design, 2009Co-Authors: Paul N. Watton, Yiannis VentikosAbstract:A computational model for the evolution of a Saccular Cerebral aneurysm of the internal carotid artery is developed. The artery is modelled as a two-layered non-linear elastic cylindrical membrane using a physiologically realistic constitutive model. It is subject to a constant systolic pressure and a physiological axial prestretch. The development of the aneurysm is assumed to be a consequence of the growth and remodelling of its material constituents. The elastinous constituents are prescribed to degrade in a localized circular patch. Microstructural recruitment and fibre concentration variables for the collagen fibres enable the growth and remodelling of collagen fabric to be simulated. The model predicts realistic Saccular aneurysm geometries that stabilize in size. It provides the foundations for the development of more sophisticated models of Cerebral aneurysm evolution.
S Nagahata - One of the best experts on this subject based on the ideXlab platform.
-
wall enhancement of the intracranial Aneurysms revealed by magnetic resonance vessel wall imaging using three dimensional turbo spin echo sequence with motion sensitized driven equilibrium a sign of ruptured aneurysm
Clinical Neuroradiology-klinische Neuroradiologie, 2016Co-Authors: S Nagahata, M Nagahata, Makoto Obara, Rei Kondo, N Minagawa, S Sato, W Mouri, S Saito, Takamasa KayamaAbstract:Purpose Wall enhancement of Saccular Cerebral Aneurysms has not been researched sufficiently. Our purpose of this study was to investigate the incidence of aneurysmal wall enhancement by the three-dimensional turbo spin-echo sequence with motion-sensitized driven equilibrium (MSDE-3D-TSE) imaging after gadolinium injection.
-
wall enhancement of the intracranial Aneurysms revealed by magnetic resonance vessel wall imaging using three dimensional turbo spin echo sequence with motion sensitized driven equilibrium a sign of ruptured aneurysm
Clinical Neuroradiology-klinische Neuroradiologie, 2016Co-Authors: S Nagahata, M Nagahata, Makoto Obara, Rei Kondo, N Minagawa, S Sato, W Mouri, S Saito, Takamasa KayamaAbstract:Wall enhancement of Saccular Cerebral Aneurysms has not been researched sufficiently. Our purpose of this study was to investigate the incidence of aneurysmal wall enhancement by the three-dimensional turbo spin-echo sequence with motion-sensitized driven equilibrium (MSDE-3D-TSE) imaging after gadolinium injection. We retrospectively reviewed the pre- and postcontrast MSDE-3D-TSE images of 117 consecutive patients with intracranial Aneurysms from September 2011 to July 2013. A total of 61 ruptured and 83 unruptured Aneurysms of 61 patients with subarachnoid hemorrhage (SAH) and 56 non-SAH patients were enrolled in this study. We evaluated the wall enhancement of each aneurysm on postcontrast MSDE-3D-TSE images compared with precontrast images. We classified the aneurysmal wall enhancement into three groups as “Strong enhancement,” “Faint enhancement,” and “No enhancement.” “Strong/Faint enhancement” of the aneurysm was detected in 73.8/24.6 % of the ruptured Aneurysms and 4.8/13.3 % of the unruptured Aneurysms. “No enhancement” was found in 1.6 % of the ruptured Aneurysms and 81.9 % of the unruptured Aneurysms. By magnetic resonance vessel wall imaging using the MSDE-3D-TSE sequence, wall enhancement was frequently observed on ruptured Aneurysms. Therefore, aneurysmal wall enhancement may be an indicator of the ruptured condition, which is useful information for managing patients with SAH.
Robert D Brown - One of the best experts on this subject based on the ideXlab platform.
-
guglielmi detachable coil treatment of ruptured Saccular Cerebral Aneurysms retrospective review of a 10 year single center experience
American Journal of Neuroradiology, 2003Co-Authors: Jonathan A Friedman, Douglas A Nichols, Fredric B Meyer, Mark A Pichelmann, Jon I Mciver, Gerard L Toussaint, Patsy L Axley, Robert D BrownAbstract:BACKGROUND AND PURPOSE: We retrospectively analyzed our results with Guglielmi detachable coils (GDCs) for the endovascular occlusion of acutely ruptured Saccular Cerebral Aneurysms over 10 years. METHODS: Between 1991–2000, 83 patients (mean age, 56.1 years) with aneurysmal subarachnoid hemorrhage were treated with endovascular GDCs. Patients with Aneurysms due to trauma or dissection and those with mycotic or fusiform Aneurysms were excluded. Mean follow-up in survivors was 19.1 months, and the mean Hunt-Hess grade at admission was 2.2. Angiographic follow-up was performed in 93% of surviving patients (mean interval, 11.6 months). The basilar caput (34 patients) and anterior communicating artery complex (19 patients) were most commonly treated. RESULTS: Sixty-four patients (77%) had a Glasgow Outcome Scale score (GOS) of 4 or 5, nine (11%) had a score of 2 or 3, and 10 (12%) died. At follow-up, 24 patients (35%) had complete aneurysm occlusion, 18 (26%) had a dog-ear remnant, 24 (35%) had a residual neck, and two (3%) had residual aneurysm filling. No treated aneurysm rebled. Three patients required surgical repair after incomplete endovascular treatment. Two or more GDC occlusion procedures were required in 28 patients (34%). Major procedural complications occurred in two patients (2%), resulting in serious neurologic disability or death. CONCLUSION: Endovascular treatment of ruptured Cerebral Aneurysms with GDCs has low morbidity, and it facilitates good overall outcomes in patients after subarachnoid hemorrhage. The short-term effectiveness of GDC occlusion in preventing aneurysmal rebleeding was excellent. Durability of the treatment in preventing long-term rebleeding as compared with direct surgical clipping warrants further study. Advances in device technology and technique may improve future outcomes.
