WWW.THESIS.XLIBX.INFO
FREE ELECTRONIC LIBRARY - Thesis, documentation, books
 
<< HOME
CONTACTS



Pages:   || 2 | 3 | 4 | 5 |   ...   | 15 |

«Der Technischen Fakultät der Universität Erlangen-Nürnberg zur Erlangung des Grades DOKTOR-INGENIEUR vorgelegt von Efraín López Ramírez ...»

-- [ Page 1 ] --

Numerical Investigation of Blood

Flow in Stented Intracranial

Aneurysm Models

Numerische Untersuchung der

Blutströmung durch intrakranielle

Aneurysmen mit Stents

Der Technischen Fakultät der

Universität Erlangen-Nürnberg

zur Erlangung des Grades

DOKTOR-INGENIEUR

vorgelegt von

Efraín López Ramírez

Erlangen - 2011

Als Dissertation genehmigt von

der Technischen Fakultät der

Universität Erlangen-Nürnberg

Tag der Einreichtung : 06.05.2010 Tag der Promotion : 15.02.2011 Dekan: Prof. Dr.-Ing. habil. R. German Berichterstatter: Prof. Dr.-Ing. A. Delgado Prof. Dr. rer. nat. habil. U. Rüde Acknowledgments The present dissertation thesis is the result of my research work carried out during my stay at the Institute of Fluid Mechanics (LSTM), Friedrich-Alexander University ErlangenNuremberg, Germany. This thesis would have not been possible without the financial support awarded by the National Council on Science and Technology of Mexico (CONACYT) and the German Academic Exchange Service (DAAD) to conduct my doctoral studies, this support is highly acknowledged.

I am heartily thankful to my Ph.D. supervisor Prof. Dr.-Ing. habil. Antonio Delgado Rodriguez for giving me the opportunity to work in his group and for his support, motivation and guidance throughout my research work. His technical and editorial advices were essential for the completion of my dissertation. Muchas gracias por todo el apoyo.

I am very much grateful to Prof. Dr. Dr. h.c. F. Durst for supporting my application for the scholarship that gave me the opportunity to join the LSTM and during the early stages of my stay in Germany.

I also thank Dr. Kamen Beronov, former head of the Medical application group for his guidance, helpful discussions and constructive criticism. Furthermore, I would like to extend my thanks to the members of the dissertation committee and the president of the jury for accepting this thesis.

Moreover, I would like to thank all colleagues at LSTM for the nice working atmosphere.

It was a also a big pleasure to share part of the doctoral studies and life with my friends Christoph Scheit and Elsy Arratia, and at this point I want to thank them for the lovely moments we lived together.

I would also like to take this opportunity to thank my friends I met in Erlangen like Estefania, Saúl, Fabricio, Poliana, Hesdras, Bianca, Carmen, Ramón, Anke, José Luis, José and Paloma for the wonderful friendship they offered me, you were a real support.

Quiero expresar mis más profundos y sinceros agradecimientos a mis padres por todos los años de apoyo, por todos sus consejos. Gracias por haberme impulsado siempre y por toda la dedicación puesta en mí.

A mis hermanos Mirsa, Ardelia, Simón, Rosa y Cecilia y a mi cuñnada Cecilia Durán muchas gracias por tantos momentos inovidables que hemos pasado juntos, gracias por las inagotables anécdotas que nos unen fuertemente como hermanos a pesar de la distancia. A mis sobrinos Monse, Mirsita, Manolo, Ricky y Moni, muchas gracias por ser como son y hacer de nuestras cortas visitas enormes momentos. ¡Muchas gracias Familia!

Quiero agradecer muy especialmente a mi segunda familia, Francisco y Silvia. Les agradezco infinitamente el apoyo en todo momento desde que tuve el gusto de conocerlos. A Francisco Jr. por tan elocuentes charlas y buen humor que siempre se agradecen. A mi tío Joselito y mis primos.

Sofía, gracias por estar siempre a mi lado, aún en la distancia que nos separó al inicio de esta etapa. Gracias por todo el amor y el apoyo en este tiempo que me llevó alcanzar esta meta. Tú hiciste que este tiempo del doctorado fuera maravilloso. Gracias por creer en mi y estar a mi lado. ¡Te amo!.

Abstract The present work aims to further advance the understanding of blood flow at and in cerebral aneurysms. It focuses, in particular, on hemodynamic parameters associated with the formation and rupture of lateral and terminal aneurysms. Aneurysms are abnormally wide or bulging parts of an artery. The work includes also a study of hemodynamic effects of stent-like implants for treatment of such aneurysms. It was carried out using computational tomography data from patients, software tools for medical visualization and vessel geometry reconstruction for grid generation, and commercially available software for computational fluid dynamics (CFD).

The kind of patient-specific results on mechanical and geometric parameters of the kind obtained here can be used to assist the estimation of aneurysm rupture risk as well as the medical planning of endovascular interventions for treating vessels at high risk. The present work treats, in particular, the effect of stent placement on hemodynamic parameters such as blood flow velocity and wall shear stress. To that end, “virtual stenting” is performed and its effects simulated, in synthetic but geometrically representative models of intracranial aneurysms. The effectiveness of stenting in reducing the intra-aneurysmal flow and lowering the mechanical loads on the weakened aneurysmal wall is quantified. Qualitative knowledge of hemodynamic changes in cerebral aneurysms after stenting is gained, including e.g. the strength and location of areas with low flow and shear rates or the considerable significance of mutual situation of vessel branches and aneurysm. The predictive capability of simplified numerical models of stents is estimated against representations of flow through detailed models of stents. The work carried out in this thesis allows an estimate of the technical effort of CFD modeling of real aneurysms, including their treatment with endovascular implants, as well as the kind, range, and predictive value of information to be gained from such modeling.





Kurzfassung Ziel der vorliegenden Arbeit ist die Vertiefung des Verständnisses für die Blutströmung in der Nähe und innerhalb von Gehirnaneurysmen, insbesondere für hämodynamische Parameter, welche mit der Bildung und Ruptur von lateralen und terminalen Aneurysmen in Verbindung gesetzt werden. Aneurysmen sind krankhafte Erweiterungen von arteriellen Abschnitten. Die Arbeit beinhalten darüber hinaus Studien über die hämodynamischen Effekte, die durch Stent-ähnlichen Implantaten, welche zur endovaskulären Behandlung von Gehirnaneurysmen eingesetzt oder untersucht werden, herbeigeführt werden können. Die Arbeit wurde anhand von Computertomographie-Daten realer Patienten und mithilfe von Software für medizinische Bildgebung und Gefäßgeometrie-Rekonstruktion sowie für computational fluid dynamics (CFD) durchgeführt.

Die Art von Informationen über mechanischen und geometrischen Parametern, die auch die Mehrheit der in dieser Arbeit entstandenen Ergebnisse umfasst, kann zur Unterstützung bei der Einschätzung des Ruptur-Risikos von gefährdeten Gefäßen sowie bei der medizinischen Planung ihrer endovaskulären Behandlung herangezogen werden. Die vorliegende Arbeit befasst sich insbesondere mit der Auswirkung einer Stent-Platzierung auf hämodynamische Parameter wie Blutstromgeschwindigkeit und Wandscherspannung. Dafür wird eine “virtuelle Stent-Implantation” in synthetischen aber geometrisch repräsentativen Gefäßgeometrien im Rechner modelliert und die dadurch veränderte Hämodynamik dann mit CFD simuliert.

Dabei wird die Effizienz des Implantats hinsichtlich der Reduzierung des Blutflusses und der mechanischen Wandbelastung in Aneurysmen quantitativ untersucht. Es werden qualitative Einsichten in weitere Veränderungen der Hämodynamik nach Stent-Platzierung gewonnen, wie z.B. die Stärke und Lage von Flecken mit niedriger Fluß- bzw. Scherrate oder der oft beträchtliche Einfluss der Lage eines Aneurysmas bezüglich der Krümmung benachbarter Gefäßabschnitte. Vereinfachte numerische Modelle von Stents werden gegenüber detaillierten Darstellungen der Stent-Durchströmung bezüglich ihrer Aussagekraft bewertet. Die Lehren aus dieser Arbeit, wenn betrachtet im Zusammenhang, erlauben eine gute Einschätzung des für die CFD Modellierung von realen Aneurysmen erforderlichen technischen Aufwands, sowie der Art, der Wertspanne und der Aussagekraft von Informationen, die eine solche Modellierung als Mehrwert zu bringen verspricht.

Contents

–  –  –

3.18 Alteration of wall shear stress during a cardiac cycle measured along the light-blue line (at z = 0.0002754 m) seen in the inset figure. The line was selected arbitrarily. The inset plot (top left corner) shows the distribution of WSS along this line, whereas the main plot shows the distribution starting at the proximal side of the aneurysm (using the inset image view at the center of this Figure as reference), so that highest values in this plot are found where the aneurysm joints the parent vessel. On the other hand, the highest values of WSS are found on the distal wall of the aneurysm in this view, (not shown in the main plot, but labeled in the inset plot)................. 53

3.19 Vessel and aneurysm averages WSS over one cycle and maximum values of WSS recorded at t = 0.95 s (end diastole) in the present study and values reported by Jou [43]. The numerical data can be seen in table 3.3...... 54

3.20 Time series of pressure average at the dome PD................ 54

3.21 Left: mean WSS versus the aneurysm surface area, and right: maximal WSS at diastole versus the aneurysm area reported by Jou [43] and values calculated in the present study. WSS is given in Pascals............... 56

3.22 Bivariate scattergram with regression between the aspect ratio and the WSS of the aneurysms found in the middle cerebral artery. A significant negative correlation was observed (r = −0.67). Ruptured aneurysms reported by Shojima are shown in red, while unruptured ones are in blue. The green arrow shows the result from Case II aneurysm (located at the middle cerebral aneurysm). The orange arrow shows the Case I aneurysm (at a different position)...................................... 57

3.23 Left (Case I): Point A shows an incorrect filling of the aneurysm at the distal wall due to probable thrombus presence. B is an oval-shaped filling defect.

Right (Case II):E shows what it could be a marked elongation or daughter loculus....................................... 58

3.24 Model of small-necked aneurysm in the MCA bifurcation visualized. Left:

continuous flow technique showed an oval-shaped filling defect at the medial wall. Right: improved depiction achieved with bolus injection [25]. View from above..................................... 59

3.25 Examples of small additional aneurysms missed on DSA, but perfectly detected by the 3DRA technique. Left: A very small (0.5 mm) aneurysms (arrow) in a patient with SAH caused by a ruptured middle cerebral artery aneurysm. Right: An additional intracavernous carotid artery aneurysm (arrow) to a giant ophthalmic artery aneurysm [98]................ 60

–  –  –

4.19 Velocity average inside the aneurysm as a function of time over two seconds.

Very similar to 4.18, as expected, but the porous stent is slightly more effective in reducing the velocity inside the aneurysms. In both of the plots, the P 2 ◦ stent leads to the lowest reductions. Note that the amplitude of the waves is reduced at lower velocities............................. 81

4.20 Comparison of pathlines at three stages during the cycle. A highly recirculation pattern is observed in the interior of the unstented aneurysm, while P 2 ◦, P 4 ◦ and P 4 ◦ crossed Cases presented a low flow pattern similar to the one observed in the experimental work by Moftakhar et al. in [68].

Hemodynamics into the porous and mesh Cases are more complex. Finally, the pattern of pathlines downstream the aneurysm are more similar in the unstented, porous and mesh Cases....................... 82

4.21 Comparison of velocity contours on the plane y = 0.001 and on the plane at the inlet (neck) of each aneurysm at three stages during the cycle (indicated in the top figures)................................. 84

4.22 Comparison of velocity vectors colored by the magnitude at plane y = 0.001 m (left column) and the iso-surface of iso-velocity = 0.04 m/s, ≈ 1/2 of the average velocity inside the unstented aneurysms (right column). The snapshot were taken at peak systole, time = 0.98 s and the blood flows from left to right as illustrated by the black arrows.................. 85

4.23 Velocity at the exit of the side vessel....................... 86

4.24 Time series of WSS averaged at the aneurysm sac............... 87

4.25 Time series of pressure averaged at the aneurysm sac............. 87

4.26 WSS average over one cycle along the line shown in the inset figure (at coordinate y = 0.001 m or equator of the aneurysm). Higher WSS values are found at the distal side of the neck........................ 88

–  –  –

5.6 Averaged blood velocity at the entrance of the aneurysm (“neck”) as a function of time for the unstented, single-stented and double-stented aneurysms.... 98

5.7 Spatial average of velocity at the equatorial plane of the aneurysm as a function of time..................................... 98

5.8 Visualization of flow configuration and instantaneous stream lines of the intraaneurysmal flow in unstented (top), case I (center) and case II (bottom) stent placement sac. The color bar ranges from 0 m/s (blue) to 3.2 m/s (red)... 99

5.9 WSS averaged over the aneurysm wall, where a 10-fold reduction in this scalar can be seen after stenting with the I stent device and a further reduction was achieved with the II stent device. As the scales read, the unstented case is plotted using the left scale and the values corresponding to cases I and II with stents are plotted with the scale to the right................ 100



Pages:   || 2 | 3 | 4 | 5 |   ...   | 15 |


Similar works:

«Teaching Mathematics as Storytelling Rina Zazkis and Peter Liljedahl SensePublishers TEACHING MATHEMATICS AS STORYTELLING Teaching Mathematics as Storytelling By Rina Zazkis Simon Fraser University, Canada and Peter Liljedahl Simon Fraser University, Canada SENSE PUBLISHERS ROTTERDAM / TAIPEI A C.I.P. record for this book is available from the Library of Congress. ISBN 978-90-8790-733-4 (paperback) ISBN 978-90-8790-734-1 (hardback) ISBN 978-90-8790-735-8 (e-book) Published by: Sense Publishers,...»

«G. EDWARD LEARY Utah Commissioner of Financial Institutions before Utah Association of Financial Services Homestead Resort, Midway, Utah August 26, 2005 UTAH INDUSTRIAL BANKS Good morning. As always, it is a delight to attend the Utah Association of Financial Services Convention. Thank you for extending an invitation. This morning I have an opportunity to state my thoughts on the condition of the Utah industrial banking industry. Naturally, my thoughts will be from my perspective as the chief...»

«NASA/TM-2001-211413 Examination of Automation-Induced Complacency and Individual Difference Variates Lawrence J. Prinzel III Langley Research Center, Hampton, Virginia Holly DeVries, Fred G. Freeman, and Peter Mikulka Old Dominion University, Norfolk, Virginia December 2001 The NASA STI Program Office. in Profile • Since its founding, NASA has been dedicated CONFERENCE PUBLICATION. to the advancement of aeronautics and space Collected papers from scientific and science. The NASA Scientific...»

«Seminar R&D Nuclear Malaysia 2012 (RnD12), Dewan Tun Dr. Ismail, Agensi Nuklear Malaysia, 26-28 September 2012 NATURAL RADIOACTIVITY CONTENT AND RADIONUCLIDES LECHABILITY OF BRICKS CONTAINING INDUSTRIAL WASTE Zalina Laili, Mohd Zaidi Ibrahim, Nur Azna Mahmud and Muhamat Omar Waste & Environmental Technology Division, Malaysian Nuclear Agency (Nuclear Malaysia), Bangi, 43000 Kajang, Selangor D.E., Malaysia *E-mail :liena@nuclearmalaysia.gov.my Abstract A study have been carried out using...»

«Evaluation of East Bay Municipal Utility District's Pilot of WaterSmart Home Water Reports Prepared by David L. Mitchell M.Cubed Thomas W. Chesnutt, Ph.D., CAP™ A&N Technical Services, Inc. Prepared for California Water Foundation & East Bay Municipal Utility District December 2013 EVALUATION OF EBMUD PILOT OF WATERSMART HOME WATER REPORTS TABLE OF CONTENTS EXECUTIVE SUMMARY I. INTRODUCTION II. OVERVIEW OF SNB EFFICIENCY PROGRAMS A. SOCIAL NORMS MARKETING B. STRUCTURE OF SNB EFFICIENCY...»

«Champions for Change™ APR Benchmark PET Flake to Plaque Bleeding Label Test for PET Bottles APR recognizes that packaging innovation drives the growth of bottles available for recycling and growth of supply of bottles is essential to the well being of the plastic bottle recycling industry. APR also recognizes that some innovations may create bottles that present technical challenges for recycling. This document is a preliminary screening procedure to help innovators determine potential...»

«The cohomology of automorphism groups of free groups Karen Vogtmann∗ Abstract. There are intriguing analogies between automorphism groups of finitely generated free groups and mapping class groups of surfaces on the one hand, and arithmetic groups such as GL(n, Z) on the other. We explore aspects of these analogies, focusing on cohomological properties. Each cohomological feature is studied with the aid of topological and geometric constructions closely related to the groups. These...»

«Data Consistency and Coordination for Untrusted Environments Vom Fachbereich Informatik der Technischen Universit¨t Darmstadt a genehmigte Dissertation zur Erlangung des akademischen Grades eines Doktor rerum naturalium (Dr. rer. nat.) vorgelegt von Dipl.-Inform. Matthias Majuntke geboren in Dernbach (Westerwald) Referenten: Prof. Neeraj Suri, PhD Prof. Christof Fetzer, PhD Datum der Einreichung: 18.07.2012 Datum der m¨ndlichen Pr¨fung: 21.09.2012 u u Hochschulkennziffer: D17 Darmstadt 2012...»

«CAD STANDARDS Version 2 VENUE AND PRODUCTION DRAWINGS Based upon the European Draughting Standards For Technical Communication in Theatres (TCT) Version 14C ABTT CAD Standards V2 Contents 1 Lines 1.01 Line Form 1.02 Line Widths 1.03 Border Lines 1.04 Drawing Lines 1.05 Reference Lines 1.06 Other Lines 1.07 Other Objects 1.08 Fill Lines (Hatching) 1.09 Movable Elements 1.10 New Lines 2 Text 2.01 Size 2.02 Font 2.03 Language 3 Dimensions 3.01 Dimension Lines 3.02 Leaders 4 Layers 4.01 Layer Names...»

«Roche Applied Science Technical Note No. LC 19/2004 Color Compensation The LightCycler System is able to simultaneously detect and analyze more than one Purpose of this Note color in each capillary. Due to overlap of the emission spectra of the dyes, one channel picks up signals (crosstalk) from a dye measured by another channel. This bleed-over of fluorescence signal can result in data that cannot be interpreted. To correct the bleed-over, color compensation can be applied either during an...»

«i Diss. ETH No. 20702 User-Centered Security Mechanisms for Protecting Information Sharing in the Cloud A dissertation submitted to ETH Zurich for the degree of Doctor of Sciences presented by Iulia Ion M.Sc. in Computer Science, International University in Germany born October 25, 1983 citizen of Romania accepted on the recommendation of Prof. Dr. Friedemann Mattern, examiner, ETH Zurich Prof. Dr. Marc Langheinrich, co-examiner, University of Lugano Prof. Dr. Srdjan Čapkun, co-examiner, ETH...»

«A Mathematical Model for Context and Word-Meaning Appeared in Fourth International and Interdisciplinary Conference on Modeling and Using Context, Stanford, California, June 2003, pages 369–382 Dominic Widdows Center for the Study of Language and Information, Stanford University dwiddows@csli.stanford.edu ∗ February 10, 2008 Abstract Context is vital for deciding which of the possible senses of a word is being used in a particular situation, a task known as disambiguation. Motivated by a...»





 
<<  HOME   |    CONTACTS
2016 www.thesis.xlibx.info - Thesis, documentation, books

Materials of this site are available for review, all rights belong to their respective owners.
If you do not agree with the fact that your material is placed on this site, please, email us, we will within 1-2 business days delete him.