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1

Numerical simulations of the pulsatile blood flow in the different types of arterial fenestrations: Comparable analysis of multiple vascular geometries

Tyfa Z., Obidowski D., Reorowicz P., Stefańczyk L., Fortuniak J., Jóźwik K.

Biocybernetics and Biomedical Engineering

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2018

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Vol. 38, no. 2

228--242

EN

In medical terms, fenestration stands for an anomaly within the circulatory system in which the blood vessel lumen is divided into two separate channels that rejoin in the distal part of this vessel. The primary objective of this research was to analyze the impact of the left vertebral artery (LVA) and basilar artery (BA) fenestrations on the blood flow characteristics in their regions and downstream, in the cerebral circulation. The geometrical data, obtained from the angio-Computed Tomography, were the basis for the generation of a 3D model in SolidWorks 2015. In order to observe the flow characteristics within the whole spatial domain, computational fluid dynamics was involved in performing simulations of the blood flow in the patient-specific arterial system (beginning with the aortic arch and finishing with the Circle of Willis). To examine the flow distribution changes resulting from altered fenestration geometries, additional models were built. The blood flow velocity, volume flow rate and shear stress distribution were analyzed within this study. It was proven that the length/size/ position of the fenestration altered the flow characteristics in different manners. The investigations showed that the patient-specific LVA, at the V3 section (extracranial part of the artery located between the spine and the skull), is not a reason of aneurysm formation. However, BA fenestration at the proximal segment might be a possible reason of future aneurysm formation. It was proven that the computational fluid dynamics tool could support medical diagnostic procedures and multivessel brain vascular disease treatment planning.

2

Reversed Robin Hood syndrome in the light of nonlinear model of cerebral circulation

Piechna A., Cieslicki K.

International Journal of Applied Mechanics and Engineering

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2017

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Vol. 22, no. 2

459--464

EN

The brain is supplied by the internal carotid and vertebro-basilar systems of vessels interconnected by arterial anastomoses and forming at the base of the brain a structure called the Circle of Willis (CoW). An active intrinsic ability of cerebral vascular bed maintains constant Cerebral Blood Flow (CBF) in a certain range of systemic pressure changes. This ability is called autoregulation and together with the redundant structure of the CoW guarantee maintaining CBF even in partial occlusion of supplying arteries. However, there are some situations when the combination of those two mechanisms causes an opposite effect called the Reversed Robin Hood Syndrome (RRHS). In this work we proposed a model of the CoW with autoregulation mechanism and investigated a RRHS which may occur in the case of Internal Carotid Artery (ICA) stenosis combined with hypercapnia. We showed and analyzed the mechanism of stealing the blood by the contralateral side of the brain. Our results were qualitatively compared with the clinical reports available in the literature.

3

Ocena morfometryczna podziału środkowych tętnic mózgowych prawidłowych i z tętniakiem

Kawlewska E., Hehnel N., Wolański W., Ćmiel-Smorzyk K., Kaspera W.

Aktualne Problemy Biomechaniki

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2016

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z. 11

53--58

PL

W artykule przeprowadzono analizę morfologiczną tętnic środkowych mózgu w miejscu podziału na tętnicę skroniową i czołową. Trójwymiarowe modele tętnic pacjentów zostały wygenerowane w środowisku Mimics na podstawie zdjęć angioTK. Analizowano tętnice 24 pacjentów z tętniakiem oraz 24 pacjentów zdrowych, u których badanie angioTK wykonano w ramach rutynowej diagnozy innych schorzeń. Uzyskaną bazę danych podsumowano metodami statystki opisowej, porównywano m.in. średnie wartości pól przekrojów, obwodów i średnic poszczególnych naczyń, a także kąty pomiędzy tętnicami. Praca stanowi podstawę do dalszej wielowymiarowej analizy statystycznej.

EN

In this paper it was performed the morphological analysis of bifurcation geometry in middle cerebral arteries. The three-dimensional models of arteries were obtained from angiography images from 24 healthy people and 24 patients with aneurysm. There were analyzed the mean values and quartiles of diameters, areas, circumferences and angles. It was also calculated kurtosis, to check whether the distribution is normal. The studies are the basis for further, multivariate statistical analysis.

4

Modeling of human circle of Willis with and without aneurisms

Ivanov D., Dol A., Pavlova O., Aristambekova A.

Acta of Bioengineering and Biomechanics

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2014

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Vol. 16, no. 2

121--129

EN

Purpose: This paper includes results of the first stage of research aimed at the development of recommendations for physicians in order to help them to choose a particular type of cerebral arteries aneurysms treatment. Methods: Recent studies show that the majority of aneurysms develop as a result of hemodynamic and degenerative lesions of the vascular wall. Obviously, such wall damage can be studied using the methods of continuum mechanics and numerical simulations. Biomechanical modelling allows us to study hemodynamic parameters and stress-strain state of these arteries in health and disease, and to formulate practical recommendations for the necessity and reasonable selection of a particular type of cerebral arteries aneurysm treatment. Results: At this stage the realistic geometric models of arterial circle of Willis were built for its normal state and in the presence of aneurysms. The ultrasound analysis of circle of Willis was conducted in order to obtain blood flow parameters and the boundary conditions for carotid and vertebral arteries. Also, the mechanical properties of these arteries were investigated and constants of the Mooney–Rivlin strain energy function were obtained. Conclusions: Thus, the boundary problem describing the behaviour of human Willis circle arteries was stated. Further, this problem will be solved numerically using the finite element method. The numerical results will be analyzed from the point of view of the influence of the mechanical factors on the emergence, growth and rupture of circle of Willis aneurysms.

5

Numerical Study of a Flow in the Cerebral Arterial Circle

Obidowski D., Jozwik K., Reorowicz P.

Computer Methods in Materials Science

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2009

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Vol. 9, No. 1

79-84

EN

Blood is supplied to the brain by two internal carotid and two vertebral arteries. These arteries join to form the cerebral arterial circle (also called the Circle of Willis or CoW). This unique arrangement of human vessels ensures blood supply to the brain despite of any pathology in the geometry of arteries supplying the brain. Computed Tomography was used in this case for imagining the CoW as well as the arteries supplying it. The images obtained during the test were used to develop numerical model of one particular patient?s vessels geometry. Finally, with the use of numerical methods it is possible to simulate a realistic flow within the region where no other method can be used and thus one can analyze an influence of the pathological narrowing onto the cerebral perfusion. Using Computed Tomography large series of two-dimensional X-ray images were taken along the patient's axis during one test. The distance between single images is 0.6 mm. Vessels as they are soft tissues have to be visualized by contrast. Having these images, a three-dimensional path of the single artery was studied and its geometry was generated in CAD software (SolidWorks). Then, 3D mesh was generated using CFX Mesh code. Numerical experiment was carried out for different velocities within the physiological range. Blood was modeled as a Newtonian fluid.

PL

Głównymi tętnicami dostarczającymi krew do mózgu są dwie tętnice szyjne wewnętrzne oraz dwie tętnice kręgowe. Naczynia te łączą się w jamie czaszki tworząc koło tętnicze mózgu (koło Willisa). Układ ten ma za zadanie zapewnienie prawidłowego ukrwienia mózgu bez względu na zmiany patologiczne w geometrii naczyń zasilających mózg. W pracy tej posłużono się komputerową tomografią,jako sposobem obrazowania naczyń krwionośnych. Zastosowanie obrazów z TK pozwoliło na zbudowanie modelu numerycznego koła Willisa dla indywidualnego przypadku danego pacjenta. W chwili obecnej posługując się metodami numerycznymi możliwe jest odtworzenie rzeczywistego przepływu w obszarze, jak i zbadać wpływ anomalii w budowie na ukrwienie mózgu. Podstawą do zbudowania modelu były serie obrazów pozyskanych w czasie badania badania z wykorzystaniem tomografii komputerowej. W metodzie tej generowany jest obraz 2D na płaszczyznach prostopadłych do głównej osi pacjenta. Płaszczyzny oddalone są od siebie o 0,6 [mm]. Dla uwidocznienia naczyń krwionośnych, które są tkanką miękką, dodano środka kontrastowego. Na podstawie tych obrazów odwzorowano trójwymiarową ścieżkę osi każdego z kanałów. Kolejnym etapem było przeniesienie danych do programu SolidWorks. Następnie wygenerowana została siatka przestrzenna, do wykonania której wykorzystano oprogramowanie CFX Mesh. Symulacje przeprowadzone zostały dla różnych charakterystycznych wartości prędkości z zakresu prędkości fizjologicznych występujących w układzie krwionośnym. Krew została zdefiniowana jako ciecz Newtonowska.

6

Symulacje przepływu w kole tętniczym mózgu

Obidowski D., Jóźwik K., Reorewicz P.

Zeszyty Naukowe. Cieplne Maszyny Przepływowe - Turbomachinery / Politechnika Łódzka

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2008

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nr 134

35-42

PL

Główne tętnice zasilające mózg - dwie symetryczne tętnice szyjne oraz dwie symetryczne tętnice kręgowe wchodzące do czaszki przez otwór wielki, a następnie łączące się w tętnice podstawną - tworzą połączenie, które nosi nazwę koła Willisa (koło tętnicze mózgu). Jako podstawę do tworzenia indywidualnych geometrii układu, użyto badań tomografii komputerowej (TK). Zastosowano nienewtonowski model krwi. W pracy przedstawiono wyniki symulacji przepływu w modelowanym układzie pozwalające na ocenę rozpływu krwi do poszczególnych naczyń.

EN

The main arteries - a pair of carotid arteries and a pair of vertebral arteries entering the skull, join together to form a basilar artery. All of them create an arterial connection called the Circle of Willis (cerebral arterial circle). This unique arterial system was reconstructed with the use of Computer Tomography images. Blood was modelled as a non-Newtonian fluid. Results of the numerical experiment showing the blood outflow to cerebral arteries from arterial circle are presented in the paper.

7

Experimental and numerical modelling of flow in the human cerebral arteries

Cieślicki K.

Journal of Medical Informatics & Technologies

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2004

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Vol. 7

IP17--26

EN

The paper presents the results of experiments concerning flow in the model of cerebral supplying arteries and the Circle of Willis (CW). Vascular phantom was prepared on the basis of anatomical specimens. The most typical artery shapes and dimensions were considered. Pressure distribution in 6 characteristic points is provided, and so are the average flow rates in the anterior, middle and posterior section of the brain. Tests were run in the conditions replicating the physiological state (i.e. when the supplying arteries were fully patent) and in pathological conditions, in which the internal carotid and vertebral arteries were occluded on one or both sides. Thus obtained results were compared with the results of computer simulations based on linear and non-linear flow models. To estimate the non-linear resistance of vascular segment two phenomenological formulae were proposed. High degree of correlation between the values obtained from experiments and those registered in non-linear computer model proves usefulness of proposed formulae. It verifies the hypothesis that nonlinearity of flow characteristics of the vessel segments is to a great extent caused by their tortuous and small length in relation to diameter. Non-linear effects are particularly pronounced in conditions of pathological occlusion of supplying vessels.