came - expertverlag.de · between august 2009 and february 2010, were identified and their data...

1| 2011

2. JahrgangISSN 2190-0698

cameComputer Aided Medical Engineering

A. Marzo, D. Sweeney, M. Murphy

Computer Modelling of Haemodynamics and Morphology in Patient-Specific Intracranial Aneurysms

C. Wyss

Muscle Modelling und FEM-Einsatzin der Fusschirurgie

C. Bourauel, A. Rahimi, L. Keilig, S. Reimann, I. Hasan, M. Abboud, G. Wahl

Biomechanik sofortbelasteter Dentalimplantate

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D. van den Heever, C. Mueller, C. SchefferPatienten-spezifisches Design von Knie-Implantaten

A. Marzo, D. Sweeney, M. MurphyComputer Modelling of Haemodynamics and Morphologyin Patient-Specific Intracranial Aneurysms

B. Trachet, D. Devos, J. De Backer, A. De Paepe, B. L. Loeys, P. SegersPatienten-spezifisches Modell der Wandschubspannung von Aortenbogen

2. Jahrgang . 1 | 2011 3Computer Aided Medical Engineering

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TitelEntwurf und Gestaltung: Ludwig-Kirn Layout, LudwigsburgBild: FE-Modell eines Fußes von Dr. med. Christian Wyss

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C. Bourauel, A. Rahimi, L. Keilig, S. Reimann, I. Hasan, M. Abboud, G. Wahl Experimentelle und numerische Analyse des biomechani-schen Verhaltens sofortbelasteter Dentalimplantate im Schweinemodell

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Introduction

Aneurysms are abnormal dilations in a

blood vessel, carrying an inherent risk of

rupture and haemorrhage with devastating,

life-threatening consequences. Current

management is mostly decided upon size

of the aneurysmal sac with often contro-

versial outcome [1].

Although what causes an aneurysm re-

mains unclear, there is a growing consen-

sus on the important role played by hae-

modynamics and their morphology with

respect to their formation, growth and rup-

ture. Measuring shape and blood flow in

vivo is possible, e.g. using magnetic reso-

nance imaging (MRI), however inherent

limitations in the current technology result

in poor resolution and unsatisfactory re-

sults for smaller aneurysms.

In collaboration with the EU multidiscipli-

nary project @neurIST (www.aneurist.org),

IDAC Ireland Ltd developed a set of web-

based applications to optimize the use of

clinical data and automatically extract re-

levant blood flow and shape information

that may have relevance in IA develop-

ment. These are tools based on CFD and

other numerical techniques to automati-

cally and non-invasively extract these phy-

sical indices from the patient-specific geo-

metries. This study used the IDAC web-

based processing chain and compared the

performance of the @neurIST indices with

the traditional diagnostic indices in identi-

fying aneurism at greater risk of rupture.

Materials and methods

The study was conducted as a co-operation

between the Departments of Neurosurgery,

2. Jahrgang . 1 | 201124

Computer Modelling ofHaemodynamics and Morphologyin Patient-Specific Intracranial Aneurysmsvon A. Marzo, D. Sweeney, M. Murphy

*

Dr. Alberto MarzoDepartment of Cardiovascular Science, University of Sheffield, Sheffield, UKDerek Sweeney, BE,IDAC Ireland Ltd, Dublin, IrelandMr. Martin Murphy, MRCSI Department of Neurosurgery, Beaumont Hospital,Dublin, Ireland

Abstract

Haemodynamics and morphology are be-

lieved to play an important role in the de-

velopment and rupture of intracranial an-

eurysms (IAs). A technology based on

Computational Fluid Dynamics (CFD)

and morphological algorithms, was used to

extract haemodynamic and shape data

from the neurological images of 10 pa-

tients affected by IA. Results indicate that

some physical parameters are strongly cor-

related with the event of rupture and may

perform better than the indicators used in

current clinical management in identifying

IAs at higher risk. Oscillatory Shear Index

(OSI) and Non-sphericity Index (NSI)

showed the strongest correlation with an-

eurysm rupture.

Keywords

Patient-specific Simulation, CFD, Cere-

bral Aneurysm

Beaumont Hospital, Dublin, Ireland, and

the Department of Cardiovascular Scien-

ce, University of Sheffield, Sheffield, UK.

A total of 10 patients diagnosed with IA

between August 2009 and February 2010,

were identified and their data collected

upon appropriate ethical approval and pa-

tient consent. Table 1 gives the demogra-

phic constitution of the population along

with the relevant aneurysm details.

The vessel geometries were extracted from

3D rotational acquisition (3DRA). The

@neurIST technology, available through

the idacapps web-based applications

(www.idacireland.com), was used to seg-

ment, extract and repair the vessel surfa-

ces. In particular, vessel triangular surfaces

were created using a threshold isosurface

extraction tool, based on the marching cu-

bes algorithm. During vessel recon-

struction, the neck of the aneurysms was

manually identified and marked to define

the aneurysmal sac that was used for the

haemodynamic and morphological cha-

racterisation of each aneurysm. Volumetric

meshes were generated using ANSYS

ICEM CFD 11.0. Grids were made finer at

the walls and progressively coarser to-

wards the vessel axis. Tetrahedral ele-

ments were used for the discretisation of

the domain core, with three layers of pris-

matic elements adjacent to the wall, thus

ensuring accurate computation of haemo-

dynamic stresses at the wall. Element size

and number were set accordingly to the

outcome of a mesh dependency study per-

formed on similar aneurysmal geometries

[3]. The 3D unsteady Navier–Stokes

equations were solved by using the finite-

control-volume software, ANSYS-CFX.

Blood was assumed to be incompressible,

with density ρ =1 050 kg/m

3

and Newto-

Computer Aided Medical Engineering

caMe_1_11 31.03.2011 17:03 Uhr Seite 24

nian, with viscosity μ = 0.0035 Pa s. All

analyses were run on the Amazon EC2

cloud computing resource, The High Me-

mory Double Extra Large Instance (34 GB

RAM, 4 virtual cores, 3.25 GHz). The

average time required to solve one cardi-

ac cycle with the meshes considered was

approximately 4 hours. Boundary condi-

tions were provided by the use of a 1D

model of the cardiovascular system, re-

producing typical pressure and flow rate

waveforms [4]. Indices such as Wall She-

ar Stress (WSS) and Oscillatory Shear In-

dex (OSI, values 0 < OSI < 0.5), a varia-

ble measuring the oscillatory behaviour of

viscous forces at the wall, were computed

for their known influence on arterial

physiology.

Basic morphological indices were auto-

matically computed for the aneurysmal

dome. These included aspect ratio (AR),

i.e. ratio between aneurysm depth and

neck width, size ratio (SR), which relates

aneurysm size with parent vessel size,

and NSI, which relates aneurysm volume

and surface area. NSI quantifies the irre-

gularity of the aneurysmal surface

(NSI = 0 spherical surfaces, NS I≠ 0 irre-

gular surface)


2. Jahrgang . 1 | 2011 25Computer Aided Medical Engineering

aneurysm age hemisphere location size status

1 59 center Basilar 4 unruptured

2 59 right PComA 3 ruptured


4 35 right PComA 3 unruptured

5 42 center Basilar 10 ruptured

6 35 right ICA 3 ruptured

7 66 left PComA 10 ruptured

8 67 left PComA 6 ruptured


10 60 left PComA 7 unruptured

Legend - PComA = Posterior Communicating Artery, ICA = Internal Carotid Artery.

Table 1: Patient demographics and aneurysm radiological features

Aneurysm 1

Aneurysm 6

Aneurysm 2

Aneurysm 7

Aneurysm 3

Aneurysm 8

Aneurysm 4

Aneurysm 9

Aneurysm 5

Aneurysm 10

Figure 1: Surface geometries of the aneurysms and their surrounding vasculature

Table 2: Haemodynamic indices. Areas are reported as percentage of the totalaneurysm surface area

aneurysm area WSS<0.4 Pa Max OSI area elevated OSI status

1 0 0.32 0.7 unruptured

2 11.4 0.47 7.7 ruptured

3 0 0.38 4.5 ruptured


5 59.4 0.44 4 ruptured

6 0 0.48 24.1 ruptured

7 7.4 0.41 3.4 ruptured

8 5.6 0.42 1.2 ruptured

9 0 0.44 3.0 ruptured


Results

Table 2 shows the max values of OSI and

the extension of the areas affected by high

OSI as a percentage of the total surface

area of the aneurysmal sac. Shear forces

are highly oscillatory for aneurysms 2, 5-

9. Relatively lower values were predicted

for aneurysms 1, 3, 4, 10.

In the same table are reported the percen-

tage areas affected by infra-physiological

WSS (< 0.4 Pa). Areas exposed to low

WSS were predicted for aneurysms 2, 5, 7

and 8.

caMe_1_11 31.03.2011 17:03 Uhr Seite 25

performance 6/7). The @neurIST compu-

tational tool-chain is the result of a multi-

disciplinary effort and the feedback recei-

ved on the many exposures of the softwa-

re to the clinical and scientific communi-

ty [5]. The analyses of this study were

processed by a clinical scientist and a

Neurosurgeon trained on the use of the

computational tools. Their performance

was compared and results were interchan-

geable within 5 cases, thus demonstrating

the ease of use of the tools by a non-expert

user.

Acknowledgements

The @neurIST Project was funded by the

European Commission, VI Framework

Program, Priority 2, Information Society

Computational Intelligence and Neuros-

cience Technologies, a European Public

Funded Organization (Research Grant no.

IST-FP6-027703).

References

[1] „Unruptured intracranial aneurysms-risk of

rupture and risks of surgical intervention. Inter-

national Study of Unruptured Intracranial An-

eurysms Investigators,“ The New England

Journal of Medicine, vol. 339, pp. 1725-1733,

1998.

[2] A. M. Malek, S. L. Alper, and S. Izumo, „He-

modynamic shear stress and its role in atheros-

clerosis,“ The Journal of the AmericanMedical

Association, vol. 282, no. 21, pp. 2035–2042,

1999.

[3] A. G. Radaelli, L. Augsburger, J. R. Cebral, et

al., „Reproducibility of haemodynamical simu-

lations in a subject-specific stented aneurysm

model – a report on the Virtual Intracranial

Stenting Challenge 2007,“ Journal of Biome-

chanics, vol. 41, no.10, pp. 2069–2081, 2008.

[4] P. Reymond, F. Merenda, et al. Validation of a

one-dimensional model of the systemic arterial

tree. Am J Physiol Heart Circ Physiol, v.297,

n.1, Jul, p.H208-22. 2009.

[5] Singh PK, Marzo A, et al, „The role of compu-

tational fluid dynamics in the management of

unruptured intracranial aneurysms: a clinicians’

view,“ Comput Intell Neurosci. 2009:760364.

Epub 2009 Aug 19.


2. Jahrgang . 1 | 201126

Figure 2 shows aneurysmal

areas affected by infra-physio-

logical WSS (< 0.4 Pa) and

areas affected by high OSI.

Table 3 shows morphologi-

cal values of AR, SR and NSI.

Aneurysms 2, 5, 7-9 have high

aspect ratio, whereas aneu-

rysms 1, 4, 10 have relatively

lower values. Size ratio is high

in aneurysms 2, 4, 5, 7, and 9,

and relatively lower for aneu-

rysms 3, and 10. Finally aneu-

rysms 2, 3, 5-10 have irregular

shapes, as evidenced by their

non-sphericity index, whereas

aneurysms 1, and 4 have sha-

pes closer to a sphere.

Table 3: Morphological indices. AR = aspect ratio, SR = sixe ratio, NSI = non-sphericity index

aneurysm AR SR NSI status

1 0.92 1.5 0.09 unruptured

2 1.38 1.71 0.2 ruptured

3 0.81 0.86 0.12 ruptured

4 0.92 1.63 0.09 unruptured

5 2.09 2.36 0.29 ruptured

6 1.27 1.25 0.15 ruptured

7 2.59 2.49 0.26 ruptured

8 1.83 1.81 0.25 ruptured

9 1.88 3.09 0.29 ruptured

10 0.87 0.83 0.21 unruptured

Discussion and conclusions

Current clinical management of IAs con-

siders size as major predictor of rupture.

Treatment is often advocated if aneurysm

size is above 7mm. Table 1 clearly shows

that only 3 of the ruptured aneurysm co-

hort are above 7 mm (index performance

3/7). Index performance is considerably

higher for some of the indices computed

using the @neurIST technology. All four

aneurysms exposed to very low values of

WSS ruptured (index performance 4/7).

This is in line with the established know-

ledge that the endothelial layer (inner lay-

er of the arterial wall) is adversely affected

by low values of WSS [2]. Particularly

strong correlations were observed bet-

ween rupture and highly oscillatory shear

forces (OSI > 0.4) (index performance

6/7), aspect ratio above 1.2 (index perfor-

mance 5/7), and NSI above 0.12 (index

Figure 2 Top: surface areas affected by WSS < 0.4Pa (blue), WSS > 0.4Pa (red) for aneu-rysms 2,5, and 7. Bottom: OSI contours for aneurysms 5, 6, and 7.

Short Biography

Martin Murphy

Martin Murphy is a graduate of the UniversityCollege Cork School of Medicine and is a SpecialistRegistrar in neurosurgery. He is currently employedin Beaumont Hospital Dublin, but has also workedas a neurosurgeon both in Cork and in St Louis,USA under the supervision of Ralph Dacey, one ofthe foremost authorities in vascular neurosurgery.He has witnessed at first hand both the successfultreatment and poor outcomes associated withsubarachnoid haemorrhage. He hopes to improvepatient outcomes through succesful identification of those patients most at risk of this devastatingcondition, whilst also avoiding subjecting otherpatients to the not-insignificant risks of both surgicaland endovascular treatments.


caMe_1_11 31.03.2011 17:04 Uhr Seite 26

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1| 2011

2. JahrgangISSN 2190-0698

cameComputer Aided Medical Engineering

A. Marzo, D. Sweeney, M. Murphy


C. Wyss

Muscle Modelling und FEM-Einsatzin der Fusschirurgie

C. Bourauel, A. Rahimi, L. Keilig, S. Reimann, I. Hasan, M. Abboud, G. Wahl

Biomechanik sofortbelasteter Dentalimplantate


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