Particle Image Velocimetry Assessment of Stent Design Influence
on Intra-Aneurysmal Flow
BARUCH B. LIEBER,
1,2
V ERONICA LIVESCU,
3
L. N. HOPKINS,
4
and AJAY K. WAKHLOO
1,2
1
Biomedical Engineering Department, University of Miami, Coral Gables, FL;
2
Department of Radiology, University of Miami,
Miami, FL;
3
Department of Mechanical andAerospace Engineering, State University of New York at Buffalo, Buffalo, NY;
and
4
Department of Neurosurgery, State University of New York at Buffalo, Buffalo, NY
(Received 9 October 2001; accepted 12 April 2002)
Abstract—Endovascular stenting appears to be an appealing
treatment modality to selected complex intracranial aneurysms.
However, stents currently used for endovascular treatment are
not specifically designed for the cerebrovasculature. Stent pa-
rameters, such as porosity and filament size, have to be care-
fully optimized for long-term successful treatment. We investi-
gated the influence of the stent filament size on the intra-
aneurysmal flow dynamics in a sidewall aneurysm model in
vitro. Three helical stents with 76% porosity but different fila-
ment sizes of 178, 153, and 127 m were studied using particle
image velocimetry. Twenty-four pulsatile flow conditions were
investigated. The results show that stenting significantly re-
duces intra-aneurysmal vorticity and the mean circulation in-
side the aneurysm is reduced to less than 3% of its value before
stenting. For constant porosity, a further reduction of the mean
circulation, up to 30% can be obtained by reducing the filament
diameter. For a constant Womersley number, this further reduc-
tion is accentuated with increase in the peak Reynolds number.
Further reduction in the mean circulation inside the aneurysm
was not achieved for the 127 m stent. With further reduction
in filament diameter, the helical stent filaments positioned
against the aneurysm neck started wavering with the flow trans-
ferring added momentum into the aneurysm. For stents of
smaller filament diameter, a supporting ultrastructure is re-
quired. © 2002 Biomedical Engineering Society.
DOI: 10.1114/1.1495867
Keywords—Hemodynamics, Intracranial aneurysms, Stents,
Endovascular, Cerebral circulation.
INTRODUCTION
Stroke is the most common life-threatening neurologi-
cal disease and the third largest cause of death in United
States, after heart disease and cancer.
2,29
About 75% of
strokes are caused by ischemia subsequent to throm-
boembolic events or stenosis due to atherosclerotic dis-
ease while the remaining are associated with subarach-
noidal hemorrhage SAH, usually due to aneurysm
rupture. SAH has an annual incidence of about one case
per 10,000 in the population.
28
50%–60% of patients
with SAH die or suffer sever morbidity, and almost half
of the survivors are unable to return to their previous
occupation due to major neuropsychological disabilities.
The mechanisms involved in aneurysm genesis and
growth are not well understood. They are uncommon in
people below 20 years of age and are very common in
older people, especially over 65 years of age. From au-
topsy studies, 0.2%–9.9% with a mean of 5% of the
general population is thought to harbor at least one
aneurysm.
13
Intracranial aneurysms occur along the main arteries
of the cerebral circulation, especially along the circle of
Willis. Aneurysms can be classified by their shape as
fusiform and saccular. Fusiform aneurysms develop as a
gradual and rarely symmetrical spindle-shaped dilatation
of a segment of an artery.
21
They total only 1% of the
intracranial aneurysms and they occur mainly in the ver-
tebrobasilar arterial system and along the internal carotid
arteries. Saccular aneurysms appear as a localized weak-
ness in the vessel wall, affecting only part of the vessel
circumference. Saccular aneurysms arising on the major
cerebral arteries at one side of the arterial segment are
called sidewall aneurysms. Most of the aneurysms are
located at the apical region of an arterial bifurcation are
generally saccular.
Diagnosis and localization of an aneurysm is not al-
ways possible, due to the fact that almost 95% are as-
ymptomatic until they rupture.
3
Small, but generally
larger aneurysms may cause pressure effects also known
as ‘‘mass’’ effects upon the adjacent cerebral structures,
resulting in symptoms and signs used for diagnosis i.e.,
very strong headaches, disturbance or partial loss of vi-
sion, hemiparesis, facial pain around the eye, numbness
of the face, enlarged pupil size. Currently, there is no
way to determine whether or not an aneurysm will rup-
ture, or which one will rupture. Accidental discoveries of
intracranial aneurysms at autopsy prove that many aneu-
rysms never rupture. Usually, cerebral aneurysms mea-
sure about 5–10 mm in diameter when rupture occurs,
Address correspondence to B. Lieber, Biomedical Engineering De-
partment, University of Miami, 1251 Memorial Drive, Coral Gables,
FL 33146. Electronic mail: blieber@miami.edu
Annals of Biomedical Engineering, Vol. 30, pp. 768–777, 2002 0090-6964/2002/306/768/10/$15.00
Printed in the USA. All rights reserved. Copyright © 2002 Biomedical Engineering Society
768