Using Porous Media Theory to Determine the Coil Volume Needed to Arrest Flow in Brain Aneurysms - Porous Media: Applications in Biological Systems and Biotechnology - page 234

embolization to contain the coil inside the sac. Placing a stent and coil reduces
flow velocity inside the sac and promotes its thrombosis [16-19].
6.4 Background
The dynamics of blood flow dynamics are an important factor in the devel-
opment and evolution of intracranial aneurysms. A number of specific hemo-
dynamic factors including wall shear stress, pressure, impingement force, flow
rate, and particle residence time have been implicated in aneurysm growth
and rupture [20]. Therefore, hemodynamic modeling of flow in intracranial
aneurysms and their arterial wall properties may help in obtaining quantita-
tive criteria for those parameters that result in expansion or rupture. Further-
more, modeling may provide valuable treatment planning by establishing the
minimal coil packing density or the type of intracranial stent that will result
in flow arrest within the sac and ultimately in its thrombosis.
6.4.1 Clinical and Experimental Studies Associated
with the Treatment of Aneurysms Using Stent
Implantation and Coil Placement
Previous studies have analyzed blood flow characteristics of an aneurysm
after endovascular treatment using coils and stents. Most of these studies
of flow in intracranial aneurysms used idealized in vitro models with rigid
walls. These idealized models cannot be directly used for relating patient-
specific hemodynamics to the treatment plan because they do not reproduce
the anatomy or mechanical behavior of the human arteries [21-26]. Yu and
Zhao [21] conducted an in vitro steady flow study on stented and nonstented
side-wall rigid aneurysms using particle image velocimetry (PIV) over a range
of Reynolds number from 200 to 1,600. The existing regions of high-wall shear
stresses (WSSs) at the distal neck were suppressed by almost 90% in stented
aneurysms.
Lieber et al. [22] performed PIV measurements to study experimentally the
influence of stent strut size and porosity on the intraneurysmal flow dynamics
in a side-wall aneurysm model. Their results showed that stents can signifi-
cantly reduce both the intraaneurysmal vorticity and the mean flow within
the aneurysm. Liou et al. [23] conducted an experimental study to investi-
gate pulsatile flow fields in a saccular brain aneurysm model using helix and
mesh stents. Their results showed that the flow features inside the aneurysm
changed substantially with the type of stent. Canton et al. [24] conducted an
in vitro study to quantify the effect of the stents by measuring the changes
in the hemodynamic forces acting on a bifurcating aneurysm model (basilar
tip configuration) after the placement of flexible neuroform stents. A digital