Biomedical Engineering Reference
In-Depth Information
13.4.2 Unsteady blood flow in a compliant femoral bypass
For this test case, the geometric model of the distal anastomosis of a femoral bypass
is obtained through a 3T MRI scanner of the left lower limb of a patient. The lumen
geometry is subsequently reconstructed in 3D from the raw medical images using
the open source software 3D slicer (see Fig. 13.11). The vascular wall is obtained
by extruding the lumen surface in the outward normal direction with a given wall
thickness of
h
of a tenth of the vessel radius.This extruded volume is then divided in
4 layers (see white volume in Figs. 13.11b and 13.11c).
For the meshing of the lumen volume (see red volume in Fig. 13.11b), we have
considered different tetrahedral meshes: three fully unstructured meshes and three
meshes with a fluid boundary layer (see table 13.2). We have considered three
different mesh sizes
h
fine
,
h
medium
and
h
coarse
that are such that
h
coarse
/
h
medium
=
h
medium
/
2.
The boundary conditions imposed at the inlet-outlet of the vessel are patient-
specific measured flow rates (Fig. 13.11b), while an homogeneous Dirichlet con-
dition is imposed on the occluded branch. The flow rate is imposed through a La-
grange multiplier as defective boundary conditions [15]. The Young modulus and
Poisson coefficient characterizing the elastic material modelling the arterial wall
are respectively
E
h
fine
=
10
6
dyne
cm
2
=
4
·
/
and
ν
=
0
.
45. The fluid dynamic viscosity
(a)
(b)
(c)
Fig. 13.11.
Segmentation of the arteries of the left lower limb of a patient with a venous graft that
bypasses the occluded femoral artery. We have focused on the geometry of the distal anastomosis.
Two different type of meshes are considered for the lumen volume (in red): b) meshes with a viscous
boundary layer (BL meshes) and c) fully unstructured tetrahedral meshes (U meshes). The mesh of
the vascular wall is colored in white. The presented meshes are of middle mesh size (see Table 13.2)
