Biomedical Engineering Reference
In-Depth Information
Fig. 4 (a) Fluoroscopy image of a neuro-intervention procedure: a microwire (0.014
0
in diameter)
was being manipulated in the vertebral-basilar artery; (b) computer visualisation of a microwire
and a stent; (c) visualisation of an inflated balloon. VA: vertebral artery; BA: basilar artery; PCA:
posterior cerebral artery
2.2 Endovascular Device Modeling
In a typical endovascular surgery, a hollow needle punctures the lumen of a femoral
artery. After the access site is established, a sheath dilator or a catheter is inserted
into the artery. A microwire (as shown in Fig.
4
a) and a microcatheter are further
employed and advanced to the target site through the catheter lumen in neuro-
interventions. Endo-devices, such as detachable balloons, stents and coils are then
deployed for lesion treatment.
Endo-devices may be visualised by using a combination of graphic primitives
such as cylinders and cones. For example, we can represent the microwire in the
vertebal-basilar artery of Fig.
4
a by using a long and slim cylindrical tube. We can
also visualise a stent by using tubular wireframes (Fig.
4
b), and an inflated balloon
using cones and cylinders (Fig.
4
c). However, it is much more complex to simulate
the haemodynamic effects of an endo-device on the cardiovascular system because
the flow equations must be solved. In general, the effects of endo-devices on flow
patterns may be classified into three categories:
- Alteration of vessel diameters and thus flow rate, e.g., by using stents to expand
vessel lumen;
- Modification of flow patterns, e.g., by using coils in aneurysms; and
- Variation of the flow path, e.g., by using balloons to occlude a vessel.
Many of these effects can be simulated by adjusting the arterial tree
configurations. For instance, if one of the arteries is temporarily occluded by an
inflated balloon (Fig.
4
c), it can be computationally removed from the tree because
there is no flow in that artery. The flow variation can then be analyzed for the
remaining arteries.
