Minimally invasive therapeutic techniques
A. Hepatic embolisation by glue injection
Glue embolization is a therapeutic treatment technique used to block
the blood flow to specific targeted sites by injecting surgical glues
that polymerize in contact
with blood. One application concerns patients suffering from malignant
liver tumors, who need to undergo partial liver ablation (figure 1).
When the volume of the remnant liver
part is not sufficient, preoperative portal vein embolization is used
to arrest blood flow in the liver part to be resected. This induces the
hypertrophy of the remnant
liver and enables the ablation procedure after a couple of weeks.
Figure 1: Glue is injected percutaneously to embolize the part of the liver to be resected.
From a fluid mechanics point of view, embolization is governed by the
dynamics of two co-flowing immiscible fluids, which is coupled with the
kinetics of glue
polymerization. Experimental investigations on drop formation in
liquid-liquid systems have shown the existence of two regimes, dripping
and jetting. Most studies have focused on dripping in unconfined
environment. We aim at characterizing the flow topology during portal
vein embolization by studying experimentally the confined
liquid-in-liquid injection, neglecting glue polymerization as a first
approach.
An experimental setup has been designed to create and visualize the
co-flow of two immiscible fluids. The dispersed phase is injected
through a capillary tube into the continuous phase, which flows steadily in a straight cylindrical tube.
The experiment is conducted in similarity with the physiological case.
We find that both regimes may occur during hepatic embolization (figure
2). Large drops form periodically during the dripping regime. During
jetting, a jet forms instead at the tip of the catheter and
destabilizes after a short distance, leading to the formation of small
drops. The dripping-to-jetting transition is governed by the ratio of
the inertial forces of the injected phase to the interfacial forces
with the external phase (Weber number).
During dripping, the drop size is only dependent upon the ratio of the
viscous forces of the external face to the interfacial forces
(capillary number). An analytical model has been develop to predict the
drop size evolution; good agreement is found with experimental data.
During jetting, the drop size tends towards a constand value, which is
a function of the jet diameter.
a.
b. 
Figure 2 : In vitro experiment simulating the injection of a non-miscible fluid in a co-flow. (a) Dripping regime. (b) Jetting regime.
Collaborators
Dr. Olivier Balédent, Service de Biophysique
et Traitement de l’Image, CHU Amiens
Dr. Roger Bouzerar, Service de Biophysique
et Traitement de l’Image, CHU Amiens
Prof. Marc-Etienne Meyer, Service de Biophysique
et Traitement de l’Image, CHU Amiens
Dr. Thierry Yzet, Département de Gastroentérologie,
CHU Amiens
Prof. Hervé Deramond, Département de Neuroradiologie,
CHU Amiens
Dominique
Haye, Plate Forme Mécatronique, Saint Quentin
Mihai-Cristinel Sandulache, Caractérisation in vitro de la technique endovasculaire d’embolisation par colle chirurgicale, PhD thesis, UTC, October 2011.
Bilal Merei, Etude de l’embolisation hépatique par colle. Simulation numérique de l’injection dans une veine hépatique, Master Thesis, UTC, September 2010.
Océane Lançon, Etude in vitro de l’injection d’une colle chirurgicale pour l’embolisation hépatique, Master Thesis, UTC, September 2012.
B. Stenting of arterio-venous fistula
An
arteriovenous fistula (AVF) is a surgical vessel connection between an
artery and a vein. It is created in end stage renal disease to provide
adequate blood access for hemodialysis. In the present study, the local
hemodynamics is investigated in a patient-specific AVF using a
computational fluid structure interaction (FSI) simulation. The fluid
and solid governing equations are solved using ANSYS (ANSYS, Inc.).
We focus on an end-to-side AVF between the end of the ce-phalic vein
and the brachial artery. The geometry of the vessel lumen is obtained
from CT-scan angiography. The vessel wall is modeled as a monolayer of
shell elements of uniform thick-ness, since the actual wall thickness
cannot be obtained from medical images.
We investigate the effect of the presence of a severe stenosis upstream
of the anastomosis by comparing two different geometries: model 1
consists of the complete patient-specific AVF, presenting a stenosis
inside the proximal brachial artery and an enlargement at the cephalic
vein; model 2 is obtained from model 1 by substituting the stenosed
artery with a straight cylinder.
For both models, a physiological time-dependent velocity in-let profile
and flow-dependent resistive pressure outlets are imposed as boundary
conditions. The hyperelastic, 3rd-order Yeoh model is used as
constitutive law to model the vessel wall.
The presence of the stenosis increases the mass flow through the vein by 9.6%. But
even if the flow rate increases slightly, the WSS in the cephalic vein
remains lower than the physiological range during the entire cardiac
cycle. The stenosed case is therefore more likely to suffer from the
formation of atherosclerotic plaques in this region. Stent placement in
the case of stenosed AVFs would be beneficial as it would greatly
reduce the vein area subjected to pathological flow conditions.
a. 
b. 
Figure 3: (a) Forearm anatomy in a patient with an arterio-venous fistula. (b) Patient-specific geometry used in the fluid-structure interaction numerical simulation.
Collaborators
Dr. Zaher Kharboutly, BMBI, UTC
Dr. Cécile
Legallais, BMBI, UTC
Dr. Vanessa Diaz, University College London (UK)
Prof. Gabriele Dubini, Politecnico di Milano (Italy)
Dr. Justin Penrose, ANSYS UK (UK)
Iolanda Decorato (PhD student), Simulation
numérique des interactions fluides structure dans une fistule
artério-veineuse : effet de la pose d’un stent sur l’hémodynamique, UTC.
Tommaso Vassallo, Etude in vitro de l’hémodynamique dans une fistule artério-veineuse, Master Thesis, UTC, September 2012.