Feasibility of the use of Ultrasound Doppler-derived patient-specific velocity profiles in fluid-structure interaction modelling of the abdominal aorta, femoral artery and carotid artery

Cardiovascular diseases are the number one cause of death worldwide. Early
diagnosis and treatment are therefore very important. There are two different
types of vascular diseases: aneurysmal vascular disease (dilatation) and
stenotic vascular disease (narrowing). An aneurysm can develop in different
types of blood vessels, but most often occurs in the abdominal aorta. Rupture
of an abdominal aortic aneurysm (AAA) is a major cause of death in the Western
world, given the high mortality rate in case of rupture (80%). To prevent
rupture, AAA patients visit the hospital every 3-12 months for a checkup,
during which the diameter of the aneurysm is measured. Since AAA surgery is not
without any risks, surgery is performed only when the rupture risk is greater
than the surgery risk: the risk of complications during and after surgery.
Currently, the rupture risk is based on the maximum diameter and growth rate of
the aneurysm. Surgery is performed when the maximum diameter is greater than
5.5 cm or the diameter has increased more than 1 cm in one year. However, this
criterion is not optimal, as there are cases where small aneurysms with a
diameter of 3 cm have been ruptured and large aneurysms with a diameter of 7 cm
that are still stable. Therefore, there is need for another method to be able
to estimate the rupture risk better. With fluid-structure interaction (FSI)
models we can model the blood flow through the aneurysm, from which we can
derive for example the stress on the wall and the shear stress at the wall.
These models already use a patient-specific geometry as measured with 3D
Ultrasound. Research towards the hemodynamics in AAA's has shown that rupture
occurs in areas of low wall shear stress. However, this is in contradiction
with studies on the wall mechanics of AAA's, in which is shown that regions
with a high wall stress are prone to rupture. Therefore, it can be concluded
that the hemodynamics and wall mechanics do not provide enough information
separately. In FSI simulations, the hemodynamics and wall mechanics are
combined and these models could therefore help to improve the estimation of the
rupture risk. Aneurysms can also occur in smaller blood vessels such as the
femoral artery and carotid artery. However, a stenosis is more often found in
these smaller blood vessels, which is caused by plaque formation
(atherosclerosis). Research has shown that areas with a low wall shear stress
are more prone to plaque formation. Therefore, the FSI models can also be used
to estimate the stenosis progression and thus determine whether surgery is
needed or not. Currently, a generic velocity profile over time and over the
diameter of the blood vessel is used in these models. To further improve the
estimation of the rupture risk and stenosis progression, this general velocity
profile could be replaced by a patient-specific velocity profile. With Pulsed
Wave and Color Doppler ultrasound, it is possible to measure the velocity of
blood to obtain an inlet velocity profile over the cross section (Color
Doppler) and over time (Pulsed Wave Doppler). However, a drawback of Ultrasound
is that it is sensitive to noise and only the velocity in the direction of the
probe can be measured (angle dependent). As a result, it is not possible to
distinguish the velocity in the axial direction (longitudinal direction of the
blood vessel) from possible vortexes, which could interfere with the velocity
measurement. With 4D Flow Magnetic Resonance Imaging (MRI), it is possible to
measure the x- y- and z-components of the velocity in the blood vessel, which
can be used to compare the velocity profile measured with Doppler Ultrasound
with the MRI derived velocity profile. Because of the low resolution of 4D flow
MRI, it is only applicable in larger blood vessels such as the aorta.
Therefore, for the smaller blood vessels 2D PCMRI will be used to compare the
US-derived velocity profile. MRI is less sensitive to noise and this velocity
profile can therefore be considered as the gold standard.

Main goal:
The main goal of the study is to show the feasibility of using Doppler US
derived patient specific velocity profile in the abdominal aorta, carotid
artery and femoral artery, in order to improve the Fluid-Structure-Interaction
models of AAAs, carotid artery stenoses and femoral artery stenoses. The
velocity profiles will be compared to 4D flow MRI (abdominal aorta) or 2D PCMRI
(femoral and carotid artery) derived velocity profiles.

Secundary goal:
The 4D Flow MRI can additionally be used to validate the FSI model. With 4D
Flow MRI it is possible to reconstruct the streamlines of flow through the
aneurysm, which can then be compared to the streamlines of flow through the
aneurysm in the FSI simulations. In addition, from the measured velocity, the
wall shear stress (WSS) and the oscillatory shear index (OSI) can also be
determined with which the WSS and OSI calculated with the FSI simulation can be
validated. Also the wall displacements can be derived from the MRI data, which
can be compared to the simulated wall displacements with the FSI simulations.
Lastly, the 4D flow MRI data will be used to validate the stiffness estimation
of the aortic wall.

This is a study with AAA patients and patients with an asymptomatic stenosis of
the carotid or femoral artery, who are under surveillance at the Catharina
Hospital. In addition, 24 healthy subjects will also participate in the study.
When the patient/volunteer agrees to participate in the study, a Pulsed Wave
and Color Doppler ultrasound scan of the abdominal aorta, femoral artery or
carotid artery will be performed. In addition, a 4D flow MRI (aorta) or 2D
PCMRI (femoral and carotid artery) scan will be performed. Both scans do not
use harmful radiation and therefore pose no risk to the patient/volunteer. In
total, the examination will take approximately one hour. To minimize the time
burden on the patient, an attempt will be made to schedule the additional
ultrasound and MRI examination right after the check-up.

Offline analysis will be performed on the Ultrasound and MRI data sets.
Post-processing will be performed by the principal investigator, at and in
collaboration with the Eindhoven University of Technology (TU/e).

Participation in this study provides no personal benefits to the patients and
volunteers. The study will cost the patient approximately one hour of extra
time. Non-harmful imaging modalities (Ultrasound and MRI) will be used during
the study. The study is therefore without any risks. Only when a subject has
metal implants, the MRI could cause damage. Therefore, the patients will be
screened for metal implants in advance and those patients with a metal implant
will be excluded from the study. Also for patients with claustrophobia, the MRI
can be experienced as a burden. These subjects will therefore also not be
included in the study.