Quantifying blood flow in the aorta using phase-contrast 4D flow MRI

Over the years, endovascular techniques have become the predominant treatment
option for most infrarenal aortic aneurysms, but more recently also for complex
aortic aneurysms such as juxtarenal abdominal aortic aneurysms (JAAA) and
suprarenal abdominal aortic aneurysms (SRAAA). Moreover, several endovascular
techniques were developed, which provide surgeons more treatment possibilities,
for instance, chimney endovascular aortic repair (ChEVAR), Branched
endovascular aortic repair (BEVAR) and Fenestrated endovascular aortic repair
(FEVAR). However, rigorous investigations should be performed to determine
their suitability and performance of various stent-grafts and configurations.
One of the most critical investigational aspects is the influence of the
stent-grafts on the blood flow trajectories inside and outside the treated
region. By quantifying the blood flow, we will be able to determine local
regions where flow complexity occurs, such as high shear, fluid stasis, and
flow recirculations. These regions of great importance since they might be
prone to unfavorable haemodynamics parameters, which could lead to (late)
complications. To date, in-vitro flow phantom studies and computational fluid
dynamics (CFD) simulations play essential roles in performing those studies,
owing to their ability to visualize and quantify the flow fields inside the
stent-grafts mimicking realistic properties of the in-vivo situation.

When performing such in vitro work, defining accurate and realistic flow
boundary conditions is crucial in order to get realistic outcomes. In short,
boundary conditions are defined as a set of constraints, such as pressure
(gradient) values, velocity fields in the geometry*s boundaries (i.e., inflow,
outflow and wall of arteries). In experimental studies, volumetric flow
profiles in various aortic cross-sections will define the boundary conditions,
with which blood flow can be determined in branched arteries throughout the
aorta. Unfortunately, well-structured data and descriptions for aortic flow
boundary conditions are not available in the literature. Therefore, researchers
had to rely on boundary settings mentioned, whether in old analytical papers or
obtained from animal studies.
In this study, we aim to perform phase-contrast (PC) 4D flow magnetic resonance
imaging (MRI) over a cohort of healthy volunteers to acquire adequate human
flow boundary conditions from the aortic arch to the internal/external iliac
arteries, including branched arteries (i.e., subclavian arteries, common
carotid artery, and visceral branch vessels). The obtained data will provide
profound knowledge regarding actual flow profiles in different aortic segments
of a healthy cohort, which is essential information to design more realistic
and reliable in-vitro and/or CFD studies in the future. Thus, after completing
the study and analyzing the data, the results will be published in a
peer-reviewed journal. Ultimately, this provides the research community with
insight into realistic blood flow boundary conditions.

Obtain phased-contrast 4D flow MRI scans in 20 healthy volunteers to quantify
local blood flow in the thoracic and abdominal aorta and extract boundary
conditions for future in vitro studies. Furthermore, the 3D geometry of the
vessels within investigated FOVs, starting from ascending aorta to
internal/external iliac arteries, will be obtained by performing a separate MRI
sequence.

An observational study will be performed in 20 healthy volunteers.

The included healthy volunteers have to visit the University of Twente for a
single day. The entire procedure will take about 1.5 hours and consists of
approximately 20 minutes of introduction followed by 50-60 minutes for
performing the MRI scans, and around 5-10 minutes closure at the end of the
study.
The present study carries no risks for the participant. The Siemens Magnetom
Aera is used in clinical practice and judged to be a safe diagnostic procedure.