Feasibility of ultrasound particle image velocimetry to quantify flow in the abdominal aorta before and after endovascular aneurysm repair

An abdominal aortic aneurysm (AAA) is a common vascular disease with a high
mortality in case of rupture. The underlying processes initiating aneurysmal
degeneration and driving aneurysmal growth remain poorly understood. Local
hemodynamics might play a key role in the pathogenesis of AAA, as it is
associated with aneurysmal growth, intraluminal thrombus formation and rupture
risk. Visualizing and quantifying local blood flow profiles could eventually
provide more insight in the underlying mechanisms of aneurysm progression as
well as identify smaller AAA with increased vulnerability or larger AAA with
low risk of rupture. Consequently, this may improve risk assessment and provide
patient-specific therapy guidance. Nowadays, endovascular aneurysm repair
(EVAR) is the preferred treatment modality in most patients with an infrarenal
AAA. However, EVAR is associated with a relatively high reintervention rate. It
is hypothesized that the placement of a stent graft may alter local
hemodynamics and subsequent recirculations or flow stagnations promote the
onset of thrombosis or micro-emboli. These unfavourable flow conditions might
be related to various complications after EVAR, such as limb occlusion (6.5%
within 6 months), renal dysfunction (3.3%), and the persistence of type II
endoleaks (10.2% with type II endoleaks of which only 35.4% resolved
spontaneously). Visualizing local blood flow profiles after EVAR might provide
insight in these (un)favourable conditions.
In vivo blood flow quantification is a great challenge, particularly in the
abdomen. Advanced ultrasound based techniques, incorporating ultrasound
contrast agents and plane wave imaging, proved to be feasible in quantifying
aortoiliac blood flow patterns in healthy volunteers.

The aim of this study is to determine the feasibility of ultrafast
contrast-enhanced ultrasound particle image velocimetry (echoPIV) measurements
to quantify spatiotemporal blood flow velocity profiles in the abdominal aorta
of AAA patients before and after endovascular repair.
Secondary objectives are to determine the correlation between echoPIV and
phase-contrast MRI (PC MRI) based measurements to ultimately validate the
spatiotemporal velocity profiles obtained with echoPIV. Furthermore, changes in
blood flow velocity profiles after placement of a stent graft will be
evaluated.

Feasibility study.

The burden for subjects related to this study consists of 1 extra visit to the
hospital prior to their scheduled endovascular treatment. During this visit the
preoperative echoPIV and PC MRI measurements will take place. The postoperative
echoPIV measurements and PC MRI scan will not require an additional visit,
since this will be scheduled on the same day as the clinical follow-up visit.
The echoPIV measurements will be performed using a research ultrasound machine
that is not approved for clinical use. The required tests were performed to
ensure a safe use with the subjects. Moreover, during the echoPIV measurements
an ultrasound contrast agent will be intravenously injected. With the use of
these contrast agents there is a small risk of adverse events. To this end,
appropriate safety measures have been realized at our vascular centre where the
measurements will take place. Also, two PC MRI scans will be performed which is
not part of standard care.