Vector Flow Imaging in healthy vessels

There is a wealth of evidence implicating the important role of blood flow
throughout all stages of the process of atherogenesis. Two locations along the
vascular tree at which atherosclerotic plaques are typically found are the
carotid artery (CA) and the superficial femoral artery (SFA). Nowadays,
ultrasound is the technique of choice for assessing the vascular condition in
the CA and SFA. However, clinically used ultrasound techniques show a large
variability in estimating the blood flow velocity, due to multiple limitations.
With the advent of ultrafast ultrasound imaging, (almost) all elements of the
transducer can be activated simultaneously. These so-called plane wave
acquisition acquires thousands of images per second and makes continuous
tracking of blood flow velocities in all directions in the field of view
possible. This high-frame-rate acquisition opened up new possibilities for
blood flow imaging at the CA and SFA, such as blood Speckle Tracking (bST) and
ultrasound Particle Image Velocimetry (echoPIV). Both these vector flow
imaging (VFI) techniques enable the quantification of 2D blood flow velocity
profiles, where bST uses no contrast agents compared to echoPIV. Beside these
novel ultrasound based techniques, 4D Phase Contrast Magnetic Resonance Imaging
(4D flow MRI) enables a non-invasive quantification of the 4D blood flow
velocity profiles (3D + time) and can be used as reference standard for blood
flow assessments in-vivo. We therefore aim to evaluate the performance of both
VFI techniques in comparison to 4D flow MRI measurements in the CA and SFA of
healthy volunteers.

Primary objective:
To evaluate the performance of bST and echoPIV in quantifying spatiotemporal
blood flow velocity profiles in the CA and SFA of healthy volunteers in
comparison to 4D flow MRI.

Secondary objective:
- To determine the correlation of spatiotemporal blood flow velocity profiles
obtained with bST and echoPIV;
- To compute flow-derived parameters, such as vector complexity, vorticity and
WSS, from the spatiotemporal blood flow velocity profiles and determine the
correlation between all three techniques (bST, echoPIV and 4D flow MRI);
- To compare spatiotemporal blood flow profiles and flow-derived parameters
between young and old healthy volunteers;
- To determine the intra- and inter-observer variability (i.e. repeatability
and reproducibility, respectively) of bST in the CA.

Prospective, observational, feasibility study in a total of twenty healthy
volunteers.

The burden for volunteers related to this study consists of a visit to the
hospital. During this visit the bST, echoPIV, and 4D flow MRI measurements will
be performed. The bST and echoPIV measurements will be performed using a
research ultrasound machine that is not approved for clinical use. All required
tests were performed to ensure a safe use of the machine. Moreover, ultrasound
contrast agents will be intravenously injected that have a small risk of
adverse events (<0.01%). At last, 4D flow MRI scans will be performed, which
might be unpleasant because of the small tube and loud noise.