ManoUS: Samaneh CHOUPANI (CREATIS) defended her thesis on November 10th

Arterial stenosis refers to the narrowing or constriction of the arteries in the blood circulatory system, which obstructs normal blood flow. Such narrowing can lead to diminished blood flow, jeopardized oxygen supply, and potential complications like ischemia, tissue damage, or even complete blockage in severe cases. Timely diagnosis and appropriate treatment are crucial to manage arterial stenosis, prevent further complications, and maintain optimal blood flow.
Traditional approaches to assess arterial stenosis severity involve scanning the impaired region via vascular ultrasound, utilizing specific geometric criteria to grade severity. However, these geometric criteria, which are tied to the geometrical parameters of the stenosis, do not provide comprehensive information about its hemodynamic functionality, that could offer more detailed insights into stenotic blood flow. One potential solution involves measuring intravascular blood pressure loss between the inlet and outlet of a stenosis caused by post-stenotic turbulence and energy dissipation due to frictional forces within the fluid. Conventionally, this assessment is performed by catheterization, an invasive procedure with a risk of complications. As such, non-invasive blood flow imaging methods are often preferred to mitigate costs and potential side effects. Color Doppler ultrasound imaging is a non-invasive imaging modality that facilitates the study of intravascular flow. Its affordability and portability, combined with its ability to deliver real-time information about blood flow, make it an ideal choice for studying intravascular flow. However, it is essential to remember that the Doppler mode of echography provides a projection of blood velocity components along the ultrasound beam axis. By obtaining the velocity vector field and employing fluid dynamics equations, trans-stenotic pressure loss can be measured.
The study presented in this thesis aims to develop and examine the feasibility and applicability of a non-invasive technique utilizing clinical color Doppler imaging to estimate transstenotic pressure loss in mild to moderate cases of carotid artery stenosis. Such estimation will aid in assessing stenosis severity, allowing for earlier diagnosis. Our two-fold contribution to this study includes developing a vascular vector flow mapping technique (vVFM) for estimating the two-dimensional velocity vector field from the color Doppler scalar field by solving a constrained least squares problem using the Lagrange multipliers method. These constraints are related to fluid dynamics’ basic principles: mass conservation and free-slip boundary conditions. The second part of our contribution involves proposing a method for estimating trans-stenotic pressure losses based on fluid dynamics equations, where we suggest a combination of using the Bernoulli equation (upstream of the stenosis) and the Navier-Stokes equation (downstream of the stenosis). This non-invasive method was validated in silico via computational fluid dynamics and ultrasound simulations, and in vitro through particle image velocimetry and color Doppler ultrasound experiments on carotid stenosis models and phantoms in constant flows. This thesis demonstrates the reliability and feasibility of the proposed non-invasive method for trans-stenotic pressure loss estimation using clinical color Doppler.