CMR-Flow

1337035 - Assessment of Complex Flow Patterns in Patients with Carotid Webs, Patients with Carotid Atherosclerosis, and Healthy Subjects using 4D Flow MRI

Friday, January 27, 2023

10:20 AM – 11:00 AM

Location: Pacific Jewel

Presenting Author(s)

RE

Retta El Sayed, MSc

Ph.D. candidate
Emory University
Atlanta, Georgia, United States

Primary Author(s)

RE

Retta El Sayed, MSc

Ph.D. candidate
Emory University
Atlanta, Georgia, United States

Co-Author(s)

CP

Charlie C. Park, MD

Radiology Resident
Emory University, United States
FN

Fadi B. Nahab, MD

Associate Professor
Emory University, United States
DH

Diogo C. Haussen, MD

Associate Professor
Emory University, United States
JA

Jason W. Allen, MD, PhD

Associate Professor
Emory University, United States
JO

John N. Oshinski, PhD

Professor of Radiology and Biomedical Engineering
Emory University
Atlanta, Georgia, United States

Background: Carotid webs (CaWs) are intraluminal shelf-like projections in the ICA bulb that cause mild narrowing of < 50%.¹ CaWs are linked to strokes and may account for one-third of cryptogenic strokes in younger patients (< 50) without vascular risk factors.¹ CaWs are not associated with inflammation or plaque deposition but cause significant hemodynamic disturbance including blood recirculation and stagnation.² Understanding the CaW-associated hemodynamic alterations is imperative to assessing stroke risk. Wall Shear Stress (WSS) and Oscillatory Shear Index (OSI) are two parameters that have been linked to vascular dysfunction and thrombus formation.³ In this study, we used 4D flow MR to characterize carotid hemodynamics in three groups: 1) subjects with CaWs, 2) subjects with atherosclerosis (with a similar degree of stenosis), and 3) healthy subjects. The aim is to quantify time-averaged WSS (TAWSS) and OSI in these groups with the long-term goal of improving our understanding of clot formation and stroke in patients with CaW. Hypothesis: CaWs are associated with lower TAWSS and higher OSI than mild atherosclerosis or healthy carotids.

Methods: IRB-approved study (n=15). Patients with CaWs (n=5, 5F, age 46±10) and a history of stroke or TIA with mild luminal narrowing (39±12%), subjects with mild atherosclerosis (n=5, 2F, age 71± 11, % stenosis 44±6%), and healthy volunteers (n=5, 5F, age 46±16) were included. All subjects were imaged on a 3T system (MAGNETOM Prismafit, Siemens Medical Solutions). 4D flow MRI images were acquired for each carotid (FOV=162*200mm², 1mm³;flip-angle=7°; TR=45ms; TE=5ms). Processing was performed using a custom-written MATLAB code to correct for eddy currents and aliasing, perform noise filtering and create a 3D magnetic resonance angiogram (MRA).^3,4 MRA images were segmented using Mimics and imported into EnSight (ANSYS Inc, 2019) for streamline visualization. Four planes were placed perpendicular to the centerline: CCA plane at 1 diameter (D) below the carotid bifurcation, and ICA planes at 0.5D, 1D, and 1.5D downstream from the maximum stenosis⁵, Figure 1. TAWSS and OSI were quantified using MatLab allowing manual lumen contours as vessel walls for all time frames.⁴

Results: TAWSS was lower in CaW cases (0.3±0.1N/m²) than atherosclerosis (0.6±0.3N/m²) or normal subjects (0.4±0.1N/m²) and differences were statistically significant (p< 0.05). For OSI, the plane in the CCA and ICA 1.5D showed no differences between the groups. OSI at the ICA plane 0.5D and 1.0D was significantly higher in CaW cases than in atherosclerosis (p< 0.05), Figure 2. Results show that in the region distal to the web (0.5D-1.0D downstream), CaW induced significant complex hemodynamics (higher OSI) compared to atherosclerotic lesions with a similar degree of luminal narrowing.

Conclusion: Lower WSS and higher OSI are present in patients with CaW when compared to patients with atherosclerotic lesions or healthy subjects, and these factors may predispose the region to clot formation.