Imaging Innovation: 4D Flow MRI and Carotid Webs

Award-Winning Research

Biomedical engineer Retta El Sayed has pioneered a way to use advanced imaging to see and quantify the effects of a specific vascular anomaly on blood flow, which in turn could help doctors identify patients at risk of having what previously was thought to be strokes of unknown cause (known in medicine as cryptogenic strokes).

smiling person with long dark hair wearing a colorful top

Carotid webs are a rare anomaly in the vasculature of the carotid artery. Because these fibromuscular structures project into the internal carotid artery, they are suspected of impairing blood flow and could be linked to up to one-third of cryptogenic strokes. The anomaly predominantly affects younger women of African American descent, a group underserved by current cardiovascular health care providers.

graphic showing how blood flows in the carotid artery and compares normal artery with one with web and one with atherosclerosis

El Sayed devoted her doctoral program in biomedical engineering to assessing complex blood flow patterns in patients with carotid web. “From the outset, my objective was to conduct a comprehensive study comparing patients with carotid web to those with atherosclerosis and normal volunteers to assess the link between carotid web and stroke risk.”

She quickly homed in on 4D flow magnetic resonance imaging (MRI) because it non-invasively measures blood flow patterns in arteries. Sounds easy, but the high-tech scanner doesn’t come with pre-set sequences for imaging and assessing blood flow in small arteries like the carotid.

“Because there were no existing scanning parameters, we first had to estimate our scan parameters and then validate them through a phantom study to ensure the accuracy and reliability of our data collection methods,” El Sayed explains.

The team used two different measures of blood flow linked to vascular dysfuntion and thrombosis, or the forming of clots. Time-averaged wall shear stress measures the force of exerted by the wall of the artery on blood flow and oscillatory shear index measures blood flow recirculation. Higher values are associated with normal blood flow. The lower the shear stress and oscillatory shear, the greater the opportunity for atherosclerotic plaque to build on arterial walls and also the riper the conditions for forming blood clots.

(Left: streamlines of blood flow through a normal carotid artery.)

The team found 4D flow MRI did, indeed, measure blood flow disturbances from carotid webs that put patients at higher risk of stroke than even patients with atherosclerotic plaque, which is a major contributor of stroke. The findings also validated the 4D flow MRI scanning parameters and technique, results with profound implications for addressing a deadly disparity in cardiovascular health care.

(Right: graphic showing how blood flow is impaired in the presence of a carotid web and as a result of atherosclerosis.)

colorful images of blood flow velocity and other factors taken by 4D flow MRI

El Sayed already is planning ways to build upon the results of this study to further develop diagnostic tools aimed at enhancing clinical decision-making. “My goal is to advance the field by refining methods that can better predict and manage patient outcomes.”

Emory: A Leader in Imaging Innovation

Emory is exactly the right place to do this work. Helming Emory’s Center for Systems Imaging, which is a leader in 4D flow MRI research, is John D. Oshinski, professor of radiology and imaging sciences and biomedical engineering and a leader in using MRI to study vascular hemodynamics. Oshinski is El Sayed’s mentor and co-advisor, along with Jason Allen, a neuroradiologist and expert in cryptogenic strokes, specifically carotid web. Allen directed Emory’s Division of Neuroradiology before becoming chair of the Department of Radiology and Imaging Sciences at Indiana University School of Medicine in late 2023.

Emory also has faculty teams in the Department of Neurology dedicated to treating patients with carotid web, a rare but potentially devastating condition. Both Diogo Haussen, associate professor of neurology, neurosurgery and radiology, and Fadi Nahab, assistant professor of neurology and pediatrics, recruited enough patients from their practice to ensure results would be statistically significant.

El Sayed’s work is so groundbreaking, it graces the cover of the June 2024 issue of the Journal of Magnetic Resonance Imaging. It also scored her the W.S. Moore Young Investigator Award from the International Society of Magnetic Resonance in Medicine. It naturally secured her doctoral degree in biomedical engineering, which the Coulter Department of Biomedical Engineering at Emory and Georgia Tech conferred in May.

cover of the Journal of Magnetic Resonance Imaging June 2024 with colorful images of arteries taken using 4D flow MRI