Engineering Approach to Blood Flow Aims to Improve Stroke Treatment

BUFFALO, N.Y. -- As a mechanical engineer, Hui Meng built her career on the study of turbulent flows generated by jet engines, aerosol particles and other aerodynamic systems. Today she's turned her focus to biomedical engineering and is applying her skills to understanding flow in the tiny blood vessels that lead to the human brain.

A professor of mechanical and aerospace engineering in the University at Buffalo's School of Engineering and Applied Sciences and research professor of neurosurgery in the UB School of Medicine and Biomedical Sciences, Meng is a member of a select, but growing, cadre of engineers whose quantitative skills are sought after increasingly by the clinicians who treat patients with brain aneurysms.

At UB's Toshiba Stroke Research Center, where she is a co-director, Meng leads a research team that studies the relationship between blood flow and brain aneurysms, abnormal pouching of brain vessels that can lead to the most severe form of stroke -- hemorrhage -- when they rupture.

Meng is funded by an $800,000 "K25" Career Award from the National Institutes of Health, specifically designed to transfer quantitative skills developed for the physical sciences and engineering to the life sciences for the ultimate benefit of human health. The grant allows Meng to direct her career focus to biomedical research.

In a nation where the aging population is growing and stroke is the third-leading cause of death, the study of blood-flow dynamics and other risk factors that cause stroke is of primary concern for neurosurgeons.

"Interventional neurosurgeons and neuroradiologists are in desperate need of quantitative treatment guidance and fundamental understanding of vascular abnormalities," said L. Nelson Hopkins, M.D., director of the Toshiba Stroke Research Center in UB's School of Medicine and Biomedical Sciences, under whom Meng conducts her research.

Within three to five years, Meng and her UB colleagues plan to develop a complete platform for virtual intervention in which computer models will demonstrate to clinicians how the insertion of stents, coils and other devices through catheters into the brain's blood vessels will affect each patient's blood flow, and therefore the clinical outcome.

A virtual intervention platform would allow clinicians to develop tailored treatment by "experimenting" with various treatment options through computer simulation.

During the past decade, UB's Toshiba Stroke Research Center has pioneered some of the most successful minimally invasive surgical techniques, and it continues to lead in developing new treatments today.

Along with the advent of these new endovascular treatments has come recognition that a more sophisticated understanding of hemodynamics (blood-flow dynamics) and its effect on vascular biology is necessary since these minimally invasive treatments themselves directly alter a patient's hemodynamics.

"It's not always intuitive how mechanical forces interact with biology," Meng said.

"We know that blood-flow dynamics play a critical role in the initiation, growth and rupture of an aneurysm, but we don't know through what cellular and molecular mechanisms. Local changes in blood flow alter the gene expressions of the abnormal vessels, thereby offering opportunities for therapy.

"Since each patient's vessel anatomy is different, each case has to be computed individually to get the accurate flow dynamics," she continued.

Meng and her colleagues rely on medical imaging, such as MRI, CT or rotational angiography, to provide the patient's three-dimensional vessel anatomy around an aneurysm.

"Based on the patient's blood flow and our understanding of how blood flow interacts with vessel biology, we try to predict the risk of an existing aneurysm rupturing," she said.

"We look at the flow data, and we say 'Here's where the highest shear stress and pressure are and therefore this is likely or not likely to continue to grow and rupture.' We suggest to the clinician how the flow should be modified to reduce the rupture risk," she said.

Meng and her UB colleagues currently are simulating patient hemodynamics using techniques borrowed from mechanical engineering, such as computational fluid dynamics, a technique originally developed to simulate flows in engines and around automobiles, and particle image velocimetry, which provides measurements of flow fields.

The goal is to assess the effectiveness of hemodynamic intervention, methods of improving the outcomes of stroke patients by redirecting blood flow.

"If you change the flow in a blood vessel, the vessel responds by remodeling," said Meng.

Aneurysms, particularly large ones, can rupture, causing hemorrhage inside the skull, but since aneurysms are usually asymptomatic, Meng noted, it's difficult to know which should be treated and which can be left alone.

What further complicates treatment is the fact that the geometry of blood vessels, aneurysms and arteries varies from patient to patient; at the same time, aneurysms and treatments for them, such as stenting, alter blood flow.

Such factors influence the types of aneurysms that occur, how they grow, whether or not they will rupture and reoccur, how they heal after surgery and which interventions will prove most successful in each case.

Meng and her colleagues have begun establishing a patient-specific computational fluid-dynamics modeling platform and designing experimental models that mimic blood-flow patterns through and around blood-vessel abnormalities.

Right now, the team performs "virtual interventions" on animal models and on a few human patients' aneurysm CT images.

"The goal is to be able to provide the surgeons with the individual-based feedback they want to guide them in making the best treatment decisions," said Meng.

In addition to Meng, the research team in UB's Toshiba Stroke Research Center working on the project includes Scott H. Woodward, deputy director of the hemodynamic laboratory, John Kolega, Ph.D., associate professor in the UB Department of Pathology and Cell Biology, Daniel Swartz, Ph.D., research assistant professor in the UB Department of Pediatrics and Dale Taulbee, Ph.D., professor in the UB Department of Mechanical and Aerospace Engineering.

The team also includes the center's medical imaging physicists Steven Rudin, Ph.D., UB professor of radiology and research professor of biophysical sciences and neurosurgery; Kenneth Hoffman, Ph.D., associate professor of neurosurgery, and Lee Guterman, Ph.D., M.D., and Elad Levy, M.D., both associate professors of neurosurgery and radiology, as well as center neurosurgeons and fellows.

The University at Buffalo is a premier research-intensive public university, the largest and most comprehensive campus in the State University of New York.