(Editor’s Note: May is National Stroke Awareness
Month)
PHYSICIANS AND ENGINEERS POOL RESOURCES TO
PREVENT STROKE
Methodist Neurological Institute Doctors Work
with UH Engineers on New Tool to Improve Brain Aneurysm Treatment
HOUSTON, May 8, 2006 – A professor at the University
of Houston and his research students are working with physicians
and scientists at the Methodist Neurological Institute (NI) on new
technology to help identify which brain aneurysms are at highest
risk of rupture and could cause a stroke.
Improving treatment of cerebral aneurysms, which are ballooning
weak spots in the wall of a blood vessel in the brain, is at the
center of this joint research. The goal of their study is to develop
a fully-integrated computational medical tool that will be useful
in helping to select patients for treatment whose aneurysms are
most likely to rupture.
Ralph Metcalfe, a mechanical engineering professor at UH and deputy
director of the UH biomedical engineering program and his graduate
student, Aishwarya Mantha, work on this project with a Methodist
team consisting of Drs. Charles Strother and Goetz Benndorf, interventional
neuroradiologists, and Christof Karmonik, a researcher at the Methodist
Hospital Research Institute.
Using computer simulations of blood flow in realistic geometric
models of aneurysms, some blood flow characteristics have been identified
that may contribute to aneurysm formation. These findings are described
in a paper titled “Hemodynamics in a Cerebral Artery Before
and After the Formation of an Aneurysm,” appearing in the
May issue of the American Journal of Neuroradiology, a scientific
journal that publishes original articles dealing with the clinical
imaging, endovascular therapy and basic science of the central and
peripheral nervous system.
“According to the American Association of Neurological Surgeons,
cerebral aneurysms affect up to six percent of the U.S. adult population,”
Metcalfe said. “Most aneurysms don’t rupture, but if
they do, the results are fatal in about 50 percent of the cases.
The question is how to predict who is most at risk.”
Since treatment of aneurysms is associated with some risk, Metcalfe’s
group and his Methodist colleagues are trying to develop a better
method of identifying which aneurysms are most vulnerable for rupture.
Once these patients are identified, physicians can then determine
the best course of medical treatment, using existing technologies
and best medical practices.
“One of the key points is that aneurysms don’t seem
to form randomly,” Metcalfe said. “They do seem to form
at locations that are associated with the fluctuations in the flow
of blood, leading to the question of what it is about the flow of
blood that tends to correlate with the formation of aneurysms.”
The Methodist researchers acquire 3-D images of the intracranial
vascular system by injecting dye into the vessels and rotating an
X-ray tube around the patient’s head, a technique that has
become a standard for high-quality vascular imaging in this institution.
By using this geometric and blood flow data taken from a specific
patient’s clinical profile, Metcalfe’s team can perform
simulations in their computers of blood flow in that patient’s
arteries using existing computational fluid dynamics programs in
novel applications. This is similar to the way that an aeronautical
engineer would study the design of an airplane on a computer or
in a wind tunnel. Strother and his colleagues at Methodist anticipate
that this process will help researchers better understand how aneurysms
form and ultimately discover ways to prevent strokes and death from
this common disorder.
“We can’t look at a person and tell the likelihood
that an aneurysm will rupture,” Strother said. “But
we do know that force and stresses created by blood flow produces
aneurysms. Our hope is that this study will help us learn enough
to predict which ones are at high risk of rupture so that treatment
can be offered before they become harmful.”
This work has two potential applications. The first is as a research
tool, with Metcalfe’s team performing simulations of specific
aneurysms. Using a technique employed by Karmonik to simulate removal
of an aneurysm on the computer, they analyze how the blood behaves
as it flows near the aneurysm site and determine if that can be
correlated to a certain type of behavior of the blood at potential
sites where aneurysms form. Very accurate simulations are done for
a complete description of the flow fields, studying all the fluid
dynamic variables in great detail, such as the wall shear stresses,
the pressures and the velocity.
“The second application is as a potential clinical tool,”
Metcalfe said. “Once we have a reasonable idea of the fluid
dynamic variables needed to study and identify a potential problem,
we then use a program that provides a detailed, 3-D description
of the aneurysms of the real patients.”
Benndorf adds that the potential clinical importance of these computer
simulations lies in the future possibility of directly predicting
patient-specific blood flow so that patient-specific medical devices
can be used in aneurysm treatment. He is studying how stents –
small wire mesh tubes that are inserted into the artery to facilitate
the occlusion of an aneurysm with small platinum coils – can
be tailored to the patient’s individual anatomy and blood
flow in order to optimize their therapeutic effect and maximize
the possibility of a successful outcome.
When Metcalfe’s group imports a patient’s images into
a computer program, they remove some geometric glitches and generate
a computational mesh that involves the mapping of hundreds of thousands
of tiny elements that represent the area being studied. That mesh
is then introduced into a program that actually solves the fluid
dynamic equations of motion.
“It takes a lot of computer time to perform these simulations,”
Metcalfe said. “There are several hundred thousand elements
that are discrete zones within a geometric mesh, and then there
are 700 steps representing intervals of time over the cycle of each
heart beat.”
Requiring extremely fast computers, the group uses the Beowolf cluster
at UH’s Texas Learning and Computation Center (TLC2) to significantly
improve the visualizations created by the simulations.
“The critical step here is to make these complicated flows
much more accessible to people like medical researchers and physicians,”
Metcalfe said. “We’re developing 3-D visualizations
so doctors can go inside the virtual artery and actually see what’s
happening as the blood cells flow through.”
Halliburton Company supports this joint project by funding the
research analysis of the study’s findings, which have the
potential for substantial impact in neurology and medical science.
For more information about The Methodist Hospital, call (713) 790-3333
or visit www.methodisthealth.com.
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