Diagnostic Technology to Improve Management
of Deadly Aneurisms
UCSD engineers and physicians are developing software to assess the
risk of abdominal aortic aneurism rupture.
UCSD researchers are seeking to better monitor the progression
of the disease process in abdominal aortic aneurysms by quantifying mechanical
stresses acting on the vessel walls. An abdominal aortic aneurysm (AAA)
is a dilation of the aorta (similar to a balloon) that poses a risk to health
due to the potential of rupture, clotting, or dissecting. Nearly two million
patients suffer from AAA in the United States and 250,000 new cases are
detected each year. Rupture of aneurysm and complications related to surgery
make AAA the 13th leading cause of death in the U.S.
Juan Lasheras and Steven Sparks display their model
of an abdominal aorta with an insipient aneurism. The model was manufactured
by Mike Bailey at the San Diego Supercomputer Center.
The study, co-directed by Prof. Juan C. Lasheras of the Jacobs School
and Prof. Steven R. Sparks, M.D., of the School of Medicine, aims at developing
a quantitative assessment of the risk of aneurysm rupture, and at providing
an improved guideline for surgical or endovascular
“The proper assessment of the risk of rupture is something we are
currently missing,” says Sparks, UCSD Chief of Vascular Surgery.
“Although it is widely recognized that increasing size leads to
a higher risk of rupture, small aneurysms can rupture and others can enlarge
without rupture. This leaves physicians to face the therapeutic dilemma
of either subjecting patients with small AAAs to a complex surgery or
to an increasing risk of aneurysmal rupture.”
Lasheras’ and Sparks’ innovative method consists
of using high resolution computerized tomography (CT) scans and magnetic
resonance imaging (MRI) to reconstruct a three-dimensional model of the
arterial tree including the AAA. The researchers have developed a finite-element
computer code incorporating non-linear elastic effects and all physiological
and mechanical information of the arterial wall, including the possible
presence of a blood clot. The code computes the distribution of stresses
along the aneurysm’s wall to provide information on the possible location
of rupturing and a quantification of the risk of rupture.
The expected outcome of this study is the development of software which
could be incorporated into radiological imaging devices to compute the
wall stress patterns at each stage during the cardiac cycle. This dynamic
calculation would be based on measurements of the patient's blood pressure
and blood flow rate to the aorta, and imaging information about the shape,
thickness and composition of the vessel’s and aneurysm’s walls
as well as the mechanical properties of the wall tissue itself.
“Despite the large body of evidence that implicates inflammatory,
degenerative and complex pathophysiology in the wall of the aneurysm in
the etiology of AAAs, none of these factors has proven useful for predicting
the most lethal consequence of AAAs--sudden rupture,” says Lasheras.
“Regardless of the process whereby the arterial wall composition
and strength change, it is beyond any doubt that the onset of rupture
is due to the failure of the wall structure to support the stresses resulting
from the pulsatile blood flow. That is the information vascular doctors
need the most to determine when to intervene.”
The project involves interdisciplinary, collaborative research of physicians
specializing in radiology and vascular medicine, as well as engineers
and computer scientists specializing in fluid mechanics, computational
mechanics, mechanical behavior of elastic membranes, laser-based diagnostics
of turbulent flows, computer-aided visualizations and rapid prototyping
Project Director Lasheras is a professor and chairman of the Department
of Mechanical and Aerospace Engineering, and a member of the Whitaker
Institute of Biomedical Engineering. Project co-Director Sparks is an
associate clinical professor of surgery at the UCSD School of Medicine
and holds a joint appointment at the Jacobs School. The team also includes
Jacobs School professors Michael Bailey and David Benson, and UCSD School
of Medicine radiologists William Bradley (professor and chair of the Department
of Radiology) and Thomas Kinney. Mechanical and aerospace engineering
graduate research assistants Anne-Virginie Salsac and Maria-de-Gador Canton
are also participating.
Lasheras is no stranger to the development of technologies for medicine.
INNERCOOL, the San Diego medical device company co-founded by Dr. John
Dobak and Professor Lasheras, has already received FDA approval to market
its Celsius Control™ System, a novel endovascular cooling technology.