PULSE - UCSD Jacobs School of Engineering Newsletter

Diagnostic Technology to Improve Management of Deadly Aneurisms
UCSD engineers and physicians are developing software to assess the risk of abdominal aortic aneurism rupture.

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.

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.

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
intervention.

“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 manufacturing techniques.

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.