Using light to measure the dangers of aortic aneurysms will assist surgeons to decide when they should operate on a patient, writes Anna Nolan
Scientists at the University of Limerick have developed a sophisticated system for modelling abdominal aortic aneurysms (AAA), a method now being used in a US National Institutes of Health (NIH) project on the behaviour of aortic aneurysms. As well as contributing to the understanding of aneurysms, the model can help surgeons to decide whether to operate.
An AAA is a ballooning of the wall of the main artery of the body where it runs though the abdominal region. This excessive localised swelling occurs when the wall of the artery becomes diseased or weakened. If the aorta actually bursts, it can lead to very substantial bleeding.
When the problem is caught in time, fatality is low, but if left untreated the death rate is high.
It is estimated that every year about one in 250 people over 50 years of age dies from an AAA. In Ireland there are about 600 cases diagnosed annually.
While the medical challenges are clear, there remains considerable debate about the timing of surgical intervention, according to the director of the Centre for Applied Biomedical Engineering Research (Caber) at UL Tim McGloughlin.
There is agreement that an operation is generally needed where the maximum diameter of the balloon in the wall is more than 50mm (about two inches), and no necessity where the diameter is fairly low. It is very difficult to decide about the elective repair of aneurysms where the diameter is between 40mm and 50mm, he says.
To complicate matters, aneurysms do not have regular shapes, and it is therefore not possible to determine the maximum strains on the wall from the maximum diameter alone.
Liam Morris, Paul O'Donnell and McGloughlin, all from Caber, and Patrick Delassus of Galway-Mayo Institute of Technology have developed an experimental model for the evaluation of the stresses.
The model is made from an epoxy resin with similar mechanical properties to a damaged aorta. Water is pumped around the system at various rates, mimicking blood flow, and the model is lit with plane-polarised white light.
A reflective optical system then detects the patterns of stresses and strains shown by bands of light of different colours, and this information is saved on a camcorder.
Regions of high and low stress can be easily identified from the location and colours of the fringes, allowing the biomechanical engineer to provide guidance to the surgeon.
The inventors have filed for a patent on the reflective photoelastic modelling process.
Caber and Delassus have also conducted extensive research on new approaches to minimally invasive surgery in AAA stent grafting.
Stents, deployed inside an aneurysm to protect the weakened blood vessel wall, shorten hospital stays and recovery time, but they can also give rise to complications afterwards.
"Over a period of two years or so after the operation, the connection between the stent graft and the host artery can alter, and on occasion the stent graft can migrate," explains McGloughlin.
Morris says that the team expects that the new arrangement will cut down on clinically reported problems. Both projects have been supported by grants from Enterprise Ireland.