Abdominal Aortic Aneurysm (Aaa)
Abdominal Aortic Aneurysm (AAA) is still one of the leading causes of cardiovascular death in Westernized countries. The aorta is a major conduit of oxygenated blood to all the organs and limbs. AAA is a 'ballooning' of the aorta in the abdomen region that can dilate to 7 cm (the original diameter of the aorta is roughly 2 cm).
If left undetected, the AAA has the potential to rupture which would cause significant internal bleeding and eventual death without immediate attention.
Why does AAA rupture? This is the 'basic science' question that is being asked. If you blow up a balloon, why does it pop? Does it pop because you keep on adding pressure or does it pop because the material (rubber in this case) fails? The obvious answer is that there is a combination of both effects, but we want to understand which is more significant.
The lab published a paper in 2011 that investigated the difference of material properties between ruptured AAA tissue and unruptured AAA tissue. It was noted that ruptured AAA tissue was NOT weaker on average than unruptured AAA tissue. Although the sample size was small (n = 13, n_ruptured = 4, and n_unruptured = 9), this gave us an idea of the material properties differences between the two groups.
My Master's thesis investigated the effects of pressure on the ruptured and unruptured AAA. This was my first exposure to research as a grad student. I enjoyed the open ended problem solving that was required to make this project come to life. The research data was collected earlier with an American Heart Association grant along with a key collaborator, Dr. Erasmo Simão da Silva (cardio-thoracic surgeon at the University of São Paulo).
A very basic overview: 36 pictures were taken in 10 degree increments around each aneurysm. Each aneurysm had wall thicknesses measured in various locations and also material extension tests performed in various locations. I created a computational model that incorporated the 3D geometry from 2D images and all of the material properties (failure stress, material model coefficients and wall thicknesses) to create a model that would respond in a 'realistic' way.
If you made it this far on this page without dying of boredom, you can download the thesis here <- looking back, it could have been better written, but I suppose that this is a process of bettering oneself.
*There are treatments available for AAA. Hopefully I didn't scare you with the above description of AAA. We have come a long way in terms of treatment! Surgeons will opt to intervene when the AAA is greater than 5-5.5 cm in diameter (legacy standard).
The 'old' method of repair is known as aortic resection and the new method is known as endovascular grafting.
BRAIN ANEURYSM
Brain aneurysm is a dilation of a blood vessel in the brain. If the aneurysm ruptures, it can cause death or serious neurological damage to a patient through hemorrhagic stroke. When a brain aneurysm ruptures, blood starts to seep out and clot. Any additional fluid in the brain (not including the pre-existing cerebral fluid) increases the pressure in the brain because blood (and most fluids) are incompressible. If left untreated, the pressure will begin to shut down regions of the brain.
I worked on a mini project that looked to reconstruct 3D aneurysm geometries from bi-plane angiograms (*based on former lab-mates work: Gaurav Sharda Thesis). A bi-plane angiogram is a scan that takes two orthogonal views (or perpendicular) of an aneurysm.
The lab was working on a large 'legacy' data set from the International Study of Unruptured Intracranial Aneurysms (ISUIA) that tracked unruptured aneurysms (some went on to rupture). The idea was to take these two views and create an accurate 3D geometry. Gaurav did an awesome job on his project, I went ahead and added a mathematical equation that seemed to improve the reconstruction. I need to ask permission from the boss man to post pictures/equation <- awesome equation I promise!
*Treatment options are available through coil embolization or flow diverters.
The old school method is called surgical clipping. This involved a craniotomy along with a small 'clip' that clamped the aneurysm sac. Flow diverters are a relatively new and upcoming technology that surgeons seem to like.
There are currently efforts to produce different technologies that can treat aneurysms through 'non-traditional' (aforementioned) methods.