Hemodynamic measurements and vessel wall property assessment in patients with abdominal aortic aneurysm during pre-operative dynamic MRI examinination.

An abdominal aortic aneurysm (AAA) is a dilatation of the abdominal part of the
aorta of more than 50% in diameter. The risk of the dilated aorta is that the
expansion progresses to the level that it may rupture. When rupture occurs a
life threatening situation develops rapidly. The prevalence of an AAA in people
over 60 years increased from 9 AAAs per 100.000 inhabitants in the 1960*s to 38
AAAs per 100.000 inhabitants in 1990-2000.1 Treatment of the AAA is indicated
if the risk of rupture outweighs the risk associated with surgical
intervention. So far the most common method to estimate the risk of rupture is
based on the maximal diameter of the aneurysm. If the maximal diameter of the
AAA is over 5 cm, surgery is indicated. However, some AAAs with smaller
diameters also rupture while some with larger diameters do not.2 Thus the
maximum diameter is an inaccurate predictor of rupture.

To assess the influence of bloodpressure, wall thickness, wall properties, and
geometry changes throughout the cardiac cycle on the wall stress calculations.
Previous analysis were performed with an assumed bloodpressure value, an
uniform wall thickness, wall properties, and a static geometry obtained from a
arbitrary time-point in the cardiac cycle. The geometry itself together with
the actual bloodpressure are the major factors determining the level of
wallstress. By doing so the potential advantages of dynamic imaging against
non-triggered conventional CT, will be assessed. Dynamic MRI scanning (geometry
and volume changes of the AAA during the heart cycle) and the intra-arterial
pressure measurement represents the single combination to calculate in vivo the
patient's specific wall properties,which can be used in the wall stress
calulations.

The dynamic geometry is extracted from MRI-scan data. The geometry itself is
dependent on the current blood pressure. It has been documented that during MRI
scanning the blood pressure demonstrates considerable variation. For example
the blood pressure will decrease when the patient falls asleep, which during
MRI scanning is not infrequent. On the other hand, blood pressure can rise as
the result of physiological stress caused by the scan and the expectation of
surgery.

A total number of 10 patients will who are on the waiting list for elective
endovascular treatment of their AAA will undergo a MRI examination with
intravascular blood pressure measurements.

The risk related to the invasive pressure measurements are comparable with the
risks that are related to a (heart) catheterization. These are small in
experienced hands.