Abstract:

Computational fluid dynamic (CFD) simulations are emerging as a promising tool for diagnosis and treatment planning of vascular diseases such as intracranial aneurysms. In addition to the three-dimensional luminal geometry, prior knowledge of the blood velocity in the feeding artery is required before running a CFD simulation. This thesis describes a new method to extract the blood velocity in arteries using Digital Subtraction Angiography, a procedure routinely used in endovascular intervention. This method, referred to as the "radius-ratio" method, is based on the measurement of the contrast-intensity versus time at two locations along a vessel. The measured time-density curves are fitted to idealized curves that would result if contrast were convected in a fully developed steady pipe flow with an average velocity equal to the average velocity of the pulsatile flow. Centerline blood velocity is calculated by dividing the distance between the two vessel locations by the difference between the projected bolus arrival times at each location. Average velocity is then taken to be half this value. Compared to the existing time-density methods that extract velocity from angiography, the radius-ratio method is potentially more accurate because it incorporates a physics-based flow field model. To test the feasibility of the radius-ratio method in practical settings, the RR method was used to determine the velocity of blood in-vitro for vessel phantoms and in-vivo for canine and rabbit common carotid arteries. The RR computed velocity was then compared with the velocity computed using a standard time-density algorithm, and the velocity measured using an ultrasonic flowprobe. It was found that the accuracy v of both RR and TD methods were similar when compared when a gold standard flowprobe. To obtain a pulsatile canine waveform of velocity from the measured time-averaged velocity, an archetypal waveform in a canine common carotid artery can be scaled by heart rate and average velocity to yielding a approximation to the "true" velocity waveform. In human vasculature, it is postulated that the RR method is appropriate in internal carotid arteries and vertebral arteries.