Obtaining accurate patient-specific blood flow information is essential for understanding cardio-vascular pathologies and predicting their onset. To date there are no clinical tools available for effciently measuring these complex flow patterns in-vivo. Phase Contrast Magnetic Resonance Imaging (PC-MRI) can be used as it is able to measure time-resolved three dimensional flow fields non-invasively, however it has limited resolution and suffers under low signal to noise ratio, in particular at low flow velocities. In order to overcome these limitations one can use Computational Fluid Dynamics (CFD) in conjunction with medical imaging so as to obtain highly resolved time-dependant flow fields. This offers many advantages as it allows for any desireable level of detail and gives access to a wealth of data which typically cannot be measured directly. Adding one level of complication, a full fluid-structure interaction model can be used to obtain the response of the wall as well as the blood flow dynamics. Our work focusses on combining these CFD simulations with MRI measurements so as to provide high quality patient-specific blood flow information.