Transcatheter aortic valve implantation (TAVI) is an emerging alternative therapy for aortic stenosis for patients ineligible for open heart surgery or at high risk for perioperative complications. Pre-procedural imaging of the aortic root is essential for selection of the correct valve prosthesis and to minimize complications as prosthesis mismatch, possibly subsequent embolization, coronary obstruction, annulus rupture or severe aortic regurgitation. The aim of the study is to compare the different imaging modalities for aortic root measurements. Aortic root imaging will be performed prior to TAVI-procedure. The contrast injection will be performed either into the aorta or into the left ventricle. The datasets will be assessed by blinded-independent observers in a multi-planar reconstruction view. The study will be performed retrospectively (2009-2012) and prospectively starting 2013.