In separate studies, researchers in the U.S. and Canada argue the use of 3-D computed tomography ahead of transcatheter aortic valve replacement should become standard. The 3-D imaging can more accurately assess aortic annulus size than echocardiographic tests, the researchers say. "The aortic annulus is not a circular structure, but elliptical. The larger dimension is not appreciated by 2-dimensional measurement," said Dr. Hasan Jilaihawi of Cedars-Sinai Heart Institute. However, physicians stress that echo screening does have advantages such as no radiation exposure or use of contract agents.