MR FLOW QUANTIFICATION WITH CARDIOVASCULAR APPLICATIONS - A SHORT OVERVIEW

We present a short overview of the potential of magnetic resonance ima ging (MRI) for quantification of flow in the cardiovascular system. Th e most widespread method for creation of MRI flow information utilizes flow-sensitizing magnetic field gradients. Objects that move in the v arying magnetic field introduced by such gradients change their preces sion frequency and therefore obtain a velocity-dependent offset phase angle. The exact phase behaviour for different types of gradients and motion patterns can be calculated and a very simple linear relationshi p is predicted by theory as well as confirmed in experiments between c onstant velocity and phase angle. Phase-sensitive flow MRI (velocity m apping) is frequently performed as a two-dimensional gradient-echo tec hnique with flow sensitivity (flow encoding) in the through-plane dire ction, but other encoding directions are possible. Parameters that can be determined from a velocity map are linear velocity in each voxel, vessel area and flow rate. In the case of a stenotic vessel, the trans -stenotic pressure gradient can also be estimated. The velocity mappin g method has been extensively used for cardiac flow studies in adult p atient groups, e.g. for indirect measurements of coronary artery flow and for the study of aortic valve diseases. In children, the method ha s recently been used to determine shunt volumes in congenital heart di sease. We conclude that flow investigations with MRI may in the future present a good alternative for the clinical evaluation of cardiovascu lar disorders.