Basis of MR angiography. An introduction

Contrast MR imaging is based on the physical properties of biological tissues, such as relaxation times T1 and T2 and proton density. On particular, however, the motion of protons will affect image quality in MRI, resulting in severe image artifacts. There are two types of flow phenomens, referred to as time-of-flight (TOF) and phase effects. In the past several techniques have been developed in order to eliminate or compensate for any artifacts related to the flow effects. On the other hand, it is also possible to make use of flow effects for the purpose of flow visualization. These techniques are commonly referred to as MR angiography. Depending on the flow effect used, there are two types of MR angiography techniques currently available: TOF and phase contrast MR angiography. Each of the techniques makes use of one effect and suppresses the other one as much as possible. The purpose of this paper is to review the underlying physical principles of MR angiography and to show the clinical applications for it. (orig.)