Contrast Agents

Abstract

There is a variety of MR contrast media, but we will deal exclusively with paramagnetic agents carrying gadolinium (Gd). These compounds are scheduled for intravenous use both in MRI and MRA. Gd is a metal with a very strong magnetic dipole moment facilitating both T1 and T2 relaxation of protons in its immediate vicinity. Simultaneous shortening of T1 and T2 produces conflicting effects. In most tissues T1 exceeds by far T2 and the absolute changes in T1 override the counteraction of T2 shortening. Thus, after Gd infusion it is necessary to obtain T1w sequences and to look for hyperintensity as a sign of contrast accumulation.