Contrast Agents for Magnetic Resonance Imaging

The alteration of signal intensity in diseased tissue forms the basis for magnetic resonance (MR) imaging in diagnostic radiology. Tissue signal intensity observed in MR images is the result of a complex interaction of numerous factors, which can be classified as those that reflect intrinsic properties of biologic tissues, e.g., T1 and T2 relaxation times and proton density, and those that are equipment related, e.g., field strength or pulse sequences. However, due to a wide biologic varia-tion, relaxation times of normal and abnormal tissues overlap. This limits the ability of plain MR to detect and, even more, to characterize abnormal tissue. By using very specialized pulse sequences, only some of these limitations can be overcome. An alternative solution is provided by MR contrast agents, which alter tissue relaxation times and can, therefore, be used to manipulate their signal intensity.