Contrast agents have greatly expanded the role of MR imaging (MRI) to allow assessment of physiologic, or "functional," parameters. Although activation mapping generally does not require contrast agents, other forms of functional MRI, including mapping of cerebral hemodynamics (eg, perfusion imaging), are best done with the use of contrast agents. Serial echo planar images are obtained after bolus injection of lanthanide chelates. Application of susceptibility contrast physics and standard tracer kinetic principles permits generation of relative cerebral blood volume maps.