Clinical Applications of MR Perfusion Imaging

Several techniques are available for assessing brain perfusion or hemodynamics in the clinical setting, in general falling into two basic categories: those using diffusible and those using nondiffusible tracers. H 215O PET, 99mTc-HMPAO or 99mTc-ECD single photon emission computed tomography, stable xenon computed tomography (CT), and arterial spin-labeled (ASL) MRI are examples of diffusible tracer techniques, where the tracer is not confined to the vessels and enters the tissue. The major nondiffusible tracer techniques in use are bolus contrast CT and MR perfusion methods, where the tracer remains within the vasculature as long as the blood–brain barrier is intact. Clinical experience in MRI is greatest for bolus contrast or dynamic susceptibility contrast perfusion MRI, although the use of dynamic contrast-enhanced and ASL techniques is increasing. Each MRI-based technique has advantages and disadvantages, which are discussed briefly in this chapter and in greater depth in chapters elsewhere in this book. Improvements in acquisition and postprocessing strategies over the last several years have made efficient implementation of both approaches a reality, not only in clinical trials but also in routine daily clinical practice with practical utility of perfusion methodology demonstrated for several applications such as acute and chronic cerebrovascular disease, central nervous system neoplasms, epilepsy, and aging and neurodegenerative disorders. This chapter focuses primarily on these clinical applications, using selected examples to illustrate strengths, weaknesses, or complementary roles of different MR perfusion techniques.