Principles and Clinical Applications of Functional Brain Imaging

Abstract

Functional imaging techniques are well established in both the nuclear medicine and positron emission tomography (PET) communities. While the informational content of these images can be high, limited availability (PET) and low spatial resolution limit their clinical applications. Magnetic resonance (MR) imaging can provide both functional and anatomic information, in part because of the large number of intrinsic parameters that affect MR image contrast. These include proton density (r), relaxation times T₁ and T₂, chemical shift, flow, magnetic susceptibility, diffusion, and others. While not functions of tissue per se, each of these parameters can be exploited to assess various functional activities of the body. This is best illustrated by MR angiography, where both time-of-flight and phase contrast methods depend on velocity (cardiovascular function) to provide contrast and thereby to represent vascular anatomy. Similarly, it can be argued that a positive gadolinium-diethylenetriaminopentoacetic acid (Gd-DTPA) central nervous system (CNS) examination reflects abnormal function (or integrity) of the blood-brain barrier.