A Primer on MRI and Functional MRI

by Douglas C. Noll.

Functional brain mapping with magnetic resonance imaging (MRI) is a rapidly growing field that has emerged in only the past several years. Functional MRI (fMRI) is the use of MRI equipment to detect regional changes cerebral metabolism or in blood flow, volume or oxygenation in response to task activation. The most popular technique utilizes blood oxygenation level dependent (BOLD) contrast, which is based on the differing magnetic properties of oxygenated (diamagnetic) and deoxygenated (paramagnetic) blood. These magnetic susceptibility differences lead to small, but detectable changes in susceptibility-weighted MR image intensity. Relatively low image signal-to-noise ratio (SNR) of the BOLD effect, head movement, and undesired physiological sources of variability (cardiac, pulmonary) make detection of the activation-related signal changes difficult. Fortunately, rapid image acquisition techniques can be used to generate data sets with hundreds of images for each slice location which can be statistically analyzed to determine foci of brain activity. Finally, the basic properties of the human activation response have implications for experimental design and statistical processing techniques used for extraction of functional information from the four-dimensional data sets. [via]

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