Functional Magnetic Resonance Imaging (fMRI) - for the Psychiatrist


Magnetic Resonance Imaging (MRI) of the brain is well-recognized for its excellent spatial resolution, allowing neuroanatomic structures to be viewed in sharp detail. Recently, it has become possible to modify a conventional MRI scanner to study the brainís function as well. This new technology, called functional Magnetic Resonance Imaging (fMRI), has brain researchers excited for several reasons.

First, the most commonly used fMRI technique called BOLD-fMRI (Blood-Oxygen-Level-Dependent fMRI) potentially offers imaging with a temporal resolution on the order of 100 milliseconds and a spatial resolution of 1-2 millimeters, which is much greater than that of PET and SPECT scanning 1. This means that transient cognitive events can potentially be imaged and small structures like the amygdala can be more readily resolved. Next, unlike PET and SPECT, most fMRI techniques are noninvasive and do not involve the injection of radioactive materials so that a person can be imaged repeatedly. This may allow imaging of a patient repeatedly through different disease states (ie. imaging a bipolar patient through manic, depressive, and euthymic states) or developmental changes (ie. learning, cognitive stages of development, stages of grief recovery).

It also allows for investigations in healthy children due to the low risk. Third, with fMRI, one can easily make statistical statements in comparing different mental states within an individual in a single session whereas PET and SPECT scans usually rely on making statistical statements about group differences between mental states. Thus, fMRI may be of important use in understanding how a given individualís brain functions and perhaps, in the future, making psychiatric diagnoses and treatment recommendations. It is, in fact, already starting to being used in presurgical planning to map vital areas like language, motor function, and memory (see figure 1) 2-6. Perhaps most important for the future clinical utility of fMRI is that it involves only some upgrading of conventional MRI machines and, thus, may be become widely available.

Below, we describe the principles underlying the different types of functional MRI and give examples of how each technology can be used in psychiatry research or clinical practice. The basic principles underlying all types of MRI were discussed in the previous section on structural imaging. Namely, we discuss in this chapter the four main types of functional MRI:

(1) BOLD-fMRI which measures regional differences in oxygenated blood,
(2) perfusion fMRI which measures regional cerebral blood flow,
(3) diffusion-weighted fMRI which measures random movement of water molecules, and
(4) MRI spectroscopy which can measure certain cerebral metabolites noninvasively.


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