fMRI: Clinical and Research Applications

Functional Magnetic Resonance Imaging (fMRI) has become the most popular method for assessing major facts of functional brain topography for both research and clinical purposes. fMRI is a powerful non-invasive tool in the study of the function of the brain, used, for example, by psychologists, psychiatrists, neurologists and neuroscientists [2]. fMRI is a technique that uses magnetic resonance imaging to measure brain activity by measuring changes in the local oxygenation of blood, which in turn reflects the amount of local brain activities. While this technique has the advantages of high spatial resolution and non-invasive nature, it has a low temporal resolution respect to other brain imaging techniques. This is because it is not a direct measure; it only measures the secondary physiological correlates of neural activity. fMRI uses the contrast mechanisms which are correlated to physiological changes in local regions of the brain. The first mechanism used for fMRI is Blood Oxygenation Level-Dependent (BOLD) contrast [3] and the second contrast mechanism is the perfusion contrast obtained using Arterial Spin Labeling (ASL). The ASL uses magnetically labeled arterial blood water as a flow tracer [4]. As compared to the BOLD contrast, that is most useful for detecting dynamic changes in brain activity over short time periods (seconds to minutes), ASL is most useful for characterizing resting states, particularly in pathological conditions that affect C erebral Blood Flow (CBF), such as cerebrovascular disease, or for measuring slow variations in CBF or neural activity that occur over long periods. fMRI can give high quality visualization of the location of activity in the brain resulting from motor or sensory stimulation or cognitive functions [5]. It therefore allows the study of how the healthy brain functions is affected by different diseases, how it attempts to recover after damage and how drugs can modulate activity or post-damage recovery and how cognitive states are encoded by the brain activities.