CONTEXTUAL DETECTION OF FMRI ACTIVATIONS AND MULTIMODAL ASPECTS OF BRAIN IMAGING

Functional magnetic resonance imaging (fMRI) is a non-invasive method which can be used to indirectly localize neuronal activations in the human brain. Functional MRI is based on changes in the blood oxygenation level near the activated tissue. In an fMRI experiment, a stimulus is given to a subject or the subject is asked to conduct a physical or cognitive task. During the experiment, a nuclear magnetic resonance signal is measured outside the head, and time series of three-dimensional image volumes are constructed. The object of this thesis is to study the localization of activation regions from the constructed time series as well as multimodal aspects of brain imaging. The localization of activation regions typically consists of the following phases: preprocessing of the four-dimensional spatiotemporal data, computation of a statistic image, and detection of statistically significantly activated regions from the statistic image. The statistic image is a three-dimensional map, which shows the statistical significance of the measured experimental effect at voxel level. The detection and localization of the activated regions can be carried out by segmenting the statistic image into activated and non-activated regions. The segmentation is difficult because the statistic image