Data analysis

General principles of data analysis are reviewed here; for more detailed coverage of the issues and the methods implemented in a variety of software packages, see the reviews by Lange(9) and Rabe-Hesketh et al.(19 Movement estimation and correction

The first step in fMRI data analysis is to estimate the extent of head motion during data acquisition and to correct it. ^„P Gross head movement (of several millimetres) can be detected simply by viewing the images acquired over time at a given slice. However, because of the multislice acquisition protocols generally used for fMRI, the magnetic field to which the brain is exposed will change dramatically within the space of a few micrometres at the superior and inferior edges of a selectively irradiated slice. This means that minute head movements (< 1 mm) can have disproportionately large effects on magnetic resonance signal emission.

Head movement occurring at the same time as experimental stimuli are presented, namely stimulus correlated motion, can artefactually exaggerate the neurovascular response. Head movement occurring randomly with respect to the experimental design is more likely to cause the opposite problem of artefactually attenuating the measured response. Therefore it is essential to supplement visual inspection of the data by computerized methods for movement estimation and its correction.

Pregnancy And Childbirth

Pregnancy And Childbirth

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