Subject motion is the most common artefact and has two components: voluntary and involuntary (physiological). The result of voluntary motion during acquisition may be an obvious blurring (Plate.. . Z). The co-operation of subjects is vital and special regard is required for children, the elderly, and those with neurological or psychiatric disorders who may find the MRI environment disconcerting. The subject's head is physically restrained by additional padding and by Velcro straps placed across the forehead. Involuntary motion arises primarily from the cardiorespiratory cycle causing pulsation of the blood vessels and cerebrospinal fluid. This is most apparent in structural images showing major arteries.
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