Quantifying head motion associated with motor tasks used in fMRI

In functional magnetic resonance imaging (fMRI) studies, long experiment ti mes and small intensity changes associated with brain activation frequently lead to image artifacts due to head motion. Methods to minimize and correc t for head motion by restraint, fast imaging, and retrospective image regis tration are typically combined but do not completely solve the problem, par ticularly for specific patient populations. As an initial step toward optim izing future designs of head restraints and improving motion correction tec hniques, the head motion characteristics of groups of stroke subjects, age- matched controls, and young adults were investigated with the aid of an AIR simulator and a highly accurate position tracking system. Position measure ments were recorded during motor tasks involving either the hand or the foo t. Head motion was strongly dependent on the subject group and less upon th e task conditions based on ANOVA calculations (P < 0.05). The stroke subjec ts exhibited approximately twice the head motion compared to that of age-ma tched controls, and the latter's head motion was about twice that of young adults. Moreover, the range of head motion in stroke subjects over all task s was approximately 2 <plus/minus> 1 mm, with the motion occurring predomin antly as translation in the superior-inferior direction and pitch rotation (nodding). These results lead to several recommendations on the design of f MRI motor experiments and suggest that improved motion correction strategie s are required to examine such patient populations comprehensively. (C) 200 1 Academic Press.