False cerebral activation on BOLD functional MR images: Study of low-amplitude motion weakly correlated to stimulus

BACKGROUND AND PURPOSE: Movements of the participant during blood oxygen le vel-dependent (BOLD) functional MR imaging cerebral activation studies are known to produce occasionally regions of false activation, especially when these movements are relatively large (>3 mm) and highly correlated with the stimulus. We investigated whether minimal (<1 mm), weakly correlated movem ents in a controlled functional MR imaging model could produce false activa tion artifacts that could potentially mimic regions of true activation in s ize, location, and statistical significance. METHODS: A life-size brain phantom was constructed by embedding vials of a dilute carboxylic acid solution within a gadolinium-doped gelatin mold, Ima ging was performed at 1.5 T using a 2D spiral sequence (3000/5 [TRITE]; fli p angle, 88 degrees; matrix, 64 x 64; field of view, 24 cm; section thickne ss, 5 mm). Controlled, in-plane, submillimeter movements of the phantom wer e generated using a pneumatic system and mere made to correlate with a hypo thetical "boxcar" stimulus over the range 0.31 < r < 0.96. Regions of false activation were sought using standard statistical methods (SPM96) that exc luded phantom edges and accounted for spatial extent (regions tested at P < .05, corrected for multiple comparisons). A similar experiment was perform ed on a resting volunteer. RESULTS: The pneumatic system provided motion control with average in-plane displacements and rotations of 0.74 mm and 0.47 degrees, respectively, in the 18 data sets analyzed. No areas of false activation in the phantom were identified for poorly correlated motions (r < 0.52). Above this level, fal se activations occurred with increasing frequency, scaling in size and numb er with the degree of motion correlation, For motions with r > 0.67, areas of false activation were seen in every experiment. For a statistical thresh old of P = .001, the median number of falsely activated regions was 3.5, wi th a mean size of 71.7 voxels (approximately 5 cc). Areas of possibly false activation of average size 72.5 voxels resulting from passive motion of th e resting human participant were observed in two of four experiments. CONCLUSION: Participant movements of 1 mm or less that are only modestly co rrelated with a blocked stimulus paradigm can produce appreciable false act ivation artifacts on BOLD functional MR imaging studies, even when strict i mage realignment methods are used to prevent them.