FUNCTIONAL MR-IMAGING OF VISUAL AND MOTOR CORTEX STIMULATION AT HIGH TEMPORAL RESOLUTION USING A FLASH TECHNIQUE ON A STANDARD 1.5-TESLA SCANNER

Functional magnetic resonance imaging (MRI) was performed on a convent ional 1.5 T scanner by means of a modified FLASH-technique at temporal resolutions of 80 and 320 ms. The method's stability was assessed by phantom measurements and by investigation of three volunteers resultin g in a low amplitude (3%) periodic (4 s) signal modulation for the in vivo measurements, which was not observable in the phantom experiments . fMRI activation studies of motor and visual cortices of four adjacen t slices were carried out on 12 healthy right-handed volunteers. Stimu lation was performed by a triggered single white light flash or single finger-to-thumb opposition movement, respectively. Event-related resp onse of visual and motor activation was traced over 10.24 s with a tem poral resolution of 320 ms for the four slice measurements. Brain acti vation maps were calculated by correlation of measured signal time cou rses with a time-shifted boxcar function. Activation was quantified by calculation of percentual signal change in relation to the baseline. Observed signal magnitudes were about 5-7% in visual and about 8-12% i n primary motor cortex. While photic response was delayed by about 2 s , motor stimulation showed an instantaneous increase of the MR signal. MR signal responses for both stimuli had decayed completely after abo ut 5 s. Our results show that event-related fMRI enables mapping of br ain function at sufficient spatial resolution with a temporal resoluti on of up to 80 ms on a conventional scanner.