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 conventional 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 resulting 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 adjacent slices were carried out on 12 healthy right-handed volunteers. Stimulation was performed by a triggered single white light flash or single finger-to-thumb opposition movement, respectively. Event-related response of visual and motor activation was traced over 10.24 s with a temporal resolution of 320 ms for the four slice measurements. Brain activation maps were calculated by correlation of measured signal time courses 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% in 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 about 5 s. Our results show that event-related fMRI enables mapping of brain function at sufficient spatial resolution with a temporal resolution of up to 80 ms on a conventional scanner.