Motor cortex stimulation measured by magnetic resonance imaging on a standard 1.5 T clinical scanner

The authors report the effects of motor cortex stimulation of normal volunteers using conventional MR imaging techniques on a standard 1.5 T clinical scanner. A circular polarized head coil has been used normally for the stimulation measurements, although improvement in signal-to-noise ratio has been achieved by using a commercially available eye/ear surface coil with a loop of 8.5 cm in diameter. Magnet shimming with all first order coils was performed to the volunteer's head resulting in a magnetic field homogeneity of about 0.2 ppm. The imaging technique used was a conventional two-dimensional, first order flow rephased, gradient echo FLASH sequence with TR = 73 msec, TE = 60 msec, flip angle = 40 degrees. The stimulation experiments measured with the head coil were performed with a 64 x 128 matrix size, at a FOV = 230 mm, with NEX = 2 and 10 mm slice thickness. In case of stimulation measurements using the surface coil a 128 x 128 matrix size, a FOV = 200 mm, with NEX = 1 and a 5 mm slice thickness have been used. Total single scan time for one slice was 12 sec in both cases. The motor cortex stimulation was achieved by touching each finger to thumb in a sequential, self-paced, and repetitive manner. An increase in signal of order 4% in the motor cortex for the head coil measurements was observed, whereas of order 10% signal increase was detected for the surface coil measurements with smaller voxel size. The reported data demonstrate the technical feasibility of functional MR imaging using conventional sequences and equipment.