Functional 2D and 3D magnetic resonance imaging of motor cortex stimulation at high spatial resolution using standard 1.5 T imager.

This paper reports the effects of motor cortex stimulation of normal volunteers using conventional MR imaging techniques on standard 1.5 T clinical scanner. Improvement in signal-to-noise (S/N) 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 0.1-0.2 ppm. The imaging technique used was an optimized conventional 2D and 3D, first order flow rephased, gradient-echo sequence (FLASH) with fat-suppression and reduced bandwidth (16-28 Hz/pixel) and TR = 80-120 ms, TE = 60 ms, flip angle = 40 degrees, matrix = 128 x 128, FOV = 150-250 mm, slice-thickness = 2-5 mm, NEX = 1, and a total single scan time for one image of about 12-16 s. In the 3D FLASH measurements, a slab of 32 mm thickness with 16 partitions was evaluated. The motor cortex stimulation was achieved by touching each finger to thumb in a sequential, self-paced, and repetitive manner. During stimulation, an increase in signal of order 10-20% was detected in the motor and sensory cortex due to reduced partial volume effects and optimized S/N for the measurements at small voxel size. 3D FLASH imaging at high spatial resolution shows good anatomical correlation of signal increase with gray matter of the motor and sensory cortex. The reported data demonstrate the technical feasibility of functional 2D and 3D MR imaging at high spatial resolution using optimized conventional sequences and equipment.