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 v olunteers using conventional MR imaging techniques on standard 1.5 T c linical scanner. Improvement in signal-to-noise (S/N) ratio has been a chieved 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 h omogeneity of about 0.1-0.2 ppm. The imaging technique used was an opt imized conventional 2D and 3D, first order flow rephased, gradient-ech o sequence (FLASH) with fat-suppression and reduced bandwidth (16-28 H z/pixel) and TR = 80=120 ms, TE = 60 ms, flip angle = 40 degrees, matr ix = 128 x 128, FOV = 150-250 mm, slice-thickness = 2-5 mm, NEX = 1, a nd a total single scan time for one image df about 12-16 s. In the 3D FLASH measurements, a slab of 32 mm thickness with 16 partitions was e valuated. The motor cortex stimulation was achieved by touching each f inger to thumb in a sequential, self-paced, and repetitive manner. Dur ing stimulation, an increase in signal of order 10-20% was detected in the motor and sensory cortex due to reduced partial volume effects an d optimized S/N for the measurements at small voxel size. 3D FLASH ima ging at high spatial resolution shows good anatomical correlation of s ignal increase with gray matter of the motor and sensory cortex. The r eported data demonstrate the technical feasibility of functional 2D an d 3D MR imaging at high spatial resolution using optimized conventiona l sequences and equipment.