Cerebral activation using a MR-compatible piezoelectric actuator with adjustable vibration frequencies and in vivo wave propagation control

Functional magnetic resonance imaging (fMRI) studies are increasingly used in patients with brain tumors near the sensory motor cortex for planning of therapy. Passive stimuli can be helpful for reproducible results. The purpose of our study was to investigate frequency and amplitude dependencies of cerebral activation patterns using a vibratory stimulus that involves sensory and motor function and allows exact adjustment of vibratory frequencies and direct control of penetration depth into the tissue. Fifteen volunteers were studied with fMRI during vibratory stimulation of the right biceps muscle utilizing a block design (frequencies: 150 and 300 Hz, amplitudes: 400, 600, and 800 microm). In addition, visualization of the wave propagation into the biceps tissue itself was performed with a modified phase contrast sequence. A specially developed MR-compatible mechanical oscillator was used to apply the vibrotactile sensations. fMRI revealed activation of the left primary somatosensory cortex during application of both vibratory frequencies. Additionally, activity of the primary and supplementary motor cortex was revealed using 150-Hz stimuli, while only minimal at 300 Hz. The activity strength correlated with increasing stimulus amplitudes and the visualized penetration depth. Activation of motor areas was more pronounced at the beginning of the rest period. In conclusion, sensory motor areas can be activated using a piezoelectric actuator, with less pronounced motor area activation at higher frequencies. Our setup allowed local control of stimulus penetration through the tissue correlated to central activation, providing objective stimulus control. The pronounced activation of the motor cortex during the rest condition may reflect the subjective feeling of arm movement after the end of the stimulus.