FREQUENCY-DEPENDENT CHANGES OF REGIONAL CEREBRAL BLOOD-FLOW DURING FINGER MOVEMENTS - FUNCTIONAL MRI COMPARED TO PET

To evaluate the effect of the repetition rate of a simple movement on the magnitude of neuronal recruitment in the primary sensorimotor cort ex, we used a blood flow-sensitive, echo planar functional magnetic re sonance imaging (fMRI) sequence in six normal volunteers. Three of the volunteers also had [O-15]water positron emission tomography (PET) st udies using the same paradigm. Previous PET studies had shown an incre ase in regional CBF (rCBF) with movement frequencies up to 2 Hz and th en a plateau of regional cerebral blood flow (rCBF) at faster frequenc ies. To evaluate the extent of the activation, the correlation coeffic ient (cc) of the Fourier-transformed time-signal intensity change with the Fourier-transformed reference function was calculated pixel by pi xel. The degree of activation was measured as the signal percent chang e of each region of interest with a cc > 0.5. The left primary sensori motor cortex was constantly activated at 1, 1.5, 2, and 4 Hz, while th ere was only inconsistent activation at 0.25 and 0.5 Hz. Percent chang e in signal intensity linearly increased from 1 to 4 Hz. Area of activ ation increased up to 2 Hz and showed a tendency to decrease at higher frequencies. Individual analysis of PET data showed activation in the same location as that revealed by fMRI. The combination of progressiv ely increasing signal intensity with an area that increases to 2 Hz an d declines at faster frequencies explains the PET finding of plateau o f rCBF at the faster frequencies. Functional magnetic resonance imagin g shows similar results to PET, but is better able to dissociate area and magnitude of change.