Functional neuro-imaging with magnetic resonance elastography

Evaluate changes in the shear modulus of brain tissue as a new measure of localized brain function. A spin-echo magnetic resonance elastography (MRE) sequence was modified to allow two interleaved paradigms: stimulus ON/OFF. To avoid neuronal habituation, a paradigm was active for 9s before switching to the other paradigm. After each paradigm switch, a period of 1.8 s was allowed for hemodynamic equilibrium. Seven healthy black mice were studied. An electrical current to the hind limb, ~1 mA, 3 Hz, pulse width ~250 ms, was used as the functional stimulus. A separate control scan was also performed where no stimulus was applied for either paradigm. Vibration frequency = 1kHz. In six of the seven animals, a localized increase in G’ was observed in the somatosensory and motor cortex areas, whereas no difference was observed in the control scan. The average increase of G’ = 14%. Two potential mechanisms were considered: (i) a vascular effect similar to BOLD in fMRI and (ii) calcium influx into the neurons. Th...