Functional neuro-imaging with magnetic resonance elastography

Abstract

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. The first mechanism was ruled out based on results from an additional experiment where hypercapnia was induced to cause vasodilation. This implies the mechanism responsible is a primary measure of neuronal activation.