We propose a new functional MR method based on steady-state transmembrane water exchange rate measurements with diffusion exchange spectroscopy (DEXSY). Rapid DEXSY methods are implemented on a low-field MR system with a strong static gradient to test for an active component of water exchange in ex vivo neonatal mouse spinal cords. Temperature-dependent Arrhenius activation energies for water exchange are significantly greater in viable “live” samples than in the same samples after fixation, suggesting a connection to ATP-driven enzymatic processes. Moreover, exchange rates in live samples significantly decrease after blocking Na+/K+-ATPase pump activity, revealing an active component of water exchange.
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