Abstract #4910

Apparent Population Inversion Due to Steady-State Transcytolemmal Water Exchange

Xin Li¹, Silvia Mangia², Jing-Huei Lee³, Ruiliang Bai⁴, and Charles S. Springer¹

¹Advanced Imaging Research Center, Oregon Health & Science University, Portland, OR, United States, ²Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States, ³Biomedical Engineering, University of Cincinnati, Cincinnati, OH, United States, ⁴Interdisciplinary Institute of Neuroscience and Technology, Zhejiang University, Hangzhou, China

The homeostatic cellular water efflux rate constant, k_io, has a significant contribution from cell membrane sodium pump activity previously unmeasurable. With high extracellular contrast agent concentration or ultra-low magnetic field, k_io can be precisely determined by two-site-exchange analysis of in vivo ¹H₂O longitudinal relaxation data. With the low field case, there is an inversion of the apparent tissue compartmental contributions from the true values. The NMR shutter-speed organizing principle informs an analysis spanning the entire range of conditions.

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