Microstructure and exchange are not always linked

Motivation: To understand the mechanisms of water exchange. Goal(s): To determine the extent that DEXSY-based water exchange measurements depend on changes to tissue microstructure (e.g., cellular swelling/shrinking). Approach: NMR measurements of ADC, exchange rate and light microscopy measurements of intrinsic optical signal (IOS) are acquired simultaneously in real time on viable and dead ex vivo neural tissue during potassium and osmotic perturbations. Results: In dead samples, exchange, ADC, and IOS are similarly affected. In viable samples, however, some perturbations affect exchange differently than they do the ADC and IOS that reflect changes in microsctructure alone. Exchange may be physiologically regulated independently of cell volume. Impact: Water exchange is sensitive to cellular processes distinct from microstructure and blood flow. This measurement possibly could lead to a new fMRI method.