Sodium and potassium MRI in cerebral ischemia

Abstract

Ischemia can be accompanied by dramatic disturbances in the tissue ion balance. This chapter reviews the mechanisms of brain Na+/K+ imbalance in ischemia, their implications for using magnetic resonance imaging (MRI) for basic understanding, diagnostics, and therapy of stroke, as well as MRI challenges and experimental approaches. Experimental stroke studies demonstrated the potential of 23Na MRI to determine stroke onset time, which is critical for compliance with the time window for thrombolysis. 23Na MRI revealed heterogeneity in the time of the beginning and the rate of increase in the Na+ content within the ischemic core and between cortical and subcortical areas in the rat brain, with the maximum rate of Na+ accumulation at the periphery of the ischemic core. K+ in ischemic rat brain has been assessed by K/Rb substitution and 87Rb MRI. Multiquantum filtering techniques have a capability to discriminate between intra- and extracellular cations. 23Na MRI techniques are directly transferable to the clinical setting, although one might anticipate a significant heterogeneity of the human stroke progression compared to the animal models. It is expected that estimates of brain Na + and K + by MRI could provide an enhanced physiological characterization of ischemic lesion and may be helpful for assessing tissue viability and amenability to therapy and outcome prognosis.