Direct, longitudinal comparison of H-1 and Na-23 MRI after transient focalcerebral ischemia

Background and Purpose-Na-23 MRI may offer new insight into the evaluation of tissue injury. We performed a direct, longitudinal, morphological compar ison of H-1 T2 relaxation, H-1 apparent diffusion coefficient (ADC), Na-23 content, and histopathology after cerebral ischemia to address the hypothes es that (a) Na-23 MRI is unique in comparison to 1H MRI, and Cb) accumulati on of Na-23 is an unambiguous marker for dead tissue. Methods-Rats underwent 30 minutes of focal ischemia. MRIs of H-1 T2, H-1 AD C, and 23Na content were acquired from 12 hours up to 1, 2, or 14 days afte r reperfusion. On excision, brains were stained with triphenyltetrazolium c hloride (TTC). Results-In all cases, the region of abnormality increased in size for 2 day s. On day 5, both H-1 T2 and ADC temporarily appeared normal despite the pr esence of TTC-defined infarction. By comparison, the volume of tissue exhib iting abnormally intense Na-23 signal mirrored the TTC-defined infarct at a ll time points. Conclusions-Regions of high Na-23 content correlate well with the TTC-defin ed infarct and may be a quantitative in vivo marker for dead tissue. In con trast, the dynamics of the H-1 T2 and ADC make it difficult to interpret th ese images without additional information because they may appear normal de spite infarction. Neither type of'H image delineates dead tissue, and none of these methods predicts the potential infarct size at early time points.