Effects of cerebral ischemic and reperfusion on T₂*- weighted MRI responses to brief oxygen challenge

This study characterized the effects of cerebral ischemia and reperfusion on T₂*-weighted magnetic resonance image (MRI) responses to brief oxygen challenge (OC) in transient (60 minutes) cerebral ischemia in rats. During occlusion, the ischemic core tissue showed no significant OC response, whereas the perfusion-diffusion mismatch tissue showed markedly higher percent changes relative to normal tissue. After reperfusion, much of the pixels with initial exaggerated OC responses showed normal OC responses, and the majority of these tissues were salvaged as defined by endpoint T₂ MRI. The initial core pixels showed exaggerated OC responses after reperfusion, but the majority of the core pixels eventually became infarct, suggesting exaggerated OC responses do not necessarily reflect salvageable tissue. Twenty-four hours after stroke, basal T₁ increased in the ischemic core. Oxygen challenge decreased T₁ significantly in the core, indicative of the substantial increases in dissolved oxygen in the core as the result of hyperperfusion. We concluded that exaggerated T₂*-weighted MRI responses to OC offer useful insight in ischemic tissue fates. However, exaggerated OC pixels are not all salvageable, and they exhibited complex dynamics depending on reperfusion status, hyperperfusion, and edema effects.