Spatial-temporal MRI Responses of Stroke Rats to Oxygen Challenge

INTRODUCTION Therapy in acute ischemic stroke can only be effective as long as potentially salvageable tissue is present within the brain area affected by the blood flow disturbance. Therefore, the identification of the penumbra and the distinction of this potentially reversible condition from irreversibly damaged tissue are of utmost importance for the initiation of treatment strategies. Irreversible tissue damage and penumbra can be reliably identified by multitracer positron emission tomography which has severe limitations due to complexity, invasiveness and radiation exposure (1). Mismatch of diffusion/perfusion by MRI has been used as an estimate of the ischemic penumbra (2). But it has been reported that large parts of the mismatch region appear not to be at risk, even though they may contribute to functional impairment (3). Beside perfusion deficit, a marker of metabolism is essential to better define penumbra. In this study, we employed T2*-weighted (T2*W) BOLD fMRI of oxygen challenge (OC) as a mean to probe tissue status associated with acute stroke. This approach was evaluated in permanent middle cerebral artery occlusion (MCAO) in rats. Along with diffusion and perfusion MRI to identify mismatch, we analyzed the spatiotemporal evolution of the BOLD fMRI responses to OC.