Oxygen Metabolism in Ischemic Stroke Using Magnetic Resonance Imaging

Detecting "at-risk" but potentially salvageable brain tissue, known as the ischemic penumbra, is of importance for identifying patients who may benefit from thrombolytic or other treatments beyond the currently FDA-approved short therapeutic window for tissue plasminogen activator. Since the magnetic resonance blood oxygenation level-dependent (BOLD) contrast may provide information concerning tissue oxygen metabolism, its utilization in ischemic stroke has been explored. The focus of this review is to provide an introduction of several BOLD-based methods, including susceptibility-weighted imaging, R2 BOLD, R2*, R2′, MR_OEF, and MR_OMI approaches to assess cerebral oxygenation changes induced by ischemia. Specifically, we will review the underlying pathophysiological basis of the imaging approaches, followed by a brief introduction of BOLD contrast, and finally the applications of BOLD approaches in ischemic stroke. The advantages and disadvantages of each method are addressed. In summary, the BOLD-based methods are promising for imaging oxygenation in ischemic tissue. Future steps would include technical refinement and vigorous validation against another independent method, such as positron emission tomography.