Rapid MR imaging of a vascular challenge to focal ischemia in cat brain.

Deoxygenated blood was effectively used as a magnetic resonance (MR) susceptibility contrast agent to distinguish perfused and nonperfused (ischemic) regions in a focal ischemia model in cat brain at 2T. Modulation of cerebral blood oxygenation levels in response to apnea was followed in real time with T2*-weighted (gradient-recalled) echo-planar MR imaging. Signal loss in the T2*-weighted images occurred only in perfused tissues as blood became globally deoxygenated. These data complemented information from diffusion-weighted and contrast agent bolus-tracking images. In addition, observation of the signal recovery behavior on reventilation in both normal and ischemic brain offered potentially useful information about the state of the cerebral autoregulatory mechanism.