A 61-year-old male patient with right hemiparesis imaged at 2 A 61-year-old male patient with right hemiparesis imaged at 2.3 hours and 3 days. A 61-year-old male patient with right hemiparesis imaged at 2.3 hours and 3 days. Abnormal areas are outlined on CBV (A), CBF (B), and follow-up CT (C) images. After coregistration, we defined 3 regions on CBF maps (D): region 1 (red), “infarct core”—abnormal on CBV, CBF, and follow-up CT images; region 2 (blue), “penumbra that infarcts”—normal on CBV but abnormal on CBF and follow-up CT images; and region 3 (green) “penumbra that recovers”—abnormal on CBF but normal on CBV and follow-up CT images. P.W. Schaefer et al. AJNR Am J Neuroradiol 2006;27:20-25 ©2006 by American Society of Neuroradiology