Background: Perfusion computed tomography (CT) is an evolving technique in the diagnosis of acute stroke. After complex deconvolution algorithms, perfusion color maps-cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT)— are produced, they give visual confirmation of perfusion deficit in ischemic area, but some discrepancies exist regarding this technique in reliability of quantitative detection of tissue viability: penumbra (tissue at risk) that surrounds core (necrosis). Purpose: The purpose of this prospective study was to define brain tissue viability grade on the basis of the perfusion CT parameters in acute stroke patients. Material and Methods: Multimodal CT imaging protocol (unenhanced CT of the brain, CT angiography of head and neck blood vessels, followed by brain perfusion CT and 24 hours follow-up brain CT) was performed. Perfusion deficit was detected first visually, with subsequent manual quantitative and relative measurements in affected and contra-lateral hemisphere in 87 patients. Results: Visual perfusion deficit on perfusion CT images was found in 78 cases (38 female, 40 male; mean age 30 - 84 years): penumbra lesion (n = 49) and core lesion (n = 42). Both lesion types were detected by increased MTT on perfusion CT map, penumbra area showed mean values 202.40% (113% - 345% ± 57.17) and core (41% - 320% ± 64.53) in comparison to contra-lateral hemisphere. CBV mean values in penumbra group were increased up to 113.10% (45% - 276% ± 36.29) and in core decreased till 41.82% (3% - 107% ± 27.09). CBF values were decreased up to 65.63% (31% - 137% ± 22) in penumbra lesion and markedly decreased till 25.94% (4% - 79% ± 17.35) in core. Conclusion: Our study shows that perfusion CT measurements relative threshold values are recommended in definition of penumbra and core lesions in acute stroke patients.
 Wintermark, M., Maeder, P., Thiran, J.P., Schnyder, P. and Meuli, R. (2001) Quantitative assessment of regional cerebral blood flows by perfusion CT studies at low injection rates: A critical review of the underlying theoretical models. European Radiology, 11, 1220-1230. doi:10.1007/s003300000707
 Kudo, K., Terae, S., Katoh, C., et al. (2003) Quantitative cerebral blood flow measurement with dynamic perfusion CT using the vascular-pixel elimination method: Comparison with H2 (15) O positron emission tomography. American Journal of Neuroradiology, 24, 419-426.
 Wintermark, M., Fralnders, A.E., Velthuis, B., et al. (2006) Perfusion-CT assessment of infarct core and penumbra: Receiver operating characteristic curve analysis in 130 patients suspected of acute hemispheric stroke. Stroke, 37, 979-985. doi:10.1161/01.STR.0000209238.61459.39
 Wintermark, M., Lau, B.C., Chien, J. and Arora, S. (2008) The anterior cerebral artery is an appropriate arterial input function for perfusion-CT processing in patients with acute stroke. Neuroradiology, 50, 227-236. doi:10.1007/s00234-007-0336-8
 Konstas, A.A., Goldmakher, G.V., Lee, T.Y. and Lev, M.H. (2009) Theoretic basis and technical implementations of CT perfusion in acute ischemic stroke. Part 1. Theoretic basis. American Journal of Neuroradiology, 30, 662-668. doi:10.3174/ajnr.A1487
 Kamalian, S., Maas, M.B., Goldmacher, G.V., et al. (2011) CT cerebral blood flow maps optimally correlate with admission diffusion-weighted imaging in acute stroke but thresholds vary by postprocessing platform. Stroke, 42, 1923-1932. doi:10.1161/STROKEAHA.110.610618
 Jauch, E.C., Saver, J.L., Adams, H.P., Bruno, A., Connors, J.J. and Demaerschalk, B.M. (2013) Guidelines for the eraly management of patients with acute ischemic stroke: A guideline for healthcare professionals from the American Heart Association/American Stroke Association. Stroke, 44, 870-974. doi:10.1161/STR.0b013e318284056a
 Ebinger, M., De Silva, D.A., Christensen, S., et al. (2009) Imaging the penumbra—Strategies to detect tissue at risk after ischemic stroke. Journal of Clinical Neuroscience, 16, 178-187. doi:10.1016/j.jocn.2008.04.002
 Murphy, B.D., Fox, A.J., Lee, D.H., et al. (2008) White matter thresholds for ischemic penumbra and infarct core in patients with acute stroke: CT perfusion study. Radiology, 247, 818-25. doi:10.1148/radiol.2473070551
 Schaefer, P.W., Roccatagiata, L., Ledezma, C., et al. (2006) First-pass quantitative CT perfusion identifies thresholds for salvageable penumbra in acute stroke patients treated with intra-arterial therapy. American Journal of Neuroradiology, 27, 20-25.
 Bivard, A., McElduff, P., Spratt, N., et al. (2011) Defining the extent of irreversible brain ischemia using perfusion computed tomography. Cerebrovascular Diseases, 31, 238-244. doi:10.1159/000321897
 Wintermark, M., Rechhart, M., Thiran, J.P., et al. (2002) Prognostic accuracy of cerebral blood flow measurement by perfusion computed tomography, at the time of emergency room admission, in acute stroke patients. Annals of Neurology, 51, 417-432. doi:10.1002/ana.10136