Objective To estimate the maximium diagnostic efficiency of small coverage CT brain perfusion.Methods Twenty-two patients with acute ischemic cerebral stroke,enrolled in this retrospective study,underwent perfusion CT scanning and CT perfusion imaging 1-24 h after onset of the disease.Cerebral infarction core area and penumbra volume of perfusion CT were measured with the 80 mm Z-axis coverage CT perfucion parameters.The penumbra/penumbra+infarction core area ratio was calculated.The sensitivity and specificity of small coverage CT brain perfusion were calculated with the treatment plan worked out according to the 80 mm Z-axis coverage CT brain perfucion as the baseline.Results Forty milimeter Z-axis coverage CT brain perfusion could show the accurate infarction core area and penumbra volume when the penumbra/penumbra+infarction core area ratio was0.2.Conclusion Forty mm Z-axis coverage CT brain perfusion can show the area and nature of infarction in patients with acute middle cerebral stroke when the penumbra /penumbra+infarction core area ratio is0.2.