Perfusion measurements of the brain: using dynamic CT for the quantitativeassessment of cerebral ischemia in acute stroke

Objective: Perfusion CT has been successfully used as a functional imaging technique for the differential diagnosis of patients with hyperacute stroke . We investigated to what extent this technique can also be used for the qu antitative assessment of cerebral ischemia. Methods and material: We studie d linearity, spatial resolution and noise behaviour of cerebral blood flow (CBF) determination with computer simulations and phantom measurements. Sta tistical ROI based analysis of CBF images of a subset of 38 patients from a controlled clinical stroke study with currently more than 75 patients was done to check the power of relative cerebral blood flow (rCBF) values to pr edict definite infarction and ischemic penumbra. Classification was perform ed using follow-up CT and MR data. Results: Absolute CBF values were system atically underestimated, the degree depended on the cardiac output of the p atients. Phantom measurements and simulations indicated very good linearity allowing reliable calculation of rCBF values. Infarct and penumbra areas i n 19 patients receiving standard heparin therapy had mean rCBF values of 0. 19 and 0.62, respectively. The corresponding values for 19 patients receivi ng local intraarterial fibrinolysis were 0.18 and 0.57. The difference betw een infarct and penumbra values was highly significant (P < 0.0001) in both groups. No penumbra area was found with an rCBF value of less than 0.20. W hile in the heparin group only 25% of all areas with an rCBF between 0.20 a nd 0.35 survived, in the fibrinolytic group 61% of these areas could be sav ed (P < 0.05). Conclusion: Perfusion CT is a fast and practical technique f or routine clinical application. It provides substantial and important addi tional information for the selection of the optimal treatment strategy for patients with hyperacute stroke. Relative values of cerebral blood flow dis criminate very well between areas of reversible and irreversible ischemia; an rCBF value of 0.20 appears to be a definite lower limit for brain tissue to survive an ischemic injury. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.