Combination of a Mean Transit Time Measurement with an Acetazolamide Test Increases Predictive Power to Identify Elevated Oxygen Extraction Fraction in Occlusive Carotid Artery Diseases

Reduced cerebral blood flow and cerebrovascular reactivity to acetazolamide have been used as predictors for subsequent ischemic stroke in patients with occlusive carotid artery diseases, called type 3 ischemia. However, recent studies have shown that reduced cerebrovascular reactivity to acetazolamide does not always represent elevated oxygen extraction fraction (OEF). The aim of this study was to establish the methodology to improve the validity of an acetazolamide test identifying elevated OEF. Methods: This study included 65 patients who developed transient ischemic attack or minor completed stroke attributable to occlusive carotid artery diseases. Hemodynamic and metabolic parameters in the bilateral middle cerebral artery territories were determined in all patients by O-15-gas PET. Results: Type 3 ischemia alone had 100% sensitivity and 83.2% specificity for identifying elevated OEF, but its positive predictive value and accuracy were low, 47.2% and 0.85, respectively. However, type 3 ischemia and delayed mean transit time combined had an 83.3% positive predictive value and 0.96 accuracy. Conclusion: The results strongly suggest that type 3 ischemia and delayed mean transit time together may be powerful predictors in identifying elevated OEF with high sensitivity and specificity, predictive values, and accuracy. SPECT may be able to define the patients with elevated OEF more easily and at lower costs than PET, although further study would be necessary to compare the results by using SPECT.