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Oxygenation-Sensitive Magnetic Resonance Imaging in Acute Ischemic Stroke Using T2′/R2′ Mapping: Influence of Relative Cerebral Blood Volume

Background and Purpose— Quantitative T2′/R2′ mapping detect locally increased concentrations of deoxygenated hemoglobin—causing a decrease of T2′ and increase of R2′—and might reflect increased cerebral oxygen extraction fraction. Because increases of (relative) cerebral blood volume (rCBV) may influence T2′ and R2′ through accumulation of deoxygenated hemoglobin, we aimed to investigate the impact of rCBV on T2′/R2′ in patients with ischemic stroke. Methods— Data from patients with acute internal carotid artery and middle cerebral artery occlusion were analyzed. T2′, R2′, and rCBV were measured within the ischemic core, slightly and severely hypoperfused areas, and their relationship was examined. Results— A strong negative correlation with rCBV was found for R2′ (r=−0.544; P=0.002), and T2′ correlated positively with rCBV (r=0.546; P=0.001) in time-to-peak–delayed areas. T2′/R2′ within hypoperfused tissue remained unchanged at normal or elevated rCBV levels. Conclusions— T2′ decrease/R2′ increase within hypoperfused areas in ischemic stroke is not caused by local elevations of rCBV but most probably only by increased cerebral oxygen extraction fraction. However, considering rCBV is crucial to assess extent of oxygen extraction fraction changes by means of T2′/R2′.