Quantitative Assessment of the Balance between Oxygen Delivery and Consumption in the Rat Brain after Transient Ischemia with T2-BOLD Magnetic Resonance Imaging

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Abstract
The balance between oxygen consumption and delivery in the rat brain after exposure to transient ischemia was quantitatively studied with single-spin echo T2-BOLD (blood oxygenation level–dependent) magnetic resonance imaging at 4.7 T. The rats were exposed to graded common carotid artery occlusions using a modification of the four-vessel model of Pulsinelli. T2, diffusion, and cerebral blood volume were quantified with magnetic resonance imaging, and CBF was measured with the hydrogen clearance method. A transient common carotid artery occlusion below the CBF value of approximately 20 mL·100 g−1·min−1 was needed to yield a T2 increase of 4.6 ± 1.2 milliseconds (approximately 9% of cerebral T2) and 6.8 ± 1.7 milliseconds (approximately 13% of cerebral T2) after 7 and 15 minutes of ischemia, respectively. Increases in CBF of 103 ± 75% and in cerebral blood volume of 29 ± 20% were detected in the reperfusion phase. These hemodynamic changes alone could account for only approximately one third of the T2 increase in luxury perfusion, suggesting that a substantial increase in blood oxygen saturation (resulting from reduced oxygen extraction by the brain) is needed to explain the magnetic resonance imaging observation.

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