Evaluation of Recanalization of Occluded Middle Cerebral Artery and Restored Cerebral Blood Flow in Rats with Transient Brain Ischemia: A Combination Study of Digital Subtraction Angiography and ¹⁵O-water Positron Emission Tomography

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The purpose of this study was to validate the usefulness of digital subtraction angiography (DSA) using the fluoroscopic mode of a small-animal PET/CT in detecting recanalization of occluded middle cerebral artery (MCA), and to evaluate reperfusion by ¹⁵O-water positron emission tomography (PET) in rats with transient unilateral occlusion of MCA. Methods: Rats with (n=6) and without transient unilateral MCA occlusion (n=6) were examined. DSA was performed in the X-ray fluoroscopic mode with small-animal PET/CT. An iodine contrast medium (0.3 mL) was administered by bolus injection via the catheter in the internal carotid artery under isoflurane anesthesia. A 10-min dynamic PET scanning was started simultaneously with an intravenous bolus injection of ¹⁵O-water during MCA occlusion (occlusion duration: 45 min) and approximately 30 min after recanalization in ischemic rats. Cerebral blood flow (CBF) was evaluated semi-quantitatively as CBF index determined from the ¹⁵O-water PET images, which is normalized to the injected dose per body weight. Results: DSA revealed recanalization of the ipsilateral MCA in the ischemic rat models. The ¹⁵O-water PET images showed decreased CBF during MCA occlusion and recovery of the CBF after recanalization in the ipsilateral MCA territory. The CBF index of the ipsilateral and contralateral MCA territories during MCA occlusion were 0.84±0.12 and 1.66±0.13, respectively, and those after recanalization were 1.24±0.17 and 1.67±0.10, respectively. The CBF index of the ipsilateral MCA territory increased significantly after recanalization (p=0.04), although it remained significantly lower than the CBF index of the contralateral MCA territory (p=0.04). Conclusions: This study demonstrated the feasibility of DSA using the X-ray fluoroscopic mode of a small-animal PET/CT. Recovery of the CBF was not sufficient at 30 min after recanalization in rats with transient MCA occlusion.