In Vivo Sodium MRI for Mouse Model of Ischemic Stroke at 7 T: Preliminary Results

Previous studies have used sodium magnetic resonance imaging (MRI) to investigate the increase in tissue sodium concentration that occurs during a stroke by using various animal models of brain ischemia. However, most of these studies have involved rats, cats, or nonhuman primates. Although studies involving mice are relatively scant, mice have become the principal animal model for studying many human diseases, particularly in the field of genetics. Accordingly, this study employed sodium MRI to monitor changes in the intensity of sodium signals in a mouse model of ischemic stroke. The experiments were conducted using a 7-T MRI system, and a commercial double-tuned sodium/proton transmit-receive surface coil was used to capture the sodium and proton signal images. Sodium MRI was performed using a fast low-angle shot pulse sequence. The mice underwent middle cerebral artery occlusion to induce focal brain ischemia 48 h before the MRI scans were performed. The signal intensity of the sodium image was determined for a region of interest (ROI) in the ischemic area, and an ROI contralateral to this area. The average signal intensity in the sodium images of the mouse brains exhibited a 2.51-fold increase and a standard deviation was 0.93. The results of this study demonstrate the feasibility of using a 7-T MRI system to perform sodium MRI of a mouse model of ischemic stroke. The sodium signal intensity of the mouse brain revealed a substantial increase in sodium levels in the ischemic area compared with that in the contralateral brain hemisphere.