MRI assessment of amplitude of low-frequency fluctuation in rat brains with acute cerebral ischemic stroke.

To investigate fluctuations in the amplitude of low-frequency blood oxygenation level-dependent (BOLD) fMRI during acute brain ischemia, and to evaluate the use of amplitude of low-frequency fluctuations (ALFFs) in resting state fMRI for assessing super-acute focal cerebral ischemic stroke. A super-acute stroke model with middle cerebral artery occlusion (MCAO) in the rat was employed. Spontaneous fluctuations were recorded using a series of gradient echo-planar imaging (EPI) images before and 30 min, 60 min, 2 h, 6 h, 12 h, and 24 h after MCAO. After preprocessing, serial fMRI data were obtained by fast Fourier transformation to calculate the ALFFs. Statistical parametric mapping software was used for the statistical analysis of ALFFs. T2-weighted images and diffusion weighted images (DWI) were also performed to detect the ischemic lesion. The signal intensities of abnormal ALFFs increased and migrated from the core of the ischemic lesion areas to the edge of lesion following MCAO. The dynamic changes in the ALFF maps demonstrated that the sizes of the ALFF regions exceeded beyond the borderline of the DWI lesions during the super-acute ischemic stroke stage. There was a significant difference in the ALFFs maps between the ischemic stroke group and the control group (P<0.005; cluster size>10 voxels), which mainly occurred in the periphery of the ischemic region in the cortex. These data suggest that ALFF maps provide hemodynamic BOLD information on neural activity, and have potential for predicting survival and prognosis of acute ischemic brain tissues.