Arterial spin-labeling magnetic resonance imaging of brain maturation in early childhood: Mathematical model fitting to assess age-dependent change of cerebral blood flow.

PURPOSE: To determine the trajectory of age-dependent cerebral blood flow (CBF) change in infants and young children by fitting mathematical models to the imaging data. METHODS: In this retrospective study, we reviewed the arterial spin-labeling imaging studies of 49 typically developing infants and young children at postmenstrual age (PMA) ranging from 38 to 194 weeks. All patients had normal structural MR imaging. Coregistration and gray matter segmentation were performed to extract whole-brain CBF values. Regional CBF values were obtained using manual region-of-interest placement. Curve estimation regression procedures with the corrected Akaike information criterion (AICc) were performed to determine the mathematical model best fitting the relationship between the CBF (whole-brain and regional measurements) and PMA of the patients. RESULTS: Whole-brain CBF trajectory was best fitted by a cubic model (AICc = 215.95; R2 = 0.566; P < .001). Whole-brain CBF at 1, 6, 12, and 24 months was estimated to be 36, 52, 58, and 55 mL/100 g/min, respectively. Regional CBF trajectory was also best fitted by a cubic model in the frontal (AICc = 233.63; R2 = 0.442; P < .001), parietal (AICc = 229.18; R2 = 0.614; P < .001), basal ganglion (AICc = 239.39; R2 = 0.178; P = .043), temporal (AICc = 236.01; R2 = 0.441; P < .001), and occipital (AICc = 236.46; R2 = 0.475; P < .001) regions. CONCLUSIONS: In early childhood, the trajectory of CBF change was nonlinear and best fitted by the cubic model for the whole brain and all brain regions.

Tract-based spatial statistics: application to mild cognitive impairment.

RATIONALE AND OBJECTIVES: The primary objective of the current investigation was to characterize white matter integrity in different subtypes of mild cognitive impairment (MCI) using tract-based spatial statistics of diffusion tensor imaging. MATERIALS AND METHODS: The study participants were divided into 4 groups of 30 subjects each as follows: cognitively healthy controls, amnestic MCI, dysexecutive MCI, and Alzheimer's disease (AD). All subjects underwent a comprehensive neuropsychological assessment, apolipoprotein E genotyping, and 3-tesla MRI. The diffusion tensor was reconstructed and then analyzed using tract-based spatial statistics. The changes in brain white matter tracts were also examined according to the apolipoprotein E ε 4 status. RESULTS: Compared with controls, amnestic MCI patients showed significant differences in the cerebral white matter, where changes were consistently detectable in the frontal and parietal lobes. We found a moderate impact of the apolipoprotein E ε 4 status on the extent of white matter disruption in the amnestic MCI group. Patients with AD exhibited similar but more extensive alterations, while no significant changes were observed in dysexecutive MCI patients. CONCLUSION: The results from this study indicate that amnestic MCI is the most likely precursor to AD as both conditions share significant white matter damage. By contrast, dysexecutive MCI seems to be characterized by a distinct pathogenesis.

Sex dimorphism of cortical water diffusion in normal aging measured by magnetic resonance imaging.

BACKGROUND: The purpose of this study was to examine sex dimorphism in water diffusion in the brain throughout the normal aging process by magnetic resonance imaging. METHODS: Diffusion-weighted images covering the majority of the brain were acquired from 77 healthy participants. Both the mean water diffusivity and diffusion kurtosis were calculated from the cortical regions and parcellated according to the template in anatomical automatic labeling. The mean water diffusivity and diffusion kurtosis from both sexes were examined and subsequently correlated with age. Statistical significance was set at a threshold of p < 0.01 after correction for multiple comparisons. In regions that reached statistical significance, a linear regression model was performed. Analysis of variance was conducted to determine the interaction between aging and sex. RESULTS: Sex differences were observed for three aspects. First, compared to females, males presented increased mean water diffusivity and a decreased diffusion kurtosis in the frontal and temporal lobes. Second, a widespread age-related increase in mean water diffusivity was observed, which was more significant in the frontal, occipital, and temporal areas and in the cingulum in females. Third, the diffusion kurtosis decreased with aging but only in restricted areas for both sexes. For the interaction of aging and sex, the most significant change was observed with regards to mean diffusivity, mostly in the right amygdala. CONCLUSIONS: A sex-related dimorphism in water diffusion throughout the aging process was observed in the cortex using magnetic resonance imaging.