NeuroImage
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Quantitative transverse relaxation rates in normal aging brain are essential to investigate pathologies associated with iron accumulation and tissue degeneration. Since absolute values depend on imaging methods and magnetic field strengths, continuous evaluation of specific reference values remains requisite. Multi-echo turbo spin echo and multi-echo gradient recalled echo imaging sequences were applied to 66 healthy subjects (18-84years) at 3T to quantify the irreversible (R2), effective (R2*) and reversible (R2'=R2*-R2) transverse relaxation rates. ⋯ The low intercept of R2' vs. iron content suggests a nearly sole sensitivity of R2' to iron in deep GM, potentially allowing a more specific estimation of the iron content than R2 or R2*. Since R2* and R2' depend on the fiber orientation, their feasibility to estimate iron content in WM is challenging. The analysis of R2' related to R2 may provide valuable information about the size of iron deposits.
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Randomized Controlled Trial
Gray matter and intrinsic network changes in the posterior cingulate cortex after selective serotonin reuptake inhibitor intake.
Preclinical studies have demonstrated that serotonin (5-HT) challenge changes neuronal circuitries and microarchitecture. However, evidence in human subjects is missing. Pharmacologic magnetic resonance imaging (phMRI) applying selective 5-HT reuptake inhibitors (SSRIs) and high-resolution structural and functional brain assessment is able to demonstrate the impact of 5-HT challenge on neuronal network morphology and functional activity. ⋯ Short-term administration of SSRIs changes gray matter structures, consistent with previous work reporting enhancement of neuroplasticity by serotonergic neurotransmission. Furthermore, increased gray matter in the PCC is associated with increased functional connectivity in one of the brain's metabolically most active regions. Our novel findings provide convergent evidence for dynamic alterations of brain structure and function associated with SSRI pharmacotherapy.
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Novel MR image acquisition strategies have been investigated to elicit contrast within the thalamus, but direct visualization of individual thalamic nuclei remains a challenge because of their small size and the low intrinsic contrast between adjacent nuclei. We present a step-by-step specific optimization of the 3D MPRAGE pulse sequence at 7T to visualize the intra-thalamic nuclei. We first measured T1 values within different sub-regions of the thalamus at 7T in 5 individuals. ⋯ The mean Euclidean distance between the centers of mass of MR- and Morel atlas-defined nuclei was 2.67mm (±1.02mm). The reproducibility of the MR-defined nuclei was excellent with intraclass correlation coefficient measured at 0.997 and a mean Euclidean distance between corresponding centers of mass found at first versus second readings of 0.69mm (±0.38mm). This 7T strategy paves the way to better identification of thalamic nuclei for neurosurgical planning and investigation of regional changes in neurological disorders.
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Blast-related traumatic brain injury (TBI) has been one of the "signature injuries" of the wars in Iraq and Afghanistan. However, neuroimaging studies in concussive 'mild' blast-related TBI have been challenging due to the absence of abnormalities in computed tomography or conventional magnetic resonance imaging (MRI) and the heterogeneity of the blast-related injury mechanisms. The goal of this study was to address these challenges utilizing single-subject, module-based graph theoretic analysis of resting-state functional MRI (fMRI) data. ⋯ Again, there were not substantial differences on the follow-up scans. Taken together, these results indicate that single-subject, module-based graph theoretic analysis of resting-state fMRI provides potentially useful information for concussive blast-related TBI if high quality scans can be obtained. The underlying biological mechanisms and consequences of disrupted between-module connectivity are unknown, thus further studies are required.
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Interest has recently grown in multi-center studies, which have more power than smaller studies in conducting sophisticated evaluations of basic neuroanatomy and neurodegenerative disorders. The large number of subjects that result from pooling multi-center datasets increases sensitivity, but also introduces a between-center variance component. Taking sex differences as an example, we examined the effects of different ratios of cases to controls (males to females) between scanners in multi-scanner morphometric studies, using voxel-based morphometry and data obtained on two scanners of the exact same model. ⋯ When the ratio of males to females was balanced, the inclusion of scanner as a covariate in the statistical analysis had almost no influence on the results of analyses of sex differences. When the ratio of males to females was ill-balanced, the inclusion of scanner as a covariate suppressed scanner effects on the results, but made sex differences less likely to become significant. The present results suggest that as long as the ratio of cases to controls is well-balanced across different scanners, it is not always necessary to include scanner as a covariate in the statistical analysis, and that when the ratio of cases to controls is ill-balanced across scanners, the inclusion of scanner as a covariate in the statistical analysis can suppress scanner effects, but may make differences less likely to be detected.