NeuroImage
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Diffusion kurtosis as an in vivo imaging marker for reactive astrogliosis in traumatic brain injury.
Diffusion Kurtosis Imaging (DKI) provides quantifiable information on the non-Gaussian behavior of water diffusion in biological tissue. Changes in water diffusion tensor imaging (DTI) parameters and DKI parameters in several white and gray matter regions were investigated in a mild controlled cortical impact (CCI) injury rat model at both the acute (2 h) and the sub-acute (7 days) stages following injury. Mixed model ANOVA analysis revealed significant changes in temporal patterns of both DTI and DKI parameters in the cortex, hippocampus, external capsule and corpus callosum. ⋯ Monitoring changes in MK allows the investigation of molecular and morphological changes in vivo due to reactive astrogliosis and may complement information available from standard DTI parameters. To date the use of diffusion tensor imaging has been limited to study changes in white matter integrity following traumatic insults. Given the sensitivity of DKI to detect microstructural changes even in the gray matter in vivo, allows the extension of the technique to understand patho-morphological changes in the whole brain following a traumatic insult.
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There are a number of symptoms, both neurological and behavioral, associated with a single episode of r mild traumatic brain injury (mTBI). Neuropsychological testing and conventional neuroimaging techniques are not sufficiently sensitive to detect these changes, which adds to the complexity and difficulty in relating symptoms from mTBI to their underlying structural or functional deficits. With the inability of traditional brain imaging techniques to properly assess the severity of brain damage induced by mTBI, there is hope that more advanced neuroimaging applications will be more sensitive, as well as specific, in accurately assessing mTBI. ⋯ Connections between the left dorso-lateral prefrontal cortex and left lateral parietal cortex showed a significant reduction in magnitude as the number of concussions increased. Regression analysis also indicated an overall loss of connectivity as the number of mTBI episodes increased. Our findings indicate that alterations in the brain resting state default mode network in the subacute phase of injury may be of use clinically in assessing the severity of mTBI and offering some insight into the pathophysiology of the disorder.
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The thickness of the human cerebral cortex, which provides valuable information in the studies of normal and abnormal neuroanatomy, is commonly estimated using high-resolution, volumetric magnetization-prepared rapid gradient echo (MP-RAGE) magnetic resonance imaging due to its strong T1-weighted contrast and high signal-to-noise ratio. However, the accuracy of cortical thickness estimates using MP-RAGE is potentially contaminated by susceptibility-induced signal loss particularly at regions in close proximity to air-filled cavities. The purpose of this work is to investigate the feasibility of susceptibility-resistant variable-flip-angle (VFA) three-dimensional turbo/fast spin echo imaging for reliable estimation of cortical thickness of the human brain, wherein 1) radio-frequency (RF) pulse refocuses susceptibility-induced spin de-phasing, 2) the VFA refocusing pulse train is applied for a tissue-specific prescribed signal evolution along the echo train, 3) the desired T1-weighted contrast is achieved by composite restore pulses at the end of the refocusing pulse train, and 4) blood signals are suppressed using the VFA scheme combined with increasing moments of flow-sensitizing gradients while dura mater signals are attenuated due to short T2 relaxation time, which alleviates potential failure in brain segmentation. ⋯ Image processing is then performed using the Freesurfer, resulting in mean and standard deviations of cortical thickness for the entire cortical surfaces. Statistical analysis demonstrates that particularly in the inferior prefrontal and temporal regions heavily affected by susceptibility-induced signal loss conventional MP-RAGE, if compared with the proposed method, significantly under-estimates cortical thickness. It is expected that the proposed pulse sequence, which is resistant to susceptibility-induced signal loss and attenuates the signal intensity of blood and dura mater, can be a potentially promising alternative to conventional MP-RAGE in reliably estimating cortical thickness for the entire brain.
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The five-factor model organizes personality traits into five factors: Neuroticism, Extraversion, Openness to Experience, Agreeableness, and Conscientiousness. Measures of these personality traits predict people's behaviors and important outcomes of their lives. Therefore, understanding the neural correlates of these personality traits is important. ⋯ Furthermore, Neuroticism correlated positively with MD in the anterior cingulum and uncinate fasciculus, tracts interconnecting PFC and amygdala. Openness correlated negatively with MD of WM adjacent to the dorsolateral PFC in both hemispheres. These findings suggest that greater Neuroticism associates with worse integrity of WM interconnecting extensive cortical and subcortical structures including the PFC and amygdala and that greater Openness associates with better integrity of WM interconnecting extensive cortical and subcortical structures including the dorsolateral PFC.
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Magnetization transfer (MT) reflects the exchange of magnetization between protons bound to macromolecules, such as lipids and proteins, and protons in free liquid, and thus might be an early marker for subtle and undetermined pathologic changes in tissue. Detailed analysis of the entire MT phenomenon, however, commonly requires extensive data acquisition and scanning time, and hence is only of limited clinical interest. Therefore, in practice, magnetization transfer effects are commonly confined into a simple ratio measure, the so-called magnetization transfer ratio (MTR), calculated from a MT-weighted and a non-MT-weighted image. ⋯ Structures with highly similar MTR-values, such as the crus cerebri and the anterior commissure in the WM, or the pallidum and the amygdala in the GM, however, were also found that showed significant differences in most quantitative parameters. This observation was confirmed from simulations revealing that the overall effect on MTR from an increase (decrease) in relaxation times may be counterbalanced with a decrease (increase) in MT parameters. These findings corroborate the expectation that qMT is superior to MTR imaging, especially for the evaluation and assessment of pathologic or physiological changes in healthy and pathologic brain tissue.