Purpose The aim of this study was to discuss the advantages of GQI reconstruction in the imaging of nerve fibers at crossing regions. Compared with DTI, the paper also discussed the advantages of GQI in imaging principles. Methods 3-T MRI data from five normal participants were reconstructed using GQI and DTI. After adjusting the parameters, we compared the differences in reconstructed nerve fibers at the crossing regions between the two methods. To complete this study, we chose four obvious examples (the optic nerve, the Superior cerebellar peduncles, the intersection of the pyramidal tract, the corpus callosum and the arcuate fibers and the intersection of the supplementary motor area (SMA) and the anterior part of arcuate fasciculus) to illustrate. Results By reconstructing nerve fibers in three regions, we can find that crossing-area images of nerve fibers significantly differed between DTI and GQI reconstruction. Although crossing fibers could be clearly and completely visualized after GQI reconstruction, they showed artifacts, incompleteness, deletions, and fractures after DTI reconstruction. After GQI reconstruction, we can find that there were two or more nerve fibers in each voxel. However, only one nerve fiber was present in each voxel after DTI reconstruction. Conclusion The imaging of crossing fibers is more complete, consistent, and accurate when they are reconstructed by GQI than when they are reconstructed by DTI.

Chronic stress is a known risk factor for both endothelial dysfunction and cardiovascular disease (CVD), but less is known of how acute mental stress affects the vasculature. In this systematic review and meta-analysis, we analyzed the impact of acute mental stress on flow-mediated dilation (FMD), an indicator of endothelial function. We searched the Medline, Cochrane, EMBASE, and ISI Web of Knowledge databases through May 2014, to identify publications in English-language journals. The primary outcome was the change in FMD from baseline to the time of measurement. We also assessed the risk of bias and the heterogeneity of included studies. Our search identified eight prospective studies, which displayed significant heterogeneity. Four studies measured FMD while the subject was performing the task; six measured FMD after the task had been completed. The total number of participants was 164. The pooled results indicate that FMD did not change significantly while the task was being performed (pooled difference in means: -0.853; 95 % confidence interval (CI), -3.926/2.220; P = 0.586); however, FMD measured after the task was completed was significantly less than baseline (pooled difference in means: -2.450; 95 %CI, -3.925/-0.975; P = 0.001). In conclusions, our findings provide evidence that an acute stressful experience has a delayed, negative impact on the function of the endothelium. Repeated exposure to short-term stress may lead to permanent injury of the vasculature. Therefore, assessment of patients' exposure to both repeated acute mental stress and chronic stress may be useful in determining their risk of developing CVD.

The existence of the superior fronto-occipital fasciculus (SFOF) in the human brain remains controversial. The aim of the present study was to clarify the existence, course, and terminations of the SFOF. High angular diffusion spectrum imaging (DSI) analysis was performed on six healthy adults and on a template of 842 subjects from the Human Connectome Project. To verify tractography results, we performed fiber microdissections of four post-mortem human brains. Based on DSI tractography, we reconstructed the SFOF in the subjects and the template from the Human Connectome Project that originated from the rostral and medial parts of the superior and middle frontal gyri. By tractography, we found that the fibers formed a compact fascicle at the level of the anterior horn of the lateral ventricle coursing above the head of caudate nucleus, medial to the corona radiate and under the corpus callosum (CC), and terminated at the parietal region via the lower part of the caudate nucleus. We consider that this fiber bundle observed by tractography is the SFOF, although it terminates mainly at the parietal region, rather than occipital lobe. By contrast, we were unable to identify a fiber bundle corresponding to the SFOF in our fiber dissection study. Although we did not provide definite evidence of the SFOF in the human brain, these findings may be useful for future studies in this field.