Floris Vanhevel

Prefrontal GABA concentration changes in women-Influence of menstrual cycle phase, hormonal contraceptive use, and correlation with premenstrual symptoms.

Prefrontal regions are involved in processing emotional stimuli and are a topic of interest in clinical and neurological research. Although sex steroids are potent neuromodulators, the influence of menstrual cycle phase and hormonal contraceptive use is rarely taken into account in neuroimaging studies. Our purpose was to evaluate changes in gamma-aminobutyric acid (GABA) in women, as measured by magnetic resonance spectroscopy (MRS), with phases of the menstrual cycle and use of hormonal contraceptives, and to assess correlations with premenstrual symptoms.Three MRI sessions per cycle were obtained in the natural cycle group, and two sessions in the hormonal contraceptives group. In addition to an anatomical scan, single voxel MRS in the prefrontal area was performed. After quality control, 10 women with natural cycle and 21 women taking hormonal contraceptives were included for analysis. Peripheral blood samples were obtained to determine endogenous hormone concentrations. Subjects were asked to complete a daily rating of severity of problems questionnaire, to quantify premenstrual symptoms. In the natural cycle group, we found a significant increase in prefrontal GABA concentration at the time of ovulation. Conversely, in the hormonal contraceptives group, no differences were found between the pill phase and pill-free phase. GABA concentrations did not significantly correlate with endogenous hormone levels, nor with premenstrual symptoms. Our results indicate that spectroscopically measured GABA concentrations are higher during ovulation in women with a natural menstrual cycle. We suggest that neuroimaging studies should take into account this variability.

Altered functional brain connectivity in patients with visually induced dizziness

Background Vestibular patients occasionally report aggravation or triggering of their symptoms by visual stimuli, which is called visually induced dizziness (VID). These patients therefore experience dizziness, discomfort, disorientation and postural unsteadiness. The underlying pathophysiology of VID is still poorly understood. Objective The aim of the current explorative study was to gain a first insight in the underlying neural aspects of VID. Methods We included 10 VID patients and 10 healthy matched controls, all of which underwent a resting state fMRI scan session. Changes in functional connectivity were explored by means of the intrinsic connectivity contrast (ICC). Seed-based analysis was subsequently performed in visual and vestibular seeds. Results We found a decreased functional connectivity in the right central operculum (superior temporal gyrus), as well as increased functional connectivity in the occipital pole in VID patients as compared to controls in a hypothesis-free analysis. A weaker functional connectivity between the thalamus and most of the right putamen was measured in VID patients in comparison to controls in a seed-based analysis. Furthermore, also by means of a seed-based analysis, a decreased functional connectivity between the visual associative area and the left parahippocampal gyrus was found in VID patients. Additionally, we found increased functional connectivity between thalamus and occipital and cerebellar areas in the VID patients, as well as between the associative visual cortex and both middle frontal gyrus and precuneus. Conclusions We found alterations in the visual and vestibular cortical network in VID patients that could underlie the typical VID symptoms such as a worsening of their vestibular symptoms when being exposed to challenging visual stimuli. These preliminary findings provide the first insights into the underlying functional brain connectivity in VID patients. Future studies should extend these findings by employing larger sample sizes, by investigating specific task-based paradigms in these patients and by exploring the implications for treatment.

Diffusion kurtosis imaging with free water elimination: A bayesian estimation approach: DKI With Free Water Elimination

Diffusion kurtosis imaging (DKI) is an advanced magnetic resonance imaging modality that is known to be sensitive to changes in the underlying microstructure of the brain. Image voxels in diffusion weighted images, however, are typically relatively large making them susceptible to partial volume effects, especially when part of the voxel contains cerebrospinal fluid. In this work, we introduce the “Diffusion Kurtosis Imaging with Free Water Elimination” (DKI‐FWE) model that separates the signal contributions of free water and tissue, where the latter is modeled using DKI.

Super-resolution T1 estimation: Quantitative high resolution T1 mapping from a set of low resolution T1-weighted images with different slice orientations

Quantitative T1 mapping is a magnetic resonance imaging technique that estimates the spin‐lattice relaxation time of tissues. Even though T1 mapping has a broad range of potential applications, it is not routinely used in clinical practice as accurate and precise high resolution T1 mapping requires infeasibly long acquisition times.