Browsing by Author "Nunes, Rita G."
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- Alterations of white matter microstructure in migraine patients vary in the peri-ictal phasesPublication . Fouto, Ana R.; Nunes, Rita G.; Guadilla, Irene; Ruiz-Tagle, Amparo; Esteves, Inês; Caetano, Gina; Silva, Nuno A.; Vilela, Pedro; Gil-Gouveia, Raquel; Figueiredo, PatriciaAlterations in white matter (WM) microstructure are commonly found in migraine patients. Here, we employ a longitudinal study of episodic migraine without aura using diffusion magnetic resonance imaging (dMRI) to investigate whether such WM microstructure alterations vary through the different phases of the pain cycle. Fourteen patients with episodic migraine without aura related with menstruation were scanned through four phases of their (spontaneous) migraine cycle (interictal, preictal, ictal, and postictal). Fifteen healthy controls were studied in the corresponding phases of the menstrual cycle. Multishell dMRI data were acquired and preprocessed to obtain maps of diffusion parameters reflecting WM microstructure. After a whole-brain analysis comparing patients with controls, a region-of-interest analysis was performed to determine whether the patients’ microstructural changes varied across the migraine cycle in specific WM tracts. Compared with controls, patients showed reduced axial diffusivity (AD) in several WM tracts across the whole brain in the interictal phase and increased fractional anisotropy (FA) in commissural fibers in the ictal phase. Interestingly, AD returned to baseline levels during peri-ictal phases in specific projection and association fibers. In contrast, FA values decreased in the ictal phase away from normal values in a few commissural and projection tracts. Widespread WM fiber tracts suffer structural variations across the migraine cycle, suggesting microstructural changes potentially associated with limbic and salience functional networks and highlighting the importance of the cycle phase in imaging studies of migraine.
- Impact of susceptibility-induced distortion correction on perfusion imaging by pCASL with a segmented 3D GRASE readoutPublication . Domingos, Catarina; Fouto, Ana R.; Nunes, Rita G.; Ruiz-Tagle, Amparo; Esteves, Inês; Silva, Nuno A.; Vilela, Pedro; Gil-Gouveia, Raquel; Figueiredo, PatríciaPurpose: The consensus for the clinical implementation of arterial spin labeling (ASL) perfusion imaging recommends a segmented 3D Gradient and Spin-Echo (GRASE) readout for optimal signal-to-noise-ratio (SNR). The correction of the associated susceptibility-induced geometric distortions has been shown to improve diagnostic precision, but its impact on ASL data has not been systematically assessed and it is not consistently part of pre-processing pipelines. Here, we investigate the effects of susceptibility-induced distortion correction on perfusion imaging by pseudo-continuous ASL (pCASL) with a segmented 3D GRASE readout. Methods: Data acquired from 28 women using pCASL with 3D GRASE at 3T was analyzed using three pre-processing options: without distortion correction, with distortion correction, and with spatial smoothing (without distortion correction) matched to control for blurring effects induced by distortion correction. Maps of temporal SNR (tSNR) and relative perfusion were analyzed in eight regions-of-interest (ROIs) across the brain. Results: Distortion correction significantly affected tSNR and relative perfusion across the brain. Increases in tSNR were like those produced by matched spatial smoothing in most ROIs, indicating that they were likely due to blurring effects. However, that was not the case in the frontal and temporal lobes, where we also found increased relative perfusion with distortion correction even compared with matched spatial smoothing. These effects were found in both controls and patients, with no interactions with the participant group. Conclusion: Correction of susceptibility-induced distortions significantly impacts ASL perfusion imaging using a segmented 3D GRASE readout, and this step should therefore be considered in ASL pre-processing pipelines. This is of special importance in clinical studies, reporting perfusion across ROIs defined on relatively undistorted images and when conducting group analyses requiring the alignment of images across different subjects.
- Impact of truncating diffusion MRI scans on diffusional kurtosis imagingPublication . Fouto, Ana R.; Henriques, Rafael N.; Golub, Marc; Freitas, Andreia C.; Ruiz-Tagle, Amparo; Esteves, Inês; Gil-Gouveia, Raquel; Silva, Nuno A.; Vilela, Pedro; Figueiredo, Patrícia; Nunes, Rita G.Objective Difusional kurtosis imaging (DKI) extends difusion tensor imaging (DTI), characterizing non-Gaussian difusion efects but requires longer acquisition times. To ensure the robustness of DKI parameters, data acquisition ordering should be optimized allowing for scan interruptions or shortening. Three methodologies were used to examine how reduced difusion MRI scans impact DKI histogram-metrics: 1) the electrostatic repulsion model (OptEEM); 2) spherical codes (OptSC); 3) random (RandomTRUNC). Materials and methods Pre-acquired difusion multi-shell data from 14 female healthy volunteers (29±5 years) were used to generate reordered data. For each strategy, subsets containing diferent amounts of the full dataset were generated. The subsampling efects were assessed on histogram-based DKI metrics from tract-based spatial statistics (TBSS) skeletonized maps. To evaluate each subsampling method on simulated data at diferent SNRs and the infuence of subsampling on in vivo data, we used a 3-way and 2-way repeated measures ANOVA, respectively. Results Simulations showed that subsampling had diferent efects depending on DKI parameter, with fractional anisotropy the most stable (up to 5% error) and radial kurtosis the least stable (up to 26% error). RandomTRUNC performed the worst while the others showed comparable results. Furthermore, the impact of subsampling varied across distinct histogram characteristics, the peak value the least afected (OptEEM: up to 5% error; OptSC: up to 7% error) and peak height (OptEEM: up to 8% error; OptSC: up to 11% error) the most afected. Conclusion The impact of truncation depends on specifc histogram-based DKI metrics. The use of a strategy for optimizing the acquisition order is advisable to improve DKI robustness to exam interruptions.
- Involvement of the cerebellum in structural connectivity enhancement in episodic migrainePublication . Matoso, Ana; Fouto, Ana R.; Esteves, Inês; Ruiz-Tagle, Amparo; Caetano, Gina; Silva, Nuno A. da; Vilela, Pedro; Gil-Gouveia, Raquel; Nunes, Rita G.; Figueiredo, PatríciaBackground: The pathophysiology of migraine remains poorly understood, yet a growing number of studies have shown structural connectivity disruptions across large-scale brain networks. Although both structural and functional changes have been found in the cerebellum of migraine patients, the cerebellum has barely been assessed in previous structural connectivity studies of migraine. Our objective is to investigate the structural connectivity of the entire brain, including the cerebellum, in individuals diagnosed with episodic migraine without aura during the interictal phase, compared with healthy controls. Methods: To that end, 14 migraine patients and 15 healthy controls were recruited (all female), and diffusion-weighted and T1-weighted MRI data were acquired. The structural connectome was estimated for each participant based on two different whole-brain parcellations, including cortical and subcortical regions as well as the cerebellum. The structural connectivity patterns, as well as global and local graph theory metrics, were compared between patients and controls, for each of the two parcellations, using network-based statistics and a generalized linear model (GLM), respectively. We also compared the number of connectome streamlines within specific white matter tracts using a GLM. Results: We found increased structural connectivity in migraine patients relative to healthy controls with a distinct involvement of cerebellar regions, using both parcellations. Specifically, the node degree of the posterior lobe of the cerebellum was greater in patients than in controls and patients presented a higher number of streamlines within the anterior limb of the internal capsule. Moreover, the connectomes of patients exhibited greater global efficiency and shorter characteristic path length, which correlated with the age onset of migraine. Conclusions: A distinctive pattern of heightened structural connectivity and enhanced global efficiency in migraine patients compared to controls was identified, which distinctively involves the cerebellum. These findings provide evidence for increased integration within structural brain networks in migraine and underscore the significance of the cerebellum in migraine pathophysiology.
- Uncovering longitudinal changes in the brain functional connectome along the migraine cycle: a multilevel clinical connectome fingerprinting frameworkPublication . Esteves, Inês; Fouto, Ana R.; Ruiz-Tagle, Amparo; Caetano, Gina; Nunes, Rita G.; Silva, Nuno A. da; Vilela, Pedro; Martins, Isabel Pavão; Gil-Gouveia, Raquel; Caballero-Gaudes, César; Figueiredo, PatríciaChanges in large-scale brain networks have been reported in migraine patients, but it remains unclear how these manifest in the various phases of the migraine cycle. Case-control fMRI studies spanning the entire migraine cycle are lacking, precluding a complete assessment of brain functional connectivity in migraine. Such studies are essential for understanding the inherent changes in the brain of migraine patients as well as transient changes along the cycle. Here, we leverage the concept of functional connectome (FC) fingerprinting, whereby individual subjects may be identified based on their FC, to investigate changes in FC and its stability across different phases of the migraine cycle.
- White matter alterations in episodic migraine without aura patients assessed with diffusion MRI: effect of free water correctionPublication . Guadilla, Irene; Fouto, Ana R.; Ruiz-Tagle, Amparo; Esteves, Inês; Caetano, Gina; Silva, Nuno A.; Vilela, Pedro; Gil-Gouveia, Raquel; Aja-Fernández, Santiago; Figueiredo, Patrícia; Nunes, Rita G.Objective To assess the efect of modeling free water (FW) on the identifcation of white matter (WM) microstructure alterations using difusion Magnetic Resonance Imaging (dMRI) in episodic migraine without aura patients compared with healthy controls. Background Difusion tensor imaging (DTI) studies examining WM in migraine patients previously overlooked the potential infuence of FW partial volume efects. Correcting FW efects could ofer a clearer understanding of WM changes in migraine. This study is the frst to incorporate FW efects when evaluating alterations in WM tracts in migraine patients, ofering a comparison to standard DTI analysis. Methods A group of 14 patients with low-frequency episodic menstrual-related migraine without aura and 15 healthy controls matched for the phase of the menstrual cycle were recruited and underwent dMRI acquisitions. FW partial volume fraction was estimated, the difusion signal corrected and the difusion parameters calculated from both FW-corrected and uncorrected signals. Tract-Based Spatial Statistics (TBSS) and WM skeleton regions of interest (ROI) analyses were used to compare between groups. Results Comparisons between control subjects and migraine patients with TBSS and ROI analyses revealed signifcantly lower axial difusivity (AD), both with and without FW correction, as well as altered FW values in migraine patients in some WM tracts. TBSS detected MD changes only after FW correction. Conclusions These fndings suggest WM alterations in these migraine patients in comparison with control subjects, in accordance with other migraine studies. Diferences in the difusion parameters might point to infammatory processes in migraine related to cellular swelling.