Display omitted
•Gradient inhomogeneity causes deviation of the measured fibers direction.•The deviation depends on the position fibers position inside the scanner.•The errors are systematic, so they ...cannot be mitigated by increasing SNR.•BSD-DTI method has the potential to improve the tractography fidelity.
The DTI-based tractography, despite its restrictions, is the most widely utilized fiber tracking method in clinical practice. Its fidelity is strictly dependent on the precision and accuracy of the DTI measurement, which in turn is limited by the linearity of the diffusion sensitizing gradient.
The influence of the gradient distortions on the differences between the real and measured orientation of fibers was investigated by computer simulations. In addition, the potential of the b-matrix Spatial Distribution in DTI (BSD-DTI) technique in correcting such kind of errors was demonstrated experimentally.
The simulations revealed that the diffusion gradient inhomogeneity, if not corrected, leads to the erroneous indication of the fiber direction. The average and maximum deviations were about 1° and 15°, respectively. Remarkably, the deviation between the real and measured orientation of fibers is directionally dependent, what was confirmed in MRI measurement. The deviation errors can be effectively corrected by preceding the DTI measurement with the BSD-DTI calibration.
Objectives SARS-CoV-2 infection is associated with a decline in functional outcomes; many patients experience persistent symptoms, while the underlying pathophysiology remains unclear. This study ...investigated white matter (WM) integrity on brain MRI in hospitalized COVID-19 patients and its associations with clinical outcomes, including long COVID. Materials and methods We included hospitalized COVID-19 patients and controls from CORONavirus and Ischemic Stroke (CORONIS), an observational cohort study, who underwent MRI-DWI imaging at baseline shortly after discharge (<3 months after positive PCR) and 3 months after baseline scanning. We assessed WM integrity using diffusion tensor imaging (DTI) and neurite orientation dispersion and density imaging (NODDI) and performed comparisons between groups and within patients. Clinical assessment was conducted at 3 and 12 months with functional outcomes such as modified Rankin Scale (mRS), Post-COVID-19 Functional Status scale (PCFS), Visual Analogue Scale (VAS), and long COVID, cognitive assessment was conducted by the Modified Telephone Interview for Cognitive Status (TICS-M), and the Hospital Anxiety and Depression Scale (HADS) was used to assess mood disorder. Associations between WM integrity and clinical outcomes were evaluated using logistic regression and linear regression. Results A total of 49 patients (mean age 59.5 years) showed higher overall peak width of skeletonized mean diffusivity (PSMD) ( p = 0.030) and lower neurite density index (NDI) in several WM regions compared with 25 controls at the baseline ( p < 0.05; FWE-corrected) but did not remain statistically significant after adjusting for WM hyperintensities. Orientation dispersion index (ODI) increased after 3-month follow-up in several WM regions within patients ( p < 0.05), which remained significant after correction for changes in WMH volume. Patients exhibited worse clinical outcomes compared with controls. Low NDI at baseline was associated with worse performance on the Post-COVID-19 Functional Status scale after 12 months ( p = 0.018). Conclusion After adjusting for WMH, hospitalized COVID-19 patients no longer exhibited lower WM integrity compared with controls. WM integrity was generally not associated with clinical assessments as measured shortly after discharge, suggesting that factors other than underlying WM integrity play a role in worse clinical outcomes or long COVID.
The human brain is organized into large-scale functional modules that have been shown to evolve in childhood and adolescence. However, it remains unknown whether the underlying white matter ...architecture is similarly refined during development, potentially allowing for improvements in executive function. In a sample of 882 participants (ages 8–22) who underwent diffusion imaging as part of the Philadelphia Neurodevelopmental Cohort, we demonstrate that structural network modules become more segregated with age, with weaker connections between modules and stronger connections within modules. Evolving modular topology facilitates global network efficiency and is driven by age-related strengthening of hub edges present both within and between modules. Critically, both modular segregation and network efficiency are associated with enhanced executive performance and mediate the improvement of executive functioning with age. Together, results delineate a process of structural network maturation that supports executive function in youth.
Display omitted
•Structural brain modules become more segregated during youth•Targeted strengthening of hub edges simultaneously promotes network efficiency•Enhanced modular segregation mediates improvements in executive function in youth
Baum et al. apply network analytic techniques to demonstrate that human white matter networks become increasingly modular during adolescent development. Furthermore, targeted strengthening of hub connections facilitates global network integration. This process of network evolution mediates improvements in executive functioning during youth.
Schizophrenia is associated with chronic subclinical inflammation and decreased integrity of the corpus callosum (CC). Our previous study showed associations between peripheral IL-6 levels and the ...integrity of the CC. Epigenetic studies show associations between methylation of the genes related to immunological processes and integrity of the CC.
To investigate correlations between methylation status of IL-6 promotor and peripheral IL-6 levels and the integrity of the CC in schizophrenia.
The participants were 29 chronic schizophrenia patients (SCH) and 29 controls. Decreased integrity of the CC was understood as increased mean diffusivity (MD) and/or decreased fractional anisotropy (FA) in diffusion tensor imaging. Peripheral IL-6 concentrations were measured in serum samples and IL-6 promoter methylation status of 6 CpG sites was analyzed in peripheral leukocytes by pyrosequencing.
Moderate positive correlations were found between CpG1 methylation and the MD of proximal regions of the CC (CCR1–CCR3) and between CpGmean and MD of CCR1 in SCH. Weaker positive correlations were found for CpGmean with CCR2 and CCR3 and negative correlations were found for CpG1 and FA of CCR3 in SCH. Multivariate regression showed that methylation of CpG1, type of antipsychotic treatment, and their interaction were significant independent predictors of MD of CCR1 in SCH. Methylation of CpG2 was negatively correlated with serum IL-6 in SCH.
The methylation level of the IL-6 promotor region in peripheral leukocytes is associated with the integrity of the CC in schizophrenia and this association may depend on the type of antipsychotic treatment. Further studies are necessary to explain the mechanisms of the observed associations.
Various diffusion MRI (dMRI) preprocessing pipelines are currently available to yield more accurate diffusion parameters. Here, we evaluated accuracy and robustness of the optimized Diffusion ...parameter EStImation with Gibbs and NoisE Removal (DESIGNER) pipeline in a large clinical dMRI dataset and using ground-truth phantoms. DESIGNER, a preprocessing pipeline targeting various imaging artifacts in diffusion MRI data, has been modified to improve denoising and target Gibbs ringing for partial Fourier acquisitions. We compared the revised DESIGNER (Dv2) (including denoising, Gibbs removal, correction for motion, echo planar imaging (EPI) distortion, and eddy currents) against the original DESIGNER (Dv1) pipeline, minimal preprocessing (including correction for motion, EPI distortion, and eddy currents only), and no preprocessing on a large clinical dMRI dataset of 524 control subjects with ages between 25 and 75 years old. We evaluated the effect of specific processing steps on age correlations in white matter with diffusion tensor imaging (DTI) and diffusion kurtosis imaging (DKI) metrics. We also evaluated the added effect of minimal Gaussian smoothing to deal with noise and to reduce outliers in parameter maps compared to DESIGNER-v2’s noise removal method. Moreover, Dv2’s updated noise and Gibbs removal methods were assessed using a ground truth dMRI phantom to evaluate accuracy. Results show age correlations of DTI and DKI metrics in white matter were affected by the preprocessing pipeline, causing systematic differences in absolute parameter values and loss or gain of statistical significance. Both in clinical dMRI and ground-truth phantoms, Dv2 pipeline resulted in the smallest number of outlier voxels and improved accuracy in DTI and DKI metrics as noise was reduced and Gibbs removal was improved. Thus, DESIGNER-v2 provides more accurate and robust DTI and DKI parameter maps by targeting common artifacts present in dMRI data acquired in clinical settings, as compared to no preprocessing or minimal preprocessing.
Introduction
Schizophrenia is a chronic mental illness with unclear etiology. It is characterized by symptoms in various psychopathological domains (e.g. positive, negative). One of the concepts ...explaining the etiology of schizophrenia is the disconnection hypothesis. It assumes the existence of structural and functional disorders within the connections of brain regions. White matter is largely responsible for the quality of these connections. One of the important structures of white matter is the superior longitudinal fascicle (SLF) which connects many cortical structures.
Objectives
The main aim of our study was to search for a relationship between the integrity of SLF and various psychopathological dimensions among schizophrenia patients.
Methods
42 schizophrenia subjects (SS) and 32 healthy controls (HC) participated in the study. All study participants underwent DTI-MRI analysis. The psychopathology of SS was assessed using the Positive and Negative Syndrome Scale (PANSS). In the study, we used the PANSS dimensions proposed by Shafer. Then, the SLF analysis was performed using fractional anisotropy (FA) and mean diffusivity (MD) parameters.
Results
The differences in FA and MD values in SLF bilaterally between groups were confirmed. A correlation was found between MD values in left SLF and positive symptoms (p = 0.040) and excitement (p = 0.012). A correlation was found between the MD values in the right SLF and the symptoms of disorganization (p <0.000) and excitement (p = 0.004).
Conclusions
SLF seems to play a role in the etiopathogenesis of schizophrenia. Disturbed SLF integrity may be involved in the development of positive, disorganization and excitement symptoms.
Disclosure
No significant relationships.
Diffusion tensor imaging (DTI) is a well-established magnetic resonance imaging (MRI) technique used for studying microstructural changes in the white matter. As with many other imaging modalities, ...DTI images suffer from technical between-scanner variation that hinders comparisons of images across imaging sites, scanners and over time. Using fractional anisotropy (FA) and mean diffusivity (MD) maps of 205 healthy participants acquired on two different scanners, we show that the DTI measurements are highly site-specific, highlighting the need of correcting for site effects before performing downstream statistical analyses. We first show evidence that combining DTI data from multiple sites, without harmonization, may be counter-productive and negatively impacts the inference. Then, we propose and compare several harmonization approaches for DTI data, and show that ComBat, a popular batch-effect correction tool used in genomics, performs best at modeling and removing the unwanted inter-site variability in FA and MD maps. Using age as a biological phenotype of interest, we show that ComBat both preserves biological variability and removes the unwanted variation introduced by site. Finally, we assess the different harmonization methods in the presence of different levels of confounding between site and age, in addition to test robustness to small sample size studies.
•Significant site and scanner effects exist in DTI scalar maps.•Several multi-site harmonization methods are proposed.•ComBat performs the best at removing site effects in FA and MD.•Voxels associated with age in FA and MD are more replicable after ComBat.•ComBat is generalizable to other imaging modalities.
Background. Multiple sclerosis (MS) is an autoimmune disease that targets the central nervous system (CNS). A patient’s degree of demyelination and axonal degeneration can only be roughly estimated ...based on clinical symptoms, neurochemical analysis or standard clinical MRI. Magnetic resonance diffusion tensor imaging (DTI) may provide more information on MS pathology than T1- and T2-weighted MRI alone. Glial fibrillary acidic protein (GFAP) uniquely found in astrocytes in the (CNS), non-myelinating Schwann cells in the peripheral nervous system (PNS), and enteric glial cells. GFAP is postulated to be a biomarker of astrocytic damage and reactive astrogliosis. Methods. A total of 60 patients with MS was categorized into three equal groups according to The Multiple Sclerosis Progression Discussion Tool (MSProDiscuss tool): RRMS, SPMS, RRMS with high risk to become SPMS and 20 healthy controls. Baseline clinical characteristics and detailed medical and neurological history were taken into consideration, as well as time of onset of MS, delay in diagnosis, initial symptoms, relapses features and behavior, EDSS and disease modifying therapy. They were subjected to DTI-MRI and blood sampling for GFAP. Results. DTI was able to differentiate between different MS phenotypes and was able to detect progression when we evaluated DTI changes in NAWM in different brain areas as low FA and high MD were associated with progression and increasing disability (p value =0.001). Serum GFAP differs significantly between patients with SPMS or patients in transition, also, it was higher in patients in transition than RRMS or control group (P value <0.001). There was a significant correlation between serum GFAP and DTI changes in NAWM as higher titres of GFAP were associated with lower FA and higher MD values in NAWM of frontal, temporal lobes, and CC body. Conclusion. Serum GFAP in addition to DTI measurable microdamage in NAWM can give us a wide scope of view about potential progression in MS pathology and related astrocytopathy.
Affecting 5% of all preschool-aged children and 1% of the general population, developmental stuttering—also called childhood-onset fluency disorder—is a complex, multifactorial neurodevelopmental ...disorder characterized by frequent disruption of the fluent flow of speech. Over the past two decades, neuroimaging studies of both children and adults who stutter have begun to provide significant insights into the neurobiological bases of stuttering. This review highlights convergent findings from this body of literature with a focus on functional and structural neuroimaging results that are supported by theoretically driven neurocomputational models of speech production. Updated views on possible mechanisms of stuttering onset and persistence, and perspectives on promising areas for future research into the mechanisms of stuttering, are discussed.
Diffusion magnetic resonance imaging (MRI) has been utilized to probe the renal microstructures but investigating the three-dimensional (3D) tubular network still presents significant challenges due ...to the complicated architecture of kidney. This study aims to assess whether high angular resolution diffusion imaging (HARDI) could improve the reconstruction of 3D tubular architectures. Kidneys from both mice and rats were imaged using 3D diffusion-weighted pulse sequences at 9.4 T. Five healthy mouse kidneys were scanned at an isotropic spatial resolution of 40 μm, with a b value of 1500 s/mm2 across 46 diffusion encoding directions. The study employed diffusion tensor imaging (DTI) and generalized Q-sampling imaging (GQI) to examine the tubular orientation distributions and tractography, validated by conventional histology. Fractional anisotropy (FA) and mean diffusivity (MD) were quantified and compared among the inner medullar (IM), outer medullar (OM), and cortex (CO) at different angular resolutions. FA values, estimated with 6 diffusion-weighted images (DWIs), were significantly overestimated by 49.9% (p < 0.001) in IM, 179.4% (p < 0.001) in OM, and 225.5% (p < 0.001) in CO, compared to using 46 DWIs. In contrast, MD exhibited less variations to angular resolution variations (3.4% in IM, 4.2% in OM, and 4.6% in CO). Both DTI and GQI at high angular resolution successfully traced renal tubular structures throughout the kidney, with GQI demonstrating superior performance in generating more continuous tracts. Furthermore, disrupted renal tubule structures were observed in a chronic kidney disease (CKD) rat model. HARDI, especially when combined with the GQI approach, holds promise in tracking complicated 3D tubule architectures and may serve as a potent tool for kidney disease research.
Display omitted
PDF
