Changes In Fiber Tracts Research Articles

Alterations in white matter fiber tracts and their correlation with flying cadet behavior.

An increasing number of studies have shown that flight training alters the human brain structure; however, most studies have focused on gray matter, and the exploration of white matter structure has been largely neglected. This study aimed to investigate the changes in white matter structure induced by flight training and estimate the correlation between such changes and psychomotor and flight performance. Diffusion tensor imaging data were obtained from 25 flying cadets and 24 general college students. Data were collected in 2019 and 2022 and analyzed using automated fiber quantification. This study found no significant changes in the flight group in 2019. However, in 2022, the flight group exhibited significant alterations in the diffusion tensor imaging of the right anterior thalamic radiation, left cingulum cingulate, bilateral superior longitudinal fasciculus, and left arcuate fasciculus. These changes occurred within local nodes of the fiber tracts. In addition, we found that changes in fiber tracts in the 2022 flight group were correlated with the reaction time of the psychomotor test task and flight duration. These findings may help improve flight training programs and provide new ideas for the selection of excellent pilots.

Alterations in Diffusion Tensor Imaging-derived Indices of Auditory Pathway-related Fiber Tracts in Children With Sensorineural Hearing Loss.

Hearing loss is the most common sensory-neurological defect in humans. The most common hearing impairment is sensorineural hearing loss (SNHL) caused by the inner ear and related nerves. Diffusion tensor imaging (DTI) is an advanced MRI technique that can provide valuable information about auditory neural pathways and their microstructural changes. The present study was designed to investigate the microstructural changes in auditory pathways-related fiber tracts in children with SNHL. Twenty-two children including 11 subjects with SNHL aged 1-4 years and 11 healthy children were examined as controls. Then, DTI-derived parameters, such as fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AxD), and radial diffusivity (RD), and volume of fiber tracts were extracted from the inferior longitudinal fasciculus, acoustic radiation, and uncinate fasciculus. The results showed an increase in MD, RD, and AxD as well as a decrease in FA, volume, and diameter of auditory-pathway-related fiber tracts. Interestingly, there was an increase in the FA of acoustic radiation. White matter connections in the auditory canal decrease and AR integrity increases due to compensatory effects. These probably reflect atrophy or degradation as well as compensatory cross-modal reorganization in the absence of auditory input and the use of sign language. Diffusion tensor imaging (DTI) plays an important role in preoperative planning.Anatomical knowledge of the auditory tract is essential for lacrimal drainage surgeries, such as cochlear implantation.DTI-based biomarkers for brain changes and allows us to better understand the pathophysiological changes of auditory tract.Microstructural changes in the fiber tracts associated with the auditory pathway can distinguish sensorineural hearing loss (SNHL) from healthy subjects. Sensorineural hearing loss (SNHL) is the most common type and accounts for the majority of all hearing loss. SNHL is a congenital deficit and refers to any cause of hearing loss due to a pathology of the cochlea, auditory nerve, or central nervous system. One of the chief treatment planning is cochlear implant for these patients. So, it is necessary to evaluate the auditory system by imaging devices such as MRI (magnetic resonance imaging) before treatment. Diffusion tensor imaging tractography, or diffusion tensor imaging (DTI) tractography, is an MRI technique that measures the rate of water diffusion between cells to understand and create a map of the body's internal structures; it is most commonly used to provide imaging of the brain. The purpose of the present research was to assess the auditory system and its nerve routs in children before cochlear implant. This study showed that DT imaging is a novel approach for assessment of children with SNHL before and treatment.

Analysis of fractional anisotropy and mean diffusivity in refractory and non-refractory idiopathic generalized epilepsies

PurposeTo compare white matter bundles and fiber tract changes in seizure-free and non-seizure-free idiopathic generalized epilepsy (IGE) patients. MethodForty adult patients with IGE underwent a 3 T brain MRI with DTI sequences. According to seizure control status, eighteen patients were classified as refractory (R) if they had presented at least one incapacitating seizure in the previous six months, while on appropriate antiepileptic drug treatment. Twenty two seizure-free patients with adequate seizure control were considered non-refractory (NR). We compared fractional anisotropy (FA) and mean diffusivity (MD) values in sixteen white matter tracts in the R and NR groups, and in twenty healthy subjects. ResultsR and NR groups did not differ in gender, age and education. We found decreased FA in two tracts in the R group (forceps major and right uncinate fasciculus) and approaching statistical significance in two tracts in the NR group (right cingulate gyrus and right uncinate fasciculus) group, as well as increased MD in six tracts in the R group (forceps minor, left thalamic anterior radiation, right inferior longitudinal fasciculus, right longitudinal superior parietal and temporal fasciculi, and right cingulate gyrus) and in five tracts in the NR group (forceps minor, left thalamic anterior radiation, right inferior longitudinal fasciculus, right longitudinal superior parietal and temporal fasciculi), compared to controls. No differences were noted comparing FA and MD values between R and NR groups. ConclusionsIn our patient population, refractory IGE patients on adequate antiepileptic drug treatment did not present more severe white matter tract involvement compared to non-refractory patients.

Age-related changes in fiber tracts in healthy adult brains: A generalized q-sampling and connectometry study.

Generalized q-sampling (GQI) and connectometry analysis provide new indices, i.e., quantitative anisotropy (QA) and spin distribution function (SDF) in comparison with diffusion tensor imaging (DTI). They may provide more age-related changes in white matter (WM) in aging. To investigate the feasibility of using GQI and connectometry analysis to determine WM properties changes in aging. Cross-cohort research. Fifty normal adults (27 females) aged 21-71 years. T1 -weighted images (T1 WI) and high angular resolution diffusion imaging (HARDI) images were acquired at 1.5T. HARDI data were analyzed using DTI and GQI to obtain fractional anisotropy (FA), QA, fiber numbers, and fiber lengths for tract analysis and using q-space diffeomorphic reconstruction (QSDR) for the connectometry analysis. We compared differences of DTI, GQI, and connectometry analysis to reflect WM changes in aging. Associations between FA, QA, and fiber numbers and lengths and age were analyzed using Pearson's correlation coefficients. The connectometry analysis was conducted using a multiple linear regression analysis, including age and gender as factors. Uncorrected P-value/false discovery rate (FDR) (corrected for multiple comparisons) < 0.05 was considered statistically significant. More regional changes were detected in FA related to age than changes in QA (17 > 6 regions, P < 0.05). Fewer regional changes in fiber numbers and more changes of fiber lengths were observed for DTI than for GQI (5 < 8/10 > 7 regions, P < 0.05). However, DTI and GQI analyses revealed consistent results in some regions, including the genu of the corpus callosum (GCC), body of the corpus callosum (BCC), fornix (Fx), and anterior coronal radiation (ACR) (P < 0.05). The connectometry analysis showed more tract changes associated with age at an FDR of 0.05, which partially overlapped with the FA and QA. GQI and connectometry provide more information about age-related tracts and complement the DTI findings. 2 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2018;48:369-381.

ELEVATED CSF STREM2 IN AUTOSOMAL DOMINANTLY INHERITED ALZHEIMER’S DISEASE ASSOCIATED WITH REGIONAL FIBER TRACT INJURY: RESULTS FROM THE DIAN STUDY

The soluble fraction of the protein “triggering receptor expressed on myeloid cell 2” (sTREM2) is detectable in cerebrospinal fluid (CSF) and is a biomarker of microglial activation. In autosomal dominantly inherited Alzheimer's disease (ADAD), we recently showed that CSF-TREM2 levels are elevated up to seven years before the onset of dementia symptoms (Suárez-Calvet et al., Science Transl. Med. 2016). However, it is unclear whether higher microglia activation is associated with increased neurodegeneration. Here we assessed the association between CSF-sTREM2 levels and fiber-tract changes in ADAD, as measured by diffusion-tensor imaging (DTI). We included 59 mutation carriers (MC) and 44 non-carriers (NC) from the Dominantly Inherited Alzheimer Network (DIAN). Concentration of sTREM2 in CSF was determined with ELISA. Based on DTI, we used tract-based spatial statistics (TBSS) to produce skeletonized maps of mean diffusivity (MD). As a global measure of white matter damage, histogram peak-width of skeletonized-MD (PSMD) was applied. Estimated years from symptom onset (EYO), based on parental age-of-onset, were used as a measure of disease progression. First, we tested in regression analyses whether regional increases in MD (TBSS) and global PSMD were stronger in MC than NC (interaction EYOxMutation group), controlled for gender and education. Next, using similar regression models, we tested CSF-sTREM2 levels as a predictor of regional MD and global PSMD. For TBSS, the voxel-wise significance threshold was p<0.01 (uncorrected) and the cluster-extent threshold p<0.05 (FWE-corrected). The interaction EYOxMutation (t(73.6)=4.14, p<0.001) on PSMD indicated faster global fiber-tract alterations in MC compared to NC (Fig. 1A). TBSS analysis showed the increase in MD to be predominantly present within posterior fiber-tracts (inferior fronto-occipital fasciculus and forceps major) in MC (Fig. 1B, red colored). For CSF-sTREM2, higher levels were associated with increased global PSMD in MC but not NC (interaction: t(63.8)=2.34, p=0.021; Fig. 1C), where the regional effects clustered in the vulnerable posterior regions of the fiber-tracts (Fig. 1D, red colored).

Abstract TMP97: Demyelination, Cognition and Imaging in a Translational Model of Rat Vascular Cognitive Impairment

Small vessel disease and/or atherosclerosis produce microvascular and parenchymal inflammation in white matter and results in vascular cognitive impairment (VCI). We have performed bilateral carotid artery stenosis in hypertensive rats (SHR) to better understand disease pathology, targets for intervention and markers. Hypothesis: Complex cognitive deficits and diffuse fiber tract changes relevant to human VCI can be quantified and validated for future use. Methodology: We performed a series of behavioral assays to test declarative memory and executive functioning in stenosis compared to sham surgery SHR. Behavioral assays included T-maze decision making and alternation, novel object recognition (NOR) and active place avoidance (APA). MRI (DTI, DWI, Arterial Spin Labeling; ASL) and FDG-PET imaging was done in Corpus Callosum (CC). Histology-immunohistochemistry included measurements of microglia (Iba-1), astrocytes (GFAP) and Luxol fast blue (for myelin) in CC. Results: Stenosis resulted in consistent executive function decision making (T-maze) deficits (p&lt;0.05) and impaired complex cognitive performance (APA). No significant differences occurred between sham and stenosis animals in NOR and T-maze alternation. DTI analysis indicated significant (p&lt;0.05) changes in the CC of stenosis compared to sham SHR including: (1) decreased fractional anisotropy, (2) increased radial diffusivity, and (3) unchanged axial diffusivity. MRI ASL revealed significant (p&lt;0.05) decreases in white matter perfusion. No significant changes were seen in FDG-PET. In summary, stenosis animals exhibited increased white matter glial cell inflammation related to demyelination and lost cognition. The inflammatory microglia phenotype was verified using TNFα plus Iba-1 double staining. CC changes were significantly (p&lt;0.05) greater in the anterior, periventricular forebrain. Conclusion: We have successfully modeled the behavioral, imaging and histologic profile of human VCI in the rat. Currently pre/mature oligodendrocyte changes are being evaluated. This approach provides future opportunities to localize forebrain white matter changes using MR imaging parameters as markers for monitoring VCI demyelination/pathology and intervention.

Cingulum Correlates of Cognitive Functions in Patients with Mild Cognitive Impairment and Early Alzheimer’s Disease: A Diffusion Spectrum Imaging Study

Diffusion spectrum imaging (DSI) of MRI can detect neural fiber tract changes. We investigated integrity of cingulum bundle (CB) in patients with mild cognitive impairment (MCI) and early Alzheimer's disease (EAD) using DSI tractography and explored its relationship with cognitive functions. We recruited 8 patients with MCI, 9 with EAD and 15 healthy controls (HC). All subjects received a battery of neuropsychological tests to access their executive, memory and language functions. We used a 3.0-tesla MRI scanner to obtain T1- and T2-weighted images for anatomy and used a pulsed gradient twice-refocused spin-echo diffusion echo-planar imaging sequence to acquire DSI. Patients with EAD performed significantly poorer than the HC on most tests in executive and memory functions. Significantly smaller general fractional anisotropy (GFA) values were found in the posterior and inferior segments of left CB and of the anterior segment of right CB of the EAD compared with those of the HC. Spearman's correlation on the patient groups showed that GFA values of the posterior segment of the left CB were significantly negatively associated with the time used to complete Color Trails Test Part II and positively correlated with performance of the logical memory and visual reproduction. GFA values of inferior segment of bilateral CB were positively associated with the performance of visual recognition. DSI tractography demonstrates significant preferential degeneration of the CB on the left side in patients with EAD. The location-specific degeneration is associated with corresponding declines in both executive and memory functions.

Longitudinal Changes in Fiber Tract Integrity in Healthy Aging and Mild Cognitive Impairment: A DTI Follow-Up Study

Cross-sectional studies using diffusion tensor imaging (DTI) suggest decline of the integrity of intracortically projecting fiber tracts with aging and in neurodegenerative diseases, such as Alzheimer's disease (AD). Longitudinal studies on the change of fiber tract integrity in normal and pathological aging are still rare. Here, we prospectively studied 11 healthy elderly subjects and 14 subjects with amnestic mild cognitive impairment (MCI), a clinical risk group for AD, using high-resolution DTI and MRI at baseline and after 13 to 16 months follow-up. Fractional anisotropy (FA), a DTI measure of fiber tract integrity, was compared across time points and groups using a repeated measures linear model and tract based spatial statistics. Additionally, we determined rates of grey matter and white matter atrophy using automated deformation based morphometry. Healthy elderly subjects showed decline of FA in intracortical projecting fiber tracts, such as corpus callosum, superior longitudinal fasciculus, uncinate fasciculus, inferior fronto-occipital fasciculus, and cingulate bundle (p < 0.05, corrected for multiple comparisons). MCI subjects showed significant FA decline predominantly in the anterior corpus callosum (p < 0.05, corrected for multiple comparisons). Grey and white matter atrophy involved prefrontal, parietal, and temporal lobe areas in controls and prefrontal, cingulate, and parietal lobe areas in MCI subjects and agreed with the pattern of fiber tract changes. Our findings indicate that DTI allows detection of microstructural changes in subcortical fiber tracts over time that are related to aging as well as to early stages of AD type neurodegeneration. The underlying mechanisms for these changes are unknown.

Influence of User-Defined Parameters on Diffusion Tensor Tractography of the Corticospinal Tract

This study discusses the influence of user-defined parameters on fiber tracking results obtained from a standard deterministic streamline tractography algorithm. Diffusion tensor imaging with fiber tractography was performed in five healthy volunteers. A region of interest was highlighted in the ventral part of the pons at the level of the middle cerebellar peduncle. The parameters studied were angle threshold, fractional anisotropy threshold, step length and number of seed samples per voxel. Changes in fiber tracts were described for increasing values per parameter. Increasing the angle threshold resulted in more and longer fibers. A higher fractional anisotropy threshold resulted in decreased length and fiber tracts that were not representative. Increasing the step length decreased the fiber continuity and altered its position. A higher number of seed samples per voxel resulted in a higher fiber tract density. When interpreting diffusion tensor images, the reader should understand the influence of user-defined settings on the results, and should be aware of the inter-dependency of fiber tracking parameters.

A re-evaluation of the question of ascending fibers in the pyramidal tract

In 1952 we published a study in the cat with the Glees method, demonstrating the occurrence of degenerating fibers in the pyramidal tract rostral to transections of the tract in the spinal cord. These fibers were interpreted as spinocortical fibers, which have also been described in man. However, other authors have disputed the existence of such fibers. In an attempt to provide more information about this subject, multiple injections of horseradish peroxidase (free and lectin-labeled) were made in the sensorimotor cortex of 4 cats. No retrogradely labeled cells were found in the spinal cord in these cases. Our present and previously reported findings are discussed in the light of other studies of pathological changes in fiber tracts within the central nervous system. Although the present experiments were negative, the degenerating axons previously observed by us in silver sections from the pyramid, pons and internal capsule after lesions of the pyramidal tract in the spinal cord, can not be satisfactorily explained as evidence of retrograde, indirect Wallerian, degeneration of corticospinal fibers.