Diffusion Fiber Tractography Research Articles

Diffusion fiber tractography on phonological loop with Logopenic aphasia tau pathology: Fiber-specific white matter reductions in Alzheimer's disease, “is it a causal or casual link?”

Introduction Logopenic Aphasia (LA), a variant of primary progressive aphasia characterized with difficulty in retrieving precise words, names, or numbers and sentence repetition. Previous studies detailed that 50% of LA patients had (Alzheimer's disease) AD pathology, and characteristics of LA synchronize with language impairments in AD. Researchers believed that, the atrophy of Phonological loop (A sensorimotor circuit that includes auditory regions, the inferior parietal lobe, and Broca's area, which integrates phonological processing and executes motor output) cause LA. Methodology We focused on structural connectivity of Phonological loop using ;“Diffusion Imaging fiber Tractography;” with 60 DTI datasets (30 Males and 30 Females) of both control and progressive stages of Alzheimer's, with the age range 55–120 years, with IRB approval and made an attempt to correlate the Logopenic aphasia, with phonological loop fiber-specific white matter reductions in early AD. Results Overall progressive diminution was observed in the phonological loop of males (Figs 1 & 2) and left hemispheric deterioration is markedly seen in terms of both fibers and tract volume (significant at p

LEARNING 3D WHITE MATTER MICROSTRUCTURE FROM 2D HISTOLOGY.

Histological analysis is typically the gold standard for validating measures of tissue microstructure derived from magnetic resonance imaging (MRI) contrasts. However, most histological investigations are inherently 2-dimensional (2D), due to increased field-of-view, higher in-plane resolutions, ease of acquisition, decreased costs, and a large number of available contrasts compared to 3-dimensional (3D) analysis. Because of this, it would be of great interest to be able to learn the 3D tissue microstructure from 2D histology. In this study, we use diffusion MRI (dMRI) of a squirrel monkey brain and corresponding myelin stained sections in combination with a convolution neural network to learn the relationship between the 3D diffusion estimated axonal fiber orientation distributions and the 2D myelin stain. We find that we are able to estimate the 3D fiber distribution with moderate to high angular agreement with the ground truth (median angular correlation coefficients of 0.48 across the unseen slices). This network could be used to validate dMRI neuronal structural measurements in 3D, even if only 2D histology is available for validation. Generalization is possible to transfer this network to human stained sections to infer the 3D fiber distribution at resolutions currently unachievable with dMRI, which would allow diffusion fiber tractography at unprecedented resolutions. We envision the use of similar networks to learn other 3D microstructural measures from an array of potential common 2D histology contrasts.

Comparison of Microfiber Alteration of Fornix in Idiopathic Normal Pressure Hydrocephalus Patients, Alzheimer’s Disease Patients and Healthy Volunteers via Diffusion Tensor Imaging

Purpose: The clinical and imaging findings of idiopathic normal pressure hydrocephalus (iNPH) and Alzheimer's disease (AD) patients have some overlap and are often challenging to diagnose. The fornix is an important structure in the memory function, and damage to the fornix can result in memory impairment. Our study aimed to explore any differences in the microstructural changes to the fornices of iNPH and AD patients relative to those of normal control subjects, as demonstrated by using diffusion tensor imaging (DTI). Materials and methods: Ten normal control subjects, 10 iNPH patients and 10 AD patients underwent MRI scans (3-Tesla), and the DTI data were obtained. The DTI parameters and the diffusion fiber tractography were derived using DSI studio software. The differences in the fractional anisotropy (FA), apparent diffusion coefficient (ADC), axial diffusivity, and radial diffusivity data of the three groups were compared. A receiver operating characteristic (ROC) curve analysis was also evaluated. Results: There was a statistically-significant lower mean FA for the iNPH and AD patients than the normal control subjects. The mean ADC of the iNPH patients was statistically significantly higher than that of both the normal control subjects and the AD patients. The mean ADC is probably the most helpful parameter evident from our results, given its high sensitivity and high negative predictive value for discriminating between iNPH and AD patients. Conclusion: Our study revealed different microstructural changes in the fornices of iNPH and AD patients using the DTI technique. The results are probably due to differences in the pathogenesis of the diseases. Furthermore, our study demonstrated the possibility of using the DTI parameter as a supportive tool to discriminate between iNPH and AD patients with high sensitivity and a high negative predictive value.

Anatomical accuracy of standard-practice tractography algorithms in the motor system - A histological validation in the squirrel monkey brain

For two decades diffusion fiber tractography has been used to probe both the spatial extent of white matter pathways and the region to region connectivity of the brain. In both cases, anatomical accuracy of tractography is critical for sound scientific conclusions. Here we assess and validate the algorithms and tractography implementations that have been most widely used - often because of ease of use, algorithm simplicity, or availability offered in open source software. Comparing forty tractography results to a ground truth defined by histological tracers in the primary motor cortex on the same squirrel monkey brains, we assess tract fidelity on the scale of voxels as well as over larger spatial domains or regional connectivity. No algorithms are successful in all metrics, and, in fact, some implementations fail to reconstruct large portions of pathways or identify major points of connectivity. The accuracy is most dependent on reconstruction method and tracking algorithm, as well as the seed region and how this region is utilized. We also note a tremendous variability in the results, even though the same MR images act as inputs to all algorithms. In addition, anatomical accuracy is significantly decreased at increased distances from the seed. An analysis of the spatial errors in tractography reveals that many techniques have trouble properly leaving the gray matter, and many only reveal connectivity to adjacent regions of interest. These results show that the most commonly implemented algorithms have several shortcomings and limitations, and choices in implementations lead to very different results. This study should provide guidance for algorithm choices based on study requirements for sensitivity, specificity, or the need to identify particular connections, and should serve as a heuristic for future developments in tractography.

Alteration in the number and integrity of white matter tracts in the preterm: A quantitative diffusion tensor imaging and diffusion fibre tractography in children.

Purpose:Periventricular white matter is most commonly injured in preterm babies with hypoxia. To assess white matter damage, we decided to perform diffusion tensor imaging (DTI) in preterm children with history of hypoxia and magnetic resonance imaging (MRI) features of periventricular leukomalacia (PVL) (PTH). We hypothesized that the PTH have reduced number of white matter fibres compared to age matched pre term children without hypoxia (PTHO), and also depending on the severity of PVL, there could be reduction in the number of fibres as well.Materials and Methods:The present study was carried out at the Government Medical College, Thiruvananthapuram. DTI was performed on 15 PTH and 15 PTHO. We measured number of fibres and fractional anisotropy of corpus callosum (CC) and optic radiations (OR).Results:There was significant difference between two groups with regard OR (P < 0.001). The mean number of OR fibres in cases and control was 104 ± 28.44 (mean ± SD) and 578 ± 286 (mean ± SD), respectively. The mean number of CC in cases was 953 ± 429 and in controls was 1625 ± 116 with a P value <0.56. No significant difference in FA was seen between cases and controls (P = 0.94).Conclusions:Preterm children with history of hypoxia and MRI features of PVL show reduced number of CC and OR compared to preterm children without hypoxia. There was significant correlation between PVL severity and number of OR fibres which could be due to the preferential involvement of periventricular white matter, in which OR has a major contribution.

The B‐matrix must be rotated when correcting for subject motion in DTI data

To estimate diffusion tensor MRI (DTI) measures, such as fractional anisotropy and fiber orientation, reliably, a large number of diffusion-encoded images is needed, preferably cardiac gated to reduce pulsation artifacts. However, the concomitant longer acquisition times increase the chances of subject motion adversely affecting the estimation of these measures. While correcting for motion artifacts improves the accuracy of DTI, an often overlooked step in realigning the images is to reorient the B-matrix so that orientational information is correctly preserved. To the best of our knowledge, most research groups and software packages currently omit this reorientation step. Given the recent explosion of DTI applications including, for example, neurosurgical planning (in which errors can have drastic consequences), it is important to investigate the impact of neglecting to perform the B-matrix reorientation. In this work, a systematic study to investigate the effect of neglecting to reorient the B-matrix on DTI data during motion correction is presented. The consequences for diffusion fiber tractography are also discussed.

Dissociating the Human Language Pathways with High Angular Resolution Diffusion Fiber Tractography

The anatomical connectivity of ventrolateral frontal areas 44 and 45, which in the human brain constitute Broca's region, has been revisited on the basis of experimental anatomical tracer evidence in the nonhuman primate that the homologues of areas 44 and 45 have distinct bidirectional corticocortical connections. Here we show, using high angular resolution diffusion imaging in the living human brain, a dissociation between the specific projections from the pars opercularis (area 44) and the pars triangularis (area 45) in the ventrolateral frontal lobe. As in the macaque monkey, area 44 has distinct connections with the rostral inferior parietal lobule via the third branch of the superior longitudinal fasciculus. In contrast, area 45 connects with the superior temporal gyrus, anterior to Heschl's gyrus, via the extreme capsule fiber system. These results highlight the differences in connectivity between areas 44 and 45 which had previously been thought to be uniformly connected with the posterior temporal region via the arcuate fasciculus. We also provide evidence in the human brain that the arcuate fasciculus, as in the macaque monkey brain, connects the posterior superior temporal region with dorsolateral frontal areas 8 and rostral 6 that lie above areas 44 and 45. Thus, monkey and human evidence suggests that the connections of areas 44 and 45 are much more differentiated than had previously been thought and provide the basis for studies searching for their differential contribution in function.