Effect of increasing diffusion gradient direction number on diffusion tensor imaging fiber tracking in the human brain

Increased prevalence of vertebrobasilar dolichoectasia in Parkinson's disease and its effect on white matter microstructure and network

This study aimed to investigate the prevalence of vertebrobasilar dolichoectasia (VBD) in Parkinson's disease (PD) patients and analyze its role in gray matter changes, white matter (WM) microstructure and network alterations in PD. This is a cross-sectional study including 341 PD patients. Prevalence of VBD in these PD patients was compared with general population. Diffusion tensor imaging and T1-weighted imaging analysis were performed among 174 PD patients with or without VBD. Voxel-based morphometry analysis was used to estimate gray matter volume changes. Tract-based spatial statistics and region of interest-based analysis were used to evaluate WM microstructure changes. WM network analysis was also performed. Significantly higher prevalence of VBD in PD patients was identified compared with general population. Lower fractional anisotropy and higher diffusivity, without significant gray matter involvement, were found in PD patients with VBD in widespread areas. Decreased global and local efficiency, increased hierarchy, decreased degree centrality at left Rolandic operculum, increased betweenness centrality at left postcentral gyrus and decreased average connectivity strength between and within several modules were identified in PD patients with VBD. VBD is more prevalent in PD patients than general population. Widespread impairments in WM microstructure and WM network involving various motor and nonmotor PD symptom-related areas are more prominent in PD patients with VBD compared with PD patients without VBD.

Diffusion-Weighted MR Neurography with Unidirectional Motion-Probing Gradient to Evaluate Lumbar Nerve Roots at 1.5T MR

Purpose

Recent studies have demonstrated the usefulness of diffusion-weighted MR neurography (DW MRN) for assessing nerve roots. This study aimed to evaluate the utility of DW MRN with a unidirectional motion-probing gradient (MPG) for the lumbar nerve roots at 1.5T MR.

Materials and Methods

Sixty-four lumbar spine MRI scans with DW MRN using anteroposterior unidirectional MPG were retrospectively analyzed. Any changes in the 512 lumbar spinal nerve roots from L3 to S1 were evaluated using T2-weighted imaging (T2WI), contrast-enhanced T1-weighted imaging (CE T1WI), and DW MRN, with agreement and correlation analysis.

Results

T2WI revealed compression of 78 nerve roots, and CE T1WI revealed 52 instances of nerve root enhancement. Sixty-seven nerve roots showed swelling and hyperintensity on DW MRN. A total of 42 nerve roots showed changes in the CE T1WI and DW MRN sequences. Moderate to substantial agreement and moderate positive correlation were observed between DW MRN and CE T1WI, as well as DW MRN and T2WI (κ = 0.59-0.65, ρ = 0.600-0.653).

Conclusion

DW MRN with unidirectional anteroposterior MPG can help evaluate neuritis-related changes in spinal nerve roots and could serve as a sequence capable of complementing or substituting gadolinium CE imaging.

Inter-vendor and inter-observer reliability of diffusion tensor imaging in the musculoskeletal system: a multiscanner MR study

BACKGROUND

To evaluate the inter-observer and inter-vendor reliability of diffusion tensor imaging parameters in the musculoskeletal system.

METHODS

This prospective study included six healthy volunteers three men (mean age: 42; range: 31-52 years) and three women (mean age: 36; range: 30-44 years). Each subject was scanned using different 3 Tesla magnetic resonance scanners from three different vendors at three different sites bilaterally. First, the intra-class correlation coefficient was used to determine between-observers agreement for overall measurements and clinical sites. Next, between-group comparisons were made through the nonparametric Friedman's test. Finally, the Bland-Altman method was used to determine agreement among the three scanner measurements, comparing them two by two.

RESULTS

A total of 792 measurement were calculated. ICC reported high levels of agreement between the two observers. ICC related to MD, FA, and RD measurements ranged from 0.88 (95% CI 0.85-0.90) to 0.95 (95% CI 0.94-0.96), from 0.85 (95% CI 0.81-0.88) to 0.95 (95% CI 0.93-0.96), and from 0.89 (0.85-0.90) to 0.92 (0.90-0.94). No statistically significant inter-vendor differences were observed. The Bland-Altmann method confirmed a high correlation between parameter values.

CONCLUSION

An excellent inter-observer and inter-vendor reliability was found in our study.

Levodopa responsiveness and white matter alterations in Parkinson's disease: A DTI-based study and brain network analysis: A cross-sectional study

BACKGROUND

Patients with Parkinson's disease (PD) present various responsiveness to levodopa, but the cause of such differences in levodopa responsiveness is unclear. Previous studies related the damage of brain white matter (WM) to levodopa responsiveness in PD patients, but no study investigated the relationship between the structural brain network change in PD patients and their levodopa responsiveness.

METHODS

PD patients were recruited and evaluated using the Unified Parkinson's Disease Rating Scale (UPDRS). Each patient received a diffusion tensor imaging (DTI) scan and an acute levodopa challenge test. The improvement rate of UPDRS-III was calculated. PD patients were grouped into irresponsive group (improvement rate < 30%) and responsive group (improvement rate ≥ 30%). Tract-based spatial statistics (TBSS), deterministic tracing (DT), region of interest (ROI) analysis, and automatic fiber identification (AFQ) analyses were performed. The structural brain network was also constructed and the topological parameters were calculated.

RESULTS

Fifty-four PD patients were included. TBSS identified significant differences in fractional anisotropy (FA) values in the corpus callosum and other regions of the brain. DT and ROI analysis of the corpus callosum found a significant difference in FA between the two groups. Graph theory analysis showed statistical differences in global efficiency, local efficiency, and characteristic path length.

CONCLUSION

PD patients with poor responsiveness to levodopa had WM damage in multiple brain areas, especially the corpus callosum, which might cause disruption of information integration of the structural brain network.

Assessment of peripheral neuropathy in type 2 diabetes by diffusion tensor imaging: A case-control study

OBJECTIVES

This study aimed to evaluate diabetes peripheral neuropathy (DPN) by diffusion tensor imaging (DTI) and explore the correlation between DTI parameters and electrophysiological parameters.

METHODS

We examined tibial nerve (TN) and common peroneal nerve (CPN) of 32 DPN patients and 23 healthy controls using T1-weighted magnetic resonance imaging and DTI. Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity (RD) of TN and CPN were measured and compared between groups. Spearman correlation coefficient was used to explore the relationship between DTI parameters and electrophysiology parameters in the DPN group. Diagnostic value was assessed by receiver operating characteristic (ROC) analysis.

RESULTS

In the DPN group, FA was decreased (p < 0.0001) and MD and RD were increased (p < 0.05, p < 0.001) in the TN and CPN compared with the values of healthy control group. Moreover, in the DPN group, FA was positively correlated with motor nerve conduction velocity (MCV) (p < 0.0001), and both MD and RD were negatively correlated with MCV (p < 0.05, p < 0.001). However, there was no correlation between AD and any electrophysiological parameters. Among all DTI parameters, FA displayed the best diagnostic accuracy, with an area under the ROC curve of 0.882 in TN and 0.917 in CPN.

CONCLUSION

FA and RD demonstrate appreciable diagnostic accuracy. Furthermore, they both have a moderate correlation with MCV.

Renal Damages in Deoxycorticosterone Acetate-Salt Hypertensive Rats: Assessment with Diffusion Tensor Imaging and T2-mapping

PURPOSE

This study aimed to investigate the feasibility of diffusion tensor imaging (DTI) and T2-mapping to assess temporal renal damage in deoxycorticosterone acetate-salt (DOCA-salt) hypertensive rats and compare the results with histopathologic and immunohistochemical findings.

PROCEDURES

After baseline renal magnetic resonance imaging (MRI), 24 out of 30 uninephrectomized Sprague-Dawley rats with DOCA-salt-induced hypertension were divided equally into four groups. Group 1 had renal MRI at weeks 2, 4, 6, and 8, and groups 2, 3, and 4 had MRI at weeks 2, 4, and 6, respectively. The remaining 6 rats were used as sham controls. The renal cortex and outer and inner stripes of the outer medulla were examined over time using fractional anisotropy (FA), apparent diffusion coefficient (ADC), and T2-mapping, and the results were compared with baseline values. The degree of glomerular and tubular injury, endothelial cell thickening, hyaline arteriolosclerosis, macrophage infiltration, microcyst formation, and fibrosis in different zones at different time points in the DOCA-salt rats were compared with controls.

RESULTS

Compared with baseline values, DOCA-salt rats demonstrated a significant decrease in renal cortical FA from week 4 to week 8 (0.244 ± 0.015 vs 0.172 ± 0.014-0.150 ± 0.016, P = 0.018-0.002), corresponding to significantly more glomerular damage, arteriolosclerosis, macrophage infiltration, and fibrosis. The DOCA-salt rats had significantly increased cortical ADC and T2 values at weeks 6 and 8 (1.778 ± 0.051 × 10^-3 mm²/s vs 1.872 ± 0.058-1.917 ± 0.066 × 10^-3 mm²/s; 93.7 ± 4.9 ms vs 98.0 ± 2.9-100.7 ± 4.0 ms, respectively, all P < 0.05), consistent with excessively fluid-filled microcysts (aquaporin-2+). Despite DOCA-salt rats harbored markedly increased fibrosis in outer and inner stripes of the outer medulla at weeks 6 and 8, only nonsignificant decreases in FA were observed in comparison with the controls suggesting that only limited microstructural changes were present.

CONCLUSIONS

Renal cortical FA is useful for the early detection and monitoring of renal damage in DOCA-salt hypertensive rats.

Diffusion tensor imaging of the sciatic nerve in Charcot-Marie-Tooth disease type I patients: a prospective case-control study

OBJECTIVES

This study aimed to evaluate whether diffusion tensor imaging (DTI) parameters and cross-sectional area (CSA) can differentiate between the sciatic nerve of Charcot-Marie-Tooth (CMT) disease type I (demyelinating form) patients and that of controls.

METHODS

This prospective comparison study included 18 CMT type I patients and 18 age/sex-matched volunteers. Magnetic resonance imaging including DTI and axial T2-weighted Dixon sequence was performed for each subject. Region of interest analysis was independently performed by two radiologists on each side of the sciatic nerve at four levels: hamstring tendon origin (level 1), lesser trochanter of the femur (level 2), gluteus maximus tendon insertion (level 3), and mid-femur (level 4). Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were calculated. The CSA of the sciatic nerve bundle was measured using axial water-only image at each level. Comparisons of DTI parameters between the two groups were performed using the two-sample t test and Mann-Whitney U test. Interobserver agreement analysis was also conducted.

RESULTS

Interobserver agreement was excellent for all DTI parameter analyses. FA was significantly lower at all four levels in CMT patients than controls. RD, MD, and CSA were significantly higher at all four levels in CMT patients. AD was significantly higher at level 2 in CMT patients.

CONCLUSION

DTI assessment of the sciatic nerve is reproducible and can discriminate the demyelinating nerve pathology of CMT type I patients from normal nerves. The CSA of the sciatic nerve is also a potential parameter for diagnosing nerve abnormality in CMT type I patients.

KEY POINTS

• Diffusion tensor imaging parameters of the sciatic nerve at proximal to mid-femur level revealed significant differences between the Charcot-Marie-Tooth disease patients and controls. • The cross-sectional area of the sciatic nerve was significantly larger in the Charcot-Marie-Tooth disease patients. • Interobserver agreement was excellent (intraclass coefficient > 0.8) for all diffusion tensor imaging parameter analyses.

Diffusion Tensor-Derived Properties of Benign Oligemia, True "at Risk" Penumbra, and Infarct Core during the First Three Hours of Stroke Onset: A Rat Model

Objective

The aim of this study was to investigate diffusion tensor (DT) imaging-derived properties of benign oligemia, true “at risk” penumbra (TP), and the infarct core (IC) during the first 3 hours of stroke onset.

Materials and Methods

The study was approved by the local animal care and use committee. DT imaging data were obtained from 14 rats after permanent middle cerebral artery occlusion (pMCAO) using a 7T magnetic resonance scanner (Bruker) in room air. Relative cerebral blood flow and apparent diffusion coefficient (ADC) maps were generated to define oligemia, TP, IC, and normal tissue (NT) every 30 minutes up to 3 hours. Relative fractional anisotropy (rFA), pure anisotropy (rq), diffusion magnitude (rL), ADC (rADC), axial diffusivity (rAD), and radial diffusivity (rRD) values were derived by comparison with the contralateral normal brain.

Results

The mean volume of oligemia was 24.7 ± 14.1 mm³, that of TP was 81.3 ± 62.6 mm³, and that of IC was 123.0 ± 85.2 mm³ at 30 minutes after pMCAO. rFA showed an initial paradoxical 10% increase in IC and TP, and declined afterward. The rq, rL, rADC, rAD, and rRD showed an initial discrepant decrease in IC (from −24% to −36%) as compared with TP (from −7% to −13%). Significant differences (p < 0.05) in metrics, except rFA, were found between tissue subtypes in the first 2.5 hours. The rq demonstrated the best overall performance in discriminating TP from IC (accuracy = 92.6%, area under curve = 0.93) and the optimal cutoff value was −33.90%. The metric values for oligemia and NT remained similar at all time points.

Conclusion

Benign oligemia is small and remains microstructurally normal under pMCAO. TP and IC show a distinct evolution of DT-derived properties within the first 3 hours of stroke onset, and are thus potentially useful in predicting the fate of ischemic brain.

Neighborhood resolved fiber orientation distributions (NRFOD) in automatic labeling of white matter fiber pathways

Accurate digital representation of major white matter bundles in the brain is an important goal in neuroscience image computing since the representations can be used for surgical planning, intra-patient longitudinal analysis and inter-subject population connectivity studies. Reconstructing desired fiber bundles generally involves manual selection of regions of interest by an expert, which is subject to user bias and fatigue, hence an automation is desirable. To that end, we first present a novel anatomical representation based on Neighborhood Resolved Fiber Orientation Distributions (NRFOD) along the fibers. The resolved fiber orientations are obtained by generalized q-sampling imaging (GQI) and a subsequent diffusion decomposition method. A fiber-to-fiber distance measure between the proposed fiber representations is then used in a density-based clustering framework to select the clusters corresponding to the major pathways of interest. In addition, neuroanatomical priors are utilized to constrain the set of candidate fibers before density-based clustering. The proposed fiber clustering approach is exemplified on automation of the reconstruction of the major fiber pathways in the brainstem: corticospinal tract (CST); medial lemniscus (ML); middle cerebellar peduncle (MCP); inferior cerebellar peduncle (ICP); superior cerebellar peduncle (SCP). Experimental results on Human Connectome Project (HCP)'s publicly available "WU-Minn 500 Subjects + MEG2 dataset" and expert evaluations demonstrate the potential of the proposed fiber clustering method in brainstem white matter structure analysis.

Cortical microstructural changes along the Alzheimer's disease continuum

INTRODUCTION

Cortical mean diffusivity (MD) and free water fraction (FW) changes are proposed biomarkers for Alzheimer's disease (AD).

METHODS

We included healthy control subjects (N = 254), mild cognitive impairment (N = 41), and AD dementia (N = 31) patients. Participants underwent a lumbar puncture and a 3 T magnetic resonance imaging. Healthy control subjects were classified following National Institute on Aging-Alzheimer's Association stages (stage 0, N = 220; stage 1, N = 25; and stage 2/3, N = 9). We assessed the cortical MD, cortical FW, and cortical thickness (CTh) changes along the AD continuum.

RESULTS

Microstructural and macrostructural changes show a biphasic trajectory. Stage 1 subjects showed increased CTh and decreased MD and FW with respect the stage 0 subjects. Stage 2/3 subjects showed decreased CTh and increased cortical MD and FW, changes that were more widespread in symptomatic stages.

DISCUSSION

These results support a biphasic model of changes in AD, which could affect the selection of patients for clinical trials and the use of magnetic resonance imaging as a surrogate marker of disease modification.

Differentiation of the Infarct Core from Ischemic Penumbra within the First 4.5 Hours, Using Diffusion Tensor Imaging-Derived Metrics: A Rat Model

Objective

To investigate whether the diffusion tensor imaging-derived metrics are capable of differentiating the ischemic penumbra (IP) from the infarct core (IC), and determining stroke onset within the first 4.5 hours.

Materials and Methods

All procedures were approved by the local animal care committee. Eight of the eleven rats having permanent middle cerebral artery occlusion were included for analyses. Using a 7 tesla magnetic resonance system, the relative cerebral blood flow and apparent diffusion coefficient maps were generated to define IP and IC, half hour after surgery and then every hour, up to 6.5 hours. Relative fractional anisotropy, pure anisotropy (rq) and diffusion magnitude (rL) maps were obtained. One-way analysis of variance, receiver operating characteristic curve and nonlinear regression analyses were performed.

Results

The evolutions of tensor metrics were different in ischemic regions (IC and IP) and topographic subtypes (cortical, subcortical gray matter, and white matter). The rL had a significant drop of 40% at 0.5 hour, and remained stagnant up to 6.5 hours. Significant differences (p < 0.05) in rL values were found between IP, IC, and normal tissue for all topographic subtypes. Optimal rL threshold in discriminating IP from IC was about -29%. The evolution of rq showed an exponential decrease in cortical IC, from -26.9% to -47.6%; an rq reduction smaller than 44.6% can be used to predict an acute stroke onset in less than 4.5 hours.

Conclusion

Diffusion tensor metrics may potentially help discriminate IP from IC and determine the acute stroke age within the therapeutic time window.

The effect of diffusion gradient direction number on corticospinal tractography in the human brain: an along-tract analysis

OBJECTIVES

We evaluated diffusion imaging measures of the corticospinal tract obtained with a probabilistic tractography algorithm applied to data of two acquisition protocols based on different numbers of diffusion gradient directions (NDGDs).

MATERIALS AND METHODS

The corticospinal tracts (CST) of 18 healthy subjects were delineated using 22 and 66-NDGD data. An along-tract analysis of diffusion metrics was performed to detect possible local differences due to NDGD.

RESULTS

FA values at 22-NDGD showed an increase along the central portion of the CST. The mean of partial volume fraction of the orientation of the second fiber (f2) was higher at 66-NDGD bilaterally, because for 66-NDGD data the algorithm more readily detects dominant fiber directions beyond the first, thus the increase in FA at 22-NDGD is due to a substantially reduced detection of crossing fiber volume. However, the good spatial correlation between the tracts drawn at 22 and 66 NDGD shows that the extent of the tract can be successfully defined even at lower NDGD.

CONCLUSIONS

Given the spatial tract localization obtained even at 22-NDGD, local analysis of CST can be performed using a NDGD compatible with clinical protocols. The probabilistic approach was particularly powerful in evaluating crossing fibers when present.

A Novel Technique for Region and Linguistic Specific nTMS-based DTI Fiber Tracking of Language Pathways in Brain Tumor Patients

Navigated transcranial magnetic stimulation (nTMS) has recently been introduced as a non-invasive tool for functional mapping of cortical language areas prior to surgery. It correlates well with intraoperative neurophysiological monitoring (IONM) findings, allowing defining the best surgical strategy to preserve cortical language areas during surgery for language-eloquent tumors. Nevertheless, nTMS allows only for cortical mapping and postoperative language deficits are often caused by injury to subcortical language pathways. Nowadays, the only way to preoperatively visualize language subcortical white matter tracts consists in DTI fiber tracking (DTI-FT). However, standard DTI-FT is based on anatomical landmarks that vary interindividually and can be obscured by the presence of the tumor itself. It has been demonstrated that combining nTMS with DTI-FT allows for a more reliable visualization of the motor pathway in brain tumor patients. Nevertheless, no description about such a combination has been reported for the language network. The aim of the present study is to describe and assess the feasibility and reliability of using cortical seeding areas defined by error type-specific nTMS language mapping (nTMS-positive spots) to perform DTI-FT in patients affected by language-eloquent brain tumors. We describe a novel technique for a nTMS-based DTI-FT to visualize the complex cortico-subcortical connections of the language network. We analyzed quantitative findings, such as fractional anisotropy values and ratios, and the number of visualized connections of nTMS-positive spots with subcortical pathways, and we compared them with results obtained by using the standard DTI-FT technique. We also analyzed the functional concordance between connected cortical nTMS-positive spots and subcortical pathways, and the likelihood of connection for nTMS-positive vs. nTMS-negative cortical spots. We demonstrated, that the nTMS-based approach, especially what we call the “single-spot” strategy, is able to provide a reliable and more detailed reconstruction of the complex cortico-subcortical language network as compared to the standard DTI-FT. We believe this technique represents a beneficial new strategy for customized preoperative planning in patients affected by tumors in presumed language eloquent location, providing anatomo-functional information to plan language-preserving surgery.

Structural MR Imaging in the Diagnosis of Alzheimer's Disease and Other Neurodegenerative Dementia: Current Imaging Approach and Future Perspectives

With the rise of aging population, clinical concern and research attention has shifted towards neuroimaging of dementia. The advent of 3T, magnetic resonance imaging (MRI) has permitted the anatomical imaging of neurodegenerative disease, specifically dementia, with improved resolution. Furthermore, more powerful techniques such as diffusion tensor imaging, quantitative susceptibility mapping, and magnetic transfer imaging have successfully emerged for the detection of micro-structural abnormalities. In the present review article, we provide a brief overview of Alzheimer's disease and explore recent neuroimaging developments in the field of dementia with an emphasis on structural MR imaging in order to propose a simple and easily applicable systematic approach to the imaging diagnosis of dementia.