Relationships of brain white matter microstructure with clinical and MR measures in relapsing‐remitting multiple sclerosis

Purpose:

To assess the relationships of microstructural damage in the cerebral white matter (WM), as measured by diffusion tensor imaging (DTI), with clinical parameters and magnetic resonance imaging (MRI) measures of focal tissue damage in patients with multiple sclerosis (MS).

Materials and Methods:

Forty‐five relapsing‐remitting (RR) MS patients (12 male, 33 female; median age = 29 years, Expanded Disability Status Scale (EDSS) = 1.5, disease duration = 3 years) were studied. T2‐lesion masks were created and voxelwise DTI analyses performed with Tract‐Based Spatial Statistics (TBSS).

Results:

T2‐lesion volume (T2‐LV) was significantly (P < 0.05, corrected) correlated with fractional anisotropy (FA) in both lesions and normal‐appearing WM (NAWM). Relationships (P = 0.08, corrected) between increasing EDSS score and decreasing FA were found in the splenium of the corpus callosum (sCC) and along the pyramidal tract (PY). All FA associations were driven by changes in the perpendicular (to primary tract direction) diffusivity. No significant global and voxelwise FA changes were found over a 2‐year follow‐up.

Conclusion:

FA changes related to clinical disability in RR‐MS patients with minor clinical disability are localized to specific WM tracts such as the sCC and PY and are driven by changes in perpendicular diffusivity both within lesions and NAWM. Longitudinal DTI measurements do not seem able to chart the early disease course in the WM of MS patients. Imaging 2010; 31:309–316. © 2010 Wiley‐Liss, Inc.     

In vivo assessment of peripheral nerve regeneration by diffusion tensor imaging

Purpose

To evaluate the sensitivity of diffusion tensor imaging (DTI) in assessing peripheral nerve regeneration in vivo. We assessed the changes in the DTI parameters and histological analyses after nerve injury to examine degeneration and regeneration in the rat sciatic nerves.

Materials and Methods

For magnetic resonance imaging (MRI), 16 rats were randomly divided into two groups: group P (permanently crushed; n = 7) and group T (temporally crushed; n = 9). Serial MRI of the right leg was performed before the operation, and then performed at the timepoints of 1, 2, 3, and 4 weeks after the crush injury. The changes in fractional anisotropy (FA), axial diffusivity (λ_∥), and radial diffusivity (λ_?) were quantified. For histological analyses, the number of axons and the myelinated axon areas were quantified.

Results

Decreased FA and increased λ_? were observed in the degenerative phase, and increased FA and decreased λ_? were observed in the regenerative phase. The changes in FA and λ_? were strongly correlated with histological changes, including axonal and myelin regeneration.

Conclusion

DTI parameters, especially λ_?, can be good indicators for peripheral nerve regeneration and can be applied as noninvasive diagnostic tools for a variety of neurological diseases. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.

     

1H‐MR spectroscopy and diffusion tensor imaging of normal‐appearing temporal white matter in patients with nasopharyngeal carcinoma after irradiation: Initial experience

Purpose:

To detect radiation‐induced changes of temporal lobe normal‐appearing white mater (NAWM) following radiation therapy (RT) for nasopharyngeal carcinoma (NPC).

Materials and Methods:

Seventy‐five H¹‐MR spectroscopy and diffusion‐tensor imaging (DTI) examinations were performed in 55 patients before and after receiving fractionated radiation therapy (total dose; 66–75GY). We divided the dataset into six groups, a pre‐RT control group and five other groups based on time after completion of RT. N‐acetylaspartic acid (NAA)/choline (Cho), NAA/creatine (Cr), Cho/Cr, mean diffusibility (MD), functional anisotropy (FA), radial diffusibility (λ_?), and axial diffusibility (λ_||) were calculated.

Results:

NAA/Cho and NAA/Cr decreased and λ_? increased significantly within 1 year after RT compared with pre‐RT. After 1 year, NAA/Cho, NAA/Cr, and λ_? were not significantly different from pre‐RT. In all post‐RT groups, FA decreased significantly. λ_|| decreased within 9 months after RT compared with pre‐RT, but was not significantly different from pre‐RT more than 9 months after RT.

Conclusion:

DTI and H¹‐MR spectroscopy can be used to detect early radiation‐induced changes of temporal lobe NAWM following radiation therapy for NPC. Metabolic alterations and water diffusion characteristics of temporal lobe NAWM in patients with NPC after RT were dynamic and transient. J. Magn. Reson. Imaging 2013;37:101–108. © 2012 Wiley Periodicals, Inc.

     

Analysis of diffusion tensor imaging metrics for gliomas grading at 3 T

Objectives

To assess the diagnostic accuracy of axial diffusivity (AD), radial diffusivity (RD), apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values derived from DTI for grading of glial tumors, and to estimate the correlation between DTI parameters and tumor grades.

Methods

Seventy-eight patients with glial tumors underwent DTI. AD, RD, ADC and FA values of tumor, peritumoral edema and contralateral normal-appearing white matter (NAWM) and AD, RD, ADC and FA ratios: lowest average AD, RD, ADC and FA values in tumor or peritumoral edema to AD, RD, ADC and FA of NAWM were calculated.DTI parameters and tumor grades were analyzed statistically and with Pearson correlation. Receiver operating characteristic (ROC) curve analysis was also performed.

Results

The differences in ADC, AD and RD tumor values, and ADC and RD tumor ratios were statistically significant between grades II and III, grades II and IV, and between grades II and III–IV. The AD tumor ratio differed significantly among all tumor grades.Tumor ADC, AD, RD and glial tumor grades were strongly correlated. In the ROC curve analysis, the area under the curve (AUC) of the parameter tumor ADC was the largest for distinguishing grade II from grades III to IV (98.5%), grade II from grade IV (98.9%) and grade II from grade III (97.0%).

Conclusion

ADC, RD and AD are useful DTI parameters for differentiation between low- and high-grade gliomas with a diagnostic accuracy of more than 90%. Our study revealed a good inverse correlation between ADC, RD, AD and WHO grades II–IV astrocytic tumors.     

Multiple sclerosis: Hyperintense lesions in the brain on T1‐weighted MR images assessed by diffusion tensor imaging

Purpose:

To evaluate retrospectively quantitative diffusion tensor imaging (DTI) values of hyperintense lesions on nonenhanced T1‐weighted magnetic resonance (MR) images in patients with multiple sclerosis (MS) to elucidate the degree of demyelination or remyelination associated with T1 hyperintense lesions and study their relationship to MR markers of tissue damage (brain atrophy).

Materials and Methods:

Institutional review board approval was obtained; informed consent was waived for this HIPAA‐compliant study, including 76 patients with MS and 20 healthy control subjects without evidence of MS clinically or on imaging. T1 lesions were compared with normal white matter on nonenhanced images and judged to be hyperintense. Quantitative DTI metrics of T1 hyperintense lesions were examined, and the relationship between DTI parameters and brain atrophy were investigated in this study.

Results:

At least one T1 hyperintense lesion was found in 16 patients (total, 28 lesions). Hyperintense lesions on T1‐weighted imaging (T1WI) had lower mean diffusion (MD) than others signal intensity lesions on T1WI but higher MD than normal white matter (F = 3.931; P < 0.001); Fractional anisotropy (FA; F = 3.24; P < 0.001) and volume ratio (VR; F = 1.664; P < 0.001) were higher in hyperintense lesions on T1WI than hypointense/isointense lesions on T1WI, but were lower than normal‐appearing white matter (NAWM) and normal white matter in controls. There was correlation between FA and VR (r = 0.678; P < 0.001) and inverse correlation between FA and MD (r = ?0.437; P = 0.02), MD and VR (r = ?0.423; P 0.025) for T1 hyperintense lesion. The MD values of T1 hyperintense lesions (r = ?0.304; P < 0.001) and the VR values of T1 hyperintense lesions (r = 0.096; P = 0.042) were significantly (negative) correlated with Brain parenchymal fraction (BPF; higher BPF score); the FA values of T1 hyperintense lesions (r = ?0.111; P = 0.018), the MD values of T1 hyperintense lesions (r = 0.379; P < 0.001) and the VR values of T1 hyperintense lesions (r = ?0.142; P = 0.003) were significantly correlated with third ventricular width (lower width). However, the FA value of T1 hyperintense lesions was not significantly associated with BPF(r = 0.083; P = 0.08).

Conclusion:

The quantitative DTI values of T1 hyperintense MS plaques were between hypo‐/isointense lesions and NAWM or normal white matter, and correlated with BPF and third ventricular width. Our results supports the notion that axonal remyelination may be the reason for T1 hyperintense lesions. J. Magn. Reson. Imaging 2010;31:789–795. ©2010 Wiley‐Liss, Inc.

     

Combination of Mn2+‐enhanced and diffusion tensor MR imaging gives complementary information about injury and regeneration in the adult rat optic nerve

Purpose

To evaluate manganese (Mn²⁺)‐enhanced MRI (MEMRI) and diffusion tensor imaging (DTI) as tools for detection of axonal injury and regeneration after intravitreal peripheral nerve graft (PNG) implantation in the rat optic nerve (ON).

Materials and Methods

In adult Fischer rats, retinal ganglion cell (RGC) survival was evaluated in Flurogold (FG) back‐filled retinal whole mounts after ON crush (ONC), intravitreal PNG, and intravitreal MnCl₂ injection (150 nmol) at 0 and 20 days post lesion (dpl). MEMRI and echo‐planar DTI (DTI‐EPI) was obtained of noninjured ON one day after intravitreal MnCl₂ injection, and at 1 and 21 dpl after ONC, intravitreal PNG, and intravitreal MnCl₂ injections given at 0 and 20 dpl. GAP‐43 immunohistochemistry was performed after the last MRI.

Results

ONC reduced RGC density in retina by 94% at 21 dpl compared to noninjured ON without MnCl₂ injections. Both intravitreal PNG and intravitreal MnCl₂ injections improved RGC survival in retina, which was reduced by 90% (ONC+MnCl₂), 82% (ONC+PNG), and 74% (ONC+PNG+MnCl₂) compared to noninjured ON. DTI‐derived parameters (fractional anisotropy [FA], mean diffusivity, axial diffusivity λ_∥, and radial diffusivity λ_?) were unaffected by the presence of Mn²⁺ in the ON. At 1 dpl, CNR_MEMRI and λ_∥ were reduced at the injury site, while at 21 dpl they were increased at the injury site compared to values measured at 1 dpl. GAP‐43 immunoreactive axons were present in the ON distal to the ONC injury site.

Conclusion

MEMRI and DTI enabled detection of functional and structural degradation after rat ON injury, and there was correlation between the MRI‐derived and immunohistochemical measures of axon regeneration. J. Magn. Reson. Imaging 2009;29:39–51. © 2008 Wiley‐Liss, Inc.

     

Quantitative 3-T diffusion tensor imaging in detecting optic nerve degeneration in patients with glaucoma: association with retinal nerve fiber layer thickness and clinical severity

Introduction

To investigate the association of quantitative 3-T diffusion tensor imaging (DTI) with retinal nerve fiber layer (RNFL) thickness measured by optical coherence tomography (OCT) and clinical severity in detecting optic nerve degeneration in patients with primary closed-angle glaucoma.

Methods

Twenty three patients (42 eyes; 9 men, 14 women) with primary closed-angle glaucoma and 20 healthy controls were enrolled in this study. Both DTI and OCT were performed on the optic nerves of all subjects. The mean diffusivity (MD), fractional anisotropy (FA), and eigenvalue maps were obtained for quantitative analysis. RNFL thickness and quantitative electrophysiology were also performed on all subjects. The association of quantitative DTI with RNFL thickness and glaucoma stage was analyzed.

Results

Compared with control nerves, the FA, λ_‖, and λ_⊥ values, and RNFL thickness in affected nerves decreased, while MD increased in patients with primary glaucoma (p?<?0.05). There was a significant correlation between FA, MD, λ_‖, and λ_⊥ and the mean RNFL thickness (P?<?0.01). The mean FA and λ_⊥ values derived with DT MR imaging correlated well with glaucoma stage (P?<?0.05), but the mean MD and λ_‖ values did not correlate with glaucoma stage (P?>?0.05).

Conclusion

DTI measurement could detect abnormality of the optic nerve in patients with glaucoma and may serve as a biomarker of disease severity.     

Imaging age‐related cognitive decline: A comparison of diffusion tensor and magnetization transfer MRI

Purpose

To determine which MR technique was the most sensitive to age‐related white matter damage. We compared both diffusion tensor imaging (DTI) and magnetization transfer (MT) maps to determine which technique correlated most strongly with cognitive function in a middle‐aged and elderly community population.

Materials and Methods

In all, 64 healthy subjects (aged 50–90) underwent MRI and neuropsychology. Histograms were generated for white matter mean diffusivity (MD), fractional anisotropy (FA), and MT ratio (MTR). White matter hyperintensity volume (WMH) and brain volume were also determined. Composite neuropsychological scores were derived for 4 cognitive domains (executive function, working memory, episodic memory, and information processing speed).

Results

All MRI parameters correlated with age (FA r = 0.726, P < 0.001; MD r = ?0.619 P < 0.001, MTR r = ?0.566, P < 0.001, WMH r = 0.511, P < 0.001). All MRI parameters correlated with cognition, but DTI, and particularly FA, correlated most strongly. Adding DTI parameters explained more variance in cognition than WMH alone; the increase was greatest with FA, which alone explained 45%, 33%, and 25% of the variance in cognition for information processing speed, episodic memory, and executive function, respectively.

Conclusion

DTI appears the most sensitive imaging parameter to determine age‐related white matter damage. The stronger relationship with FA suggests that axonal damage is important in age‐related cognitive decline. J. Magn. Reson. Imaging 2009;29:23–30. © 2008 Wiley‐Liss, Inc.

     

Diffusion tensor and tensor metrics imaging in intracranial epidermoid cysts

Purpose

To explore the utility of diffusion tensor imaging (DTI) and diffusion tensor metrics (DTM) in characterizing the structural pathology of epidermoid cysts. DTI gives information about the tissue structure; a high fractional anisotropy (FA) indicates a highly structured orientation of the tissue, fibers, or white matter tracts. Based on the tensor rank, a set of three metrics has been described that can be used to measure the directional dependence of diffusion: linear anisotropy (CL), planar anisotropy (CP), and spherical anisotropy (CS). DTM takes into account the shape of diffusion anisotropy and hence may provide better insight into the orientation of structures than FA.

Materials and Methods

DTI was performed in three patients with epidermoid cysts. FA, directionally‐averaged mean diffusivity (Dav), exponential apparent diffusion coefficient (eADC), and DTM, such as CL, CP, and CS, were measured from the tumor core as well as from the normal‐appearing white matter. Histopathological correlation was obtained.

Results

Epidermoid cysts showed high FA with Dav values similar to that of normal white matter. eADC maps did not show any restriction of diffusion. FA values were high, but not as high as that for the white matter. CP values were higher and CL values were lower than those obtained for the white matter in various regions.

Conclusion

High CP values suggest preferential diffusion of water molecules along a two‐dimensional geometry, which could be attributed to the well‐structured orientation of keratin filaments and flakes within the tumor as demonstrated by histopathology. Advanced imaging modalities like DTI with DTM can provide information regarding the microstructural anatomy of the epidermoid cysts. J. Magn. Reson. Imaging 2009;29:967–970. © 2009 Wiley‐Liss, Inc.     

Quantitative assessment of the cervical spinal cord damage in neuromyelitis optica using diffusion tensor imaging at 3 Tesla

Purpose:

To investigate whether quantitative MRI measures of cervical spinal cord white matter (WM) using diffusion tensor imaging (DTI) in neuromyelitis optica (NMO) differed from controls and correlated with clinical disability.

Materials and Methods:

Ten referred patients and 12 healthy volunteers were imaged on a 3 Tesla scanner and patients were clinically assessed on the Expanded Disability Status Scale (EDSS). Two raters quantified DTI‐derived indices from all participants, including fractional anisotropy (FA), mean diffusivity (MD), parallel diffusivity (lambda[parallel]) and perpendicular diffusivity (lambda[perpendicular]) at C1–C6 for lateral and dorsal columns. After the inter‐rater reliability test, univariate correlations between DTI measures and disability were assessed using the Spearman's rho correlation coefficient. Multiple regression analysis was performed to investigate which DTI measures independently correlated with the clinical score.

Results:

Statistical test results indicated high reliability of all DTI measurements between two raters. NMO patients showed reduced FA, increased MD and lambda[perpendicular] compared with controls while lambda[parallel] did not show any significant difference. The former three DTI metrics also showed significant correlations with disability scores, and especially FA was found to be sensitive to mild NMO (EDSS ≤ 3)

Conclusion:

FA is a potentially useful quantitative biomarker of otherwise normal appearing WM damage in NMO. Such damage is associated with clinical disability. J. Magn. Reson. Imaging 2011;33:1312–1320. © 2011 Wiley‐Liss, Inc.     

Peripheral nerve diffusion tensor imaging (DTI): normal values and demographic determinants in a cohort of 60 healthy individuals

Objective

To identify demographic determinants of peripheral nerve diffusion tensor imaging (DTI) and to establish normal values for fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity (RD), and mean diffusivity (MD).

Methods

Sixty subjects were examined at 3 Tesla by single-shot DTI. FA, AD, RD, and MD were collected for the sciatic, tibial, median, ulnar, and radial nerve and were correlated with demographic variables.

Results

Mean FA of all nerves declined with increasing age (r = ?0.77), which could be explained by RD increasing (r = 0.56) and AD declining (r = ?0.40) with age. Moreover, FA was inversely associated with height (r = ?0.28), weight (r = ?0.38) and BMI (r = ?0.35). Although FA tended to be lower in men than women (p = 0.052), this difference became completely negligible after adjustment to body weight. A multiple linear regression model for FA was calculated with age and weight as predictors (defined by backward variable selection), yielding an R ² = 0.71 and providing a correction formula to adjust FA for age and weight.

Conclusion

Peripheral nerve DTI parameters depend on demographic variables. The most important determinants age and weight should be considered in all studies employing peripheral nerve DTI.

Key points

? Peripheral nerve diffusion tensor imaging (DTI) parameters depend on demographic variables. ? Fractional anisotropy (FA) declines with increasing age and weight. ? Gender does not systematically affect peripheral nerve DTI. ? The formula presented here allows adjustment of FA for demographic variables.

     

Assessment of corticospinal tract (CST) damage in acute stroke patients: Comparison of tract‐specific analysis versus segmentation of a CST template

Purpose:

To compare two techniques to assess corticospinal tract (CST) damage in stroke patients: tract‐specific analysis by probabilistic tractography and segmentation using a CST template.

Materials and Methods:

We extracted fractional anisotropy (FA) values, the FA ratio, and mean diffusivity (MD) in 18 stroke patients and 21 healthy volunteers matched for age and sex. We compared the two methods in order to determine their ability to detect 1) differences between diffusion tensor imaging (DTI) parameters of healthy volunteers and stroke patients, 2) the correlation between DTI parameters and clinical scores, and 3) the correlation between DTI parameters and blood oxygen level‐dependent (BOLD) signals in a fist‐closure task.

Results:

FA values were higher with the tractography approach than with the segmentation method, but differences between the ipsilesional CST and the homologous region in healthy subjects were detected using both methods. In patients, clinical scores were significantly correlated with FA values and FA ratios with both methods. The BOLD signal was positively correlated with FA values for CST with the segmentation but not with the tractography approach.

Conclusion:

CST damage in stroke patients can be assessed by either probabilistic tractography or segmentation of a CST template. Although each method has advantages and limitations, both are sensitive enough to detect differences among stroke patients and identify specific correlations with clinical scores. J. Magn. Reson. Imaging 2013;37:836–845. © 2012 Wiley Periodicals, Inc.     

Human cervical spinal cord funiculi: Investigation with magnetic resonance diffusion tensor imaging

Purpose:

To use spinal cord diffusion tensor imaging (DTI) for investigating human cervical funiculi, acquire axial diffusion magnetic resonance imaging (MRI) data with an in‐plane resolution sufficient to delineate subquadrants within the spinal cord, obtain corresponding DTI metrics, and assess potential regional differences.

Materials and Methods:

Healthy volunteers were studied with a 3 T Siemens Trio MRI scanner. DTI data were acquired using a single‐shot spin echo EPI sequence. The spatial resolution allowed for the delineation of regions of interest (ROIs) in the ventral, dorsal, and lateral spinal cord funiculi. ROI‐based and tractography‐based analyses were performed.

Results:

Significant fractional anisotropy (FA) differences were found between ROIs in the dorsal and ventral funiculi (P = 0.0001), dorsal and lateral funiculi (P = 0.015), and lateral and ventral funiculi (P = 0.0002). Transverse diffusivity was significantly different between ROIs in the ventral and dorsal funiculi (P = 0.003) and the ventral and lateral funiculi (P = 0.004). Tractography‐based quantifications revealed DTI parameter regional differences that were generally consistent with the ROI‐based analysis.

Conclusion:

Original contributions are: 1) the use of a tractography‐based method to quantify DTI metrics in the human cervical spinal cord, and 2) reported DTI values in various funiculi at 3 T. J. Magn. Reson. Imaging 2010;31:829–837. ©2010 Wiley‐Liss, Inc.     

Transmural heterogeneity of left ventricular myocardium remodeling in postinfarct porcine model revealed by MR diffusion tensor imaging

Purpose:

To investigate the transmural heterogeneity of left ventricular myocardium structural remodeling.

Materials and Methods:

Ex vivo diffusion tensor imaging (DTI) was performed in six adult porcine heart samples with apical septum infarction collected 13 weeks after permanent left anterior descending coronary artery ligation and six age‐matched intact controls. Alterations in diffusion indices and myocardial fiber orientation, including fractional anisotropy (FA), mean apparent diffusion coefficient (mean ADC), axial diffusivity (λ_∥), radial diffusivity (λ_?), and fiber helix angle were investigated at five transmural zones across myocardium wall in regions adjacent and remote to the infarct.

Results:

In both adjacent and remote regions of infarcted hearts, FA showed no significant alteration across transmural zones compared to controls. However, mean ADC, λ_∥, and λ_? exhibited significant decreases at endocardium zones but not epicardium zones. Moreover, myocardial fiber helix angle shifted towards left‐handed orientation at all transmural zones, especially in regions adjacent to the infarct, becoming more aligned with the epicardium fiber orientation.

Conclusion:

These experimental DTI findings indicate that the endocardium was more vulnerable to infarction, leading to more pronounced microstructural changes during remodeling. The current DTI approach reveals additional information in delineating postinfarct remodeling process, which may provide insights into cardiac mechanics and clinical assessment of cardiac diseases. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.

     

Directional diffusion of corticospinal tract supports therapy decisions in idiopathic normal-pressure hydrocephalus

Introduction

Gait disturbance in patients with idiopathic normal pressure hydrocephalus (iNPH) may be caused by alterations of the corticospinal tract that we aimed to measure with diffusion tensor imaging (DTI). The directional diffusion parameters axial diffusivity and fractional anisotropy (FA) reflect axon integrity, whereas mean diffusivity, radial diffusivity and magnetization transfer ratio (MTR) reflect myelin content.

Methods

Twenty-six patients with probable iNPH were grouped into drainage responders (n?=?12) and drainage non-responders (n?=?14) according to their improvement on gait assessment tests after a 3-day lumbar CSF drainage. We measured DTI and MTR of the corticospinal tract and, as reference, of the superior longitudinal fascicle before and after CSF withdrawal in iNPH and in ten age-matched controls. Drainage responders were re-examined after ventricoperitoneal shunting. Differences before any intervention and changes upon CSF withdrawal were evaluated.

Results

Axial diffusivity in corticospinal tract and superior longitudinal fascicle was higher in both patient groups compared to controls (p?<?0.001). Only in the corticospinal tract of drainage responders was FA higher compared to controls, and both FA and axial diffusivity decreased after shunting. For axial diffusivity upon CSF drainage, a decrease of >0.7 % discriminated drainage responders from drainage non-responders with 82 % sensitivity, and a decrease of >1 % predicted overall improvement after shunting with 87.5 % sensitivity and 75 % specificity. The specificity to discriminate responders/non-responders was low for all DTI values (max. 69 % for FA values).

Conclusion

High values of directional diffusion parameters in the corticospinal tract are found in iNPH patients indicating affection of its axons. Increased values and their decrease upon CSF drainage may facilitate treatment decisions in clinically uncertain cases.     

Monitoring of acute axonal injury in the swine spinal cord with EAE by diffusion tensor imaging

Purpose

To evaluate the ability of diffusion tensor imaging (DTI) to detect and monitor acute axonal injury in swine spinal cord with acute experimental allergic encephalomyelitis (EAE).

Materials and Methods

Magnetic resonance imaging of the cervical spinal cord was performed in vivo at different time points through the onset and progression of EAE using a 3 Tesla clinical scanner. The DTI parameters were calculated in four separate regions of interest at the C2/C3 level. The quantitative DTI‐pathology and DTI‐clinical correlations were verified.

Results

In the monophasic acute course of EAE onset and progression, axial diffusivity (AD) decrease correlates with acute axonal injury (r = ?0.84; P < 0.001). By contrast, radial diffusivity does not change and no demyelination in histopathology was detected. Moreover, a clear correlation between clinical disease and axial diffusivity was found in two swine EAE models (r = ?0.86; P < 0.001 and r = ?0.92; P < 0.001).

Conclusion

AD corresponds with axonal injury in the absence of demyelination and may be a useful noninvasive tool to investigate the underlying pathogenic processes of multiple sclerosis and to monitor the effects of experimental treatments for axonal injury. J. Magn. Reson. Imaging 2009;30:277–285. © 2009 Wiley‐Liss, Inc.

     

Diffusion tensor imaging of the median nerve in healthy and carpal tunnel syndrome subjects

Purpose

To determine if diffusion tensor imaging (DTI) of the median nerve could allow identification of patients with carpal tunnel syndrome (CTS).

Materials and Methods

A total of 13 healthy subjects and 9 CTS patients were scanned on a 3T magnetic resonance imaging (MRI) scanner. The MRI protocol included a DTI sequence from which the fractional anisotropy (FA), apparent diffusion coefficient (ADC), and the parallel and radial diffusivities could be extracted. Those parameters were quantified at different locations along the median nerve (proximal to the carpal tunnel, within the carpal tunnel, and distal to the carpal tunnel).

Results

At the carpal tunnel, the FA, radial diffusivity, and ADC differed significantly between healthy subjects and CTS patients (P < 0.0002). This highly significant difference between the two groups was due to an opposite trend of changes in the DTI indices between the proximal to the carpal tunnel and within the carpal tunnel locations. In healthy subjects the FA increased (+20%, P < 0.001) and the radial diffusivity and ADC decreased (by ?15% and ?8%, respectively, P < 0.05) between the proximal to the carpal tunnel and within the carpal tunnel locations. In CTS subjects the FA decreased (by ?21%, P < 0.05) and the radial diffusivity increased (by +23%, P < 0.01) between the proximal to the carpal tunnel and within the carpal tunnel locations.

Conclusion

DTI enables visualization and characterization of the median nerve in healthy subjects and CTS patients. DTI indices show clear‐cut discrimination between the two groups and in fact enables the of use DTI in the diagnosis of CTS. J. Magn. Reson. Imaging 2009;29:657–662. © 2009 Wiley‐Liss, Inc.

     

Diffusion tensor imaging of forearm nerves in humans

Purpose:

To implement a diffusion tensor imaging (DTI) protocol for visualization of peripheral nerves in human forearm.

Materials and Methods:

This Health Insurance Portability and Accountability Act (HIPAA)‐compliant study was approved by our Institutional Review Board and written informed consent was obtained from 10 healthy participants. T₁‐ and T₂‐weighted turbo spin echo with fat saturation, short tau inversion recovery (STIR), and DTI sequences with 21 diffusion‐encoding directions were implemented to acquire images of the forearm nerves with an 8 channel knee coil on a 3T MRI scanner. Identification of the nerves was based on T₁‐weighted, T₂‐weighted, STIR, and DTI‐derived fractional anisotropy (FA) images. Maps of the DTI‐derived indices, FA, mean diffusivity (MD), longitudinal diffusivity (λ_//), and radial diffusivity (λ_?) along the length of the nerves were generated.

Results:

DTI‐derived maps delineated the forearm nerves more clearly than images acquired with other sequences. Only ulnar and median nerves were clearly visualized on the DTI‐derived FA maps. No significant differences were observed between the left and right forearms in any of the DTI‐derived measures. Significant variation in the DTI measures was observed along the length of the nerve. Significant differences in the DTI measures were also observed between the median and ulnar nerves.

Conclusion:

DTI is superior in visualizing the median and ulnar nerves in the human forearm. The normative data could potentially help distinguish normal from diseased nerves. J. Magn. Reson. Imaging 2012;36:920–927. © 2012 Wiley Periodicals, Inc.

     

Microstructural changes in patients with progressive supranuclear palsy: A diffusion tensor imaging study

Purpose:

To determine whether progressive supranuclear palsy (PSP) is associated with specific diffusion tensor imaging (DTI) patterns of diffusivity, anisotropy, and coherence in functionally relevant brain areas.

Materials and Methods:

In all, 17 PSP patients and 17 controls were scanned using a 3 T magnetic resonance imaging (MRI) scanner. Patients were assessed in the off‐medication condition using the Hoehn and Yahr staging and the United Parkinson's Disease Rating Scale, motor subscale (UPDRS‐III). Diffusion information were analyzed in relation to disease severity and subtypes.

Results:

Numerous changes in diffusion properties were identified in the subcortical areas. In the midbrain, fractional anisotropy (FA) decreased and MD (mean diffusivity) increased with disease progression. UPDRS‐III scores correlated positively with both FA in the caudate and MD in the pons. DTI analysis of disease subtypes demonstrated significant differences between PSP‐Parkinsonism and Steele‐Richardson‐Olszewski syndrome in axial diffusivity values in the putamen and globus pallidus, as well as in intervoxel diffusion coherence values in the middle cerebellar peduncle.

Conclusion:

Our findings, cautiously interpreted, demonstrate the advantage of using a functional imaging technique to aid in the specificity of defining more precisely the pathological processes taking place in white and gray matter regions in PSP. J. Magn. Reson. Imaging 2010;32:69–75. © 2010 Wiley‐Liss, Inc.     

Fractional anisotropy and diffusivity changes in thyroid-associated orbitopathy

Introduction

To investigate the extraocular muscle (EOM) changes in thyroid-associated orbitopathy (TAO) on DTI and the correlations between DTI parameters and clinical features.

Methods

Twenty TAO patients and 20 age- and sex-matched controls provided informed consent and were enrolled. Ten-directional DTI was acquired in orbit. Fractional anisotropy (FA), mean, axial, and radial diffusivities were obtained at medial and lateral EOMs in both orbits. EOM thickness was measured in patients using axial CT images. FA and diffusivities were compared between patients and controls. The relationships between DTI values and muscle thickness and exophthalmos were evaluated. DTI values compared between patients in active and inactive phases by clinical activity score of TAO. DTI values were also compared between acute and chronic stages by the duration of disease.

Results

In medial EOM, FA was significantly lower in patients (p < 0.001) and negatively correlated with muscle thickness (r = ?0.604, p < 0.001). Radial diffusivity was significantly higher in patients (p = 0.010) and correlated with muscle thickness (r = 0.349, p = 0.027). In lateral EOM, DTI values did not differ between patients and controls. In the acute stage, the diffusivities of the medial rectus EOM were increased compared with the chronic stage. DTI values of the medial and lateral rectus EOM did not differ significantly between active and inactive phases.

Conclusion

DTI can be used to diagnose TAO with FA and radial diffusivity change in EOM. Diffusivities can be used to differentiate acute and chronic stage of TAO. However, DTI values showed limitation in reflecting TAO activity according to the CAS.