Non-conventional MR techniques to monitor the evolution of multiple sclerosis

Metabolic changes in normal appearing white matter in multiple sclerosis patients using multivoxel magnetic resonance spectroscopy imaging

Demyelination and axonal degeneration caused by multiple sclerosis (MS) exist in the white matter and not only in the lesion area. Magnetic resonance spectroscopy (MRS) could provide a unique insight into metabolic changes in the normal appearing white matter (NAWM). To evaluate the subtle axonal degeneration and delineate the spatial distribution of metabolite abnormalities in the NAWM in patients with MS. A total of 17 clinically definite relapsing-remitting MS (RRMS) patients and 21 healthy controls were enrolled in this study. 2D 1H magnetic resonance spectroscopic imaging (MRSI) performed at 3 Tesla was used to measure metabolite concentrations in the frontal-parietal-occipital NAWM. Ratios of N-acetyl-aspartate (NAA) and choline (Cho) to creatine (Cr) and Cho to NAA were calculated in each voxel. MS patients showed decreased NAA/Cr and increased Cho/NAA ratios in the NAWM compared to healthy controls. In the parietal NAWM, the extent of NAA/Cr decrease was significantly higher than that in the frontal and parietal-occipital NAWM. Decreased NAA in the NAWM would provide useful metabolic information for evaluation of disease progression in MS. The high extent of NAA decrease in the parietal NAWM helps improve the accuracy of the prediction.

Chemical exchange saturation transfer of the cervical spinal cord at 7 T

High-magnetic-field (7 T) chemical exchange saturation transfer (CEST) MRI provides information on the tissue biochemical environment. Multiple sclerosis (MS) affects the entire central nervous system, including the spinal cord. Optimal CEST saturation parameters found via simulation were implemented for CEST MRI in 10 healthy controls and 10 patients with MS, and the results were examined using traditional asymmetry analysis and a Lorentzian fitting method. In addition, T1 - and T2 *-weighted images were acquired for lesion localization and the transmitted B1 (+) field was evaluated to guide imaging parameters. Distinct spectral features for all tissue types studied were found both up- and downfield from the water resonance. The z spectra in healthy subjects had the expected z spectral shape with CEST effects apparent from 2.0 to 4.5 ppm. The z spectra from patients with MS demonstrated deviations from this expected normal shape, indicating this method's sensitivity to known pathology as well as to tissues appearing normal on conventional MRI. Examination of the calculated CESTasym revealed increased asymmetry around the amide proton resonance (Δω = 3.5 ppm), but it was apparent that this measure is complicated by detail in the CEST spectrum upfield from water, which is expected to result from the nuclear Overhauser effect. The z spectra upfield (negative ppm range) were also distinct between healthy and diseased tissue, and could not be ignored, particularly when considering the conventional asymmetry analysis used to quantify the CEST effect. For all frequencies greater than +1 ppm, the Lorentzian differences (and z spectra) for lesions and normal-appearing white matter were distinct from those for healthy white matter. The increased frequency separation and signal-to-noise ratio, in concert with prolonged T1 at 7 T, resulted in signal enhancements necessary to detect subtle tissue changes not possible at lower field strengths. This study presents CEST imaging metrics that may be sensitive to the extensive and temporally varying biochemical neuropathology of MS in the spinal cord. Copyright © 2016 John Wiley & Sons, Ltd.

A Comparison of Magnetization Transfer Methods to Assess Brain and Cervical Cord Microstructure in Multiple Sclerosis

BACKGROUND

Demyelination is a core pathological feature of multiple sclerosis (MS) and spontaneous remyelination appears to be an important mechanism for repair in the disease. Magnetization transfer ratio imaging (MTR) has been used extensively to evaluate demyelination, although limitations to its specificity are recognized. MT saturation imaging (MTsat) removes some of the T1 dependence of MTR. We have performed a comparative evaluation of MTR and MTsat imaging in a mixed group of subjects with active MS, to explore their relative sensitivity to pathology relevant to explaining clinical outcomes.

METHODS

A total of 134 subjects underwent MRI of their brain and cervical spinal cord. Isotropic 3-dimensional pre- and postcontrast T1-weighted and T2-weighted fluid-attenuated inversion recovery (FLAIR) volumes were segmented into brain normal appearing white matter (NAWM), brain WM lesions (WML), normal appearing spinal cord (NASC), and spinal cord lesions. Volumes and metrics for MTR and MTsat histograms were calculated for each region.

RESULTS

Significant Spearman correlations were found with the Expanded Disability Status Scale and timed 25-foot walk for the whole brain and WML MTR, but not in that from the NAWM or any cervical spinal cord region. By contrast, the MTsat was correlated with both disability metrics in all these regions in both the brain and spine.

CONCLUSIONS

This study extends prior work relating atrophy and lesion load with disability, by characterization of MTsat parameters. MTsat is practical in routine clinical applications and may be more sensitive to tissue damage than MTR for both brain and cervical spinal cord.

Functional magnetic resonance imaging correlates of cognitive performance in patients with a clinically isolated syndrome suggestive of multiple sclerosis at presentation: an activation and connectivity study

Background/Objective: To assess whether abnormalities on functional magnetic resonance imaging (fMRI) are related to cognitive function in patients at presentation with clinically isolated syndrome (CIS) suggestive of multiple sclerosis.

Methods: Eighteen patients with CIS and 15 healthy controls (HCs) performed an adapted fMRI version of the Paced Auditory Serial Addition Test (PASAT). According to their PASAT performance, CIS patients were divided into two groups: 10 with a low PASAT performance (<1 SD from the mean value of HCs) were considered ‘cognitive impairment’ (CI); eight patients were defined as ‘cognitively preserved’ (CP). Between-group differences in the patterns of brain activations and effective connectivity were assessed.

Results: During PASAT, compared to HCs, CIS patients showed increased activations of the bilateral inferior parietal lobe (IPL), bilateral precuneus, bilateral middle frontal gyrus (MFG), left anterior cingulate cortex (ACC), left claustrum, right thalamus and right caudate nucleus. When CIS patients were analyzed, the CI group had a more significant activation of the bilateral IPL than HCs and CP patients. Compared to CP patients, they also had more significant recruitment of the right superior parietal lobe, right cerebellum, left MFG and left ACC. The analysis of effective connectivity showed stronger connections between several regions of the right hemisphere involved in working memory function in CI patients versus CP and HC.

Conclusions: During performance of the PASAT, CIS patients show abnormalities in the patterns of cortical recruitment and connectivity related to the level of their cognitive impairment.

Thalamic involvement and its impact on clinical disability in patients with multiple sclerosis: a diffusion tensor imaging study at 3T

BACKGROUND AND PURPOSE

Several studies suggest that grey matter involvement may play a role in multiple sclerosis (MS) pathology. Diffusion tensor imaging (DTI) at 3T was used to investigate the presence of damage to the normal-appearing thalamus in MS and its relationship with disability.

MATERIALS AND METHODS

Twenty-four patients with relapsing-remitting (RR, n = 13, age = 41.7 +/- 6.1, Expanded Disability Status Scale [EDSS] score = 2.2 +/- 1.2) and secondary-progressive (n = 11, age = 46.9 +/- 9.6, EDSS = 5.9 +/- 1.0) MS and 24 age- and sex-matched healthy volunteers were studied. Fractional anisotropy (FA) and mean diffusivity (MD) were measured in regions of interest of normal-appearing thalamus. We examined group differences in MD and FA and correlations between DTI-derived metrics and clinical or imaging measures of disease.

RESULTS

Patients with MS had higher thalamic FA (P < .0001) and MD (P = .035) than volunteers. MD values correlated with the Paced Auditory Serial Addition Task (r = -0.43, P = .034) and motor EDSS (r = 0.47, P = .021) scores. In patients with RRMS, MD values correlated with global EDSS (r = 0.75, P = .003) and motor EDSS (r = 0.68, P = .010). Correlations were found between MD values and T1 and T2 lesion load (r = 0.58, P < .05) and brain parenchymal fraction (r = -0.46, P < .05).

CONCLUSIONS

DTI was able to detect abnormalities in normal-appearing thalamus of patients with MS. The strength of association between thalamic DTI measures and functional impairment was in the same range as those seen with standard MR imaging disease measures. The assessment of the integrity of the thalamus with DTI is a promising metric as a marker of disease for future studies.

Structural and functional surrogates of cognitive impairment at the very early stage of multiple sclerosis

Following our previous reports based on parametric MRI methods (T(2)-weighted MRI, statistical mapping analysis of magnetization transfer ratio images and functional MRI) applied to a population of 18 patients with clinically isolated syndrome suggestive of multiple sclerosis, we have reviewed the possible structural and functional surrogates of MS that could explain the subtle cognitive impairment related to attention and working memory deficits evaluated with paced auditory serial addition test (PASAT). We propose that the brain substrates underlying cognitive impairment observed at the very early stage of MS are multifactorial. Several components could influence PASAT performances in patients: i) the extent of diffuse white matter damage, ii) the location of visible and non visible lesions, iii) the connectivity efficiency between distant brain functional areas involved in working memory processes and iv) the cortical reorganization. Nevertheless, individually, each of these parameters may have few influences on PASAT performance in patients. Using a multiregression model built with independent MR parameters, a very good evaluation of PASAT scores has been obtained in this limited number of patients explaining 90% of the variance. In conclusion, the different aspects of tissue and functional pathological brain underpinnings must be accounted to monitor accurately new therapeutic strategies for the treatment of early cognitive deficits related to MS.

Apparent diffusion coefficient (ADC) and magnetization transfer ratio (MTR) in pediatric hypoxic-ischemic brain injury

BACKGROUND AND PURPOSE

a review of the literature reveals the increasing interest in using Diffusion magnetic resonance imaging, with diffusion weighted images (DWI) and ADC (Apparent Diffusion Coefficient) quantitation, in pediatric hypoxic-ischemic brain injury. However, ADC and MTR (Magnetization Transfer Ratio) as quantitative tools have not been investigated together in these pathological conditions in young pediatric patients. The aim of this study was to apply a quantitative method by using ADC and MTR calculation in order to propose a reproducible quantitation of brain parenchymal lesions.

METHODS

we conducted a prospective study including all children presenting with suspected cerebral hypoxic-ischemic injury. 15 children were included, among them 10 males and 5 females aged from 36 weeks of gestation to 17 months with a median age of 10,5 months. All MR examinations were performed at 1.5 Tesla unit including conventional MR (T1, T2 and Inversion-recovery sequences) and DWI with ADC map. ADC and MTR ROI (region of interest) measurements were made, in the frontal subcortical and periventricular white matter (WM) as well as in the gray matter (GM=basal ganglia), and in focal lesions.

RESULTS

ADC and MTR values were abnormal in focal lesions and in diffuse injury with no evidence of lesion on conventional MRI and DWI. We observed a strong inverse correlation between these ADC and MTR (R=0,66 in WM; R=0,61 in GM).

CONCLUSION

ADC and MTR calculation may be helpful as a reproductive method to quantify the lesions and detect diffuse lesions in hypoxic-ischemic pediatric brain injury.

Imagerie en tenseur de diffusion et système nerveux central

Diffusion tensor MR imaging is a technique that provides details on tIssue microstructure and organization well beyond the usual image resolution. With diffusion tensor MR imaging, diffusion anisotropy can be quantified and subtle white matter changes not normally seen on conventional MRI can be detected. The purpose of this article is to review the current applications of diffusion tensor MR imaging for the study of the brain, including normal aging, Alzheimer's disease, neuropsychiatric disorders, strokes, multiple sclerosis, brain tumors and intractable seizures.