The value of new magnetic resonance techniques in multiple sclerosis

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.

Reduced thalamic and cerebellar rest metabolism in relapsing-remitting multiple sclerosis, a positron emission tomography study: correlations to lesion load

Magnetic resonance imaging (MRI) is the main tool for detecting central nervous system lesions in MS. However, classical anatomical MRI is unable to assess exactly disease related injury in normal-appearing brain tissue and to give information about the functional consequences of the disease, explaining weak correlation frequently observed between lesion load and clinical data. Recently, functional brain imaging techniques have provided new insights concerning pathophysiological processes of the disease. Among them Positron Emission Tomography (PET), a sensitive technique to evaluate functional consequences of tissue injury in other neurological diseases, has rarely been used in MS. Seventeen Relapsing-Remitting (RR-) MS patients with low disability at the early stage of the disease underwent measurements of cerebral metabolic rate of glucose (rCMRglu) in resting state by PET using [(18)F] fluorodeoxyglucose (FDG) and assessment of regional cortical and white matter lesion volume (LV), using an in-house-developed semi-automatic method, was done at the same time on MRI. rCMRglu of MS patients was compared with rCMRglu of 18 normal control subjects using univariate SPM99 analysis through Matlab 5 and correlations between rCMRglu and LV were tested using multivariate linear regression using SPM99. Statistical threshold was set at p<0.05 corrected for multiple comparisons and correlations. Compared to controls, reduced rCMRglu was found in the right thalamus (p<0.001), in bilateral cerebellum (p<0.05 for right and p<0.01 for left) and the posterior part of left inferior parietal cortex (p<0.05). In addition, higher rCMRglu in patients compared to controls was observed in left inferior frontal cortex, left (anterior part) and right inferior parietal cortex (p<0.001). rCMRglu in right thalamus correlates negatively with different LV: total LV, total juxtacortical and/or overlapping cortico-subcortical LV, total and frontal deep white matter LV. rCMRglu of the right superior frontal cortex negatively correlated with total and parieto-occipital deep white matter LV. The results of this study, performed in a group of recent RR-MS patients with low disability, suggest that demyelinating lesions in MS mainly have a remote effect on cortical, basal ganglia and cerebellum metabolism and that regional cortical compensatory mechanisms may be observed concurrently.

Imaging in CNS lupus

The diagnosis of neuropsychiatric systemic lupus erythematosus (NPSLE) is complex not only on account of the heterogeneous nature of neurological presentation but also because of the difficulty of differentiating lupus-related pathology from other neuropsychiatric diseases. Magnetic resonance imaging (MRI) remains the gold standard for the non-invasive assessment of NPSLE but there are problems, both with sensitivity and specificity. Both T(2) quantitation and the use of gadolinium have shown promise in differentiating acute from chronic lesions. Nonetheless, the lack of sensitivity of conventional MRI has led to the exploration of other MR-based techniques. Magnetic resonance spectroscopy (MRS) allows the measurement of brain metabolites, whereas diffusion weighted imaging and diffusion tensor imaging allow assessment of white matter structure and integrity. MRS studies in NPSLE have consistently shown a reduction in N-acetyl aspartate (a neuronal marker). Diffusion weighted imaging has had only limited application in lupus and the results to date have shown abnormal diffusivity in lupus patients consistent with inflammation and loss of white matter structure. These techniques remain research tools at this early stage. Positron emission tomography (PET) and single photon emission computed tomography (SPECT) have also been explored as functional imaging tools in lupus and both appear to be more sensitive in detecting subtle brain changes in NPSLE but there are issues with specificity which deter their use in the clinical setting.

Efficacy of proton magnetic resonance spectroscopy in neurological diagnosis and neurotherapeutic decision making

Anatomic and functional neuroimaging with magnetic resonance imaging (MRI) includes the technology more widely known as magnetic resonance spectroscopy (MRS). Now a routine automated "add-on" to all clinical magnetic resonance scanners, MRS, which assays regional neurochemical health and disease, is therefore the most accessible diagnostic tool for clinical management of neurometabolic disorders. Furthermore, the noninvasive nature of this technique makes it an ideal tool for therapeutic monitoring of disease and neurotherapeutic decision making. Among the more than 100 brain disorders that fall within this broad category, MRS contributes decisively to clinical decision making in a smaller but growing number. In this review, we will cover how MRS provides therapeutic impact in brain tumors, metabolic disorders such as adrenoleukodystrophy and Canavan's disease, Alzheimer's disease, hypoxia, secondary to trauma or ischemia, human immunodeficiency virus dementia and lesions, as well as systemic disease such as hepatic and renal failure. Together, these eight indications for MRS apply to a majority of all cases seen. This review, which examines the role of MRS in enhancing routine neurological practice and treatment concludes: 1) there is added value from MRS where MRI is positive; 2) there is unique decision-making information in MRS when MRI is negative; and 3) MRS usefully informs decision making in neurotherapeutics. Additional efficacy studies could extend the range of this capability.

Clinical-MRI correlations in the secondary progressive phase of MS: lessons from the treatment trials

Conventional MRI techniques are sensitive to detect MS lesions and their change overtime. In relapsing-remitting MS correlations with clinical measures are weak suggesting a pathological heterogeneity of these lesions. There are less data available in secondary progressive phase of the disease. The best source for clinical MRI correlations analysis is the placebo arm of the published interferon beta trials. This review presents the main clinical-MRI findings from these trials then focuses on recent promising observations obtained with non conventional MRI techniques in SP MS patients.

Magnetic resonance imaging of multiple sclerosis

Although conventional magnetic resonance imaging (cMRI) is widely used for diagnosing multiple sclerosis (MS) and monitoring disease activity and evolution, the correlation between cMRI and clinical findings is far from strict. Among the reasons for this "clinical-MRI paradox," a major role has been attributed to the limited specificity of cMRI to the heterogeneous pathological substrates of MS and to its inability to quantify the extent of damage in the normal-appearing tissue. Modern quantitative MRI techniques have the potential to overcome some of the limitations of cMRI. Metrics derived from magnetization transfer and diffusion-weighted MRI enable one to quantify the extent of structural changes occurring within and outside macroscopic MS lesions with increased pathological specificity over cMRI. Magnetic resonance spectroscopy can add information on the biochemical nature of such changes, with the potential to improve significantly our ability to monitor inflammatory demyelination and axonal injury. Finally, functional MRI might provide new insights into the role of cortical adaptive changes in limiting the clinical consequences of white-matter structural damage. This review outlines the major contributions given by MRI-based techniques to the diagnostic work-up of MS patients, to the understanding of the pathobiology of the disease, and to the assessment of the effects of new experimental treatments.

Cognitive dysfunction in patients with mildly disabling relapsing-remitting multiple sclerosis: an exploratory study with diffusion tensor MR imaging

Previous studies assessing the magnetic resonance imaging (MRI) correlates of cognitive dysfunction in multiple sclerosis (MS) achieved conflicting results. Diffusion tensor (DT)-MRI provides metrics that are sensitive to the macro- and microscopic MS lesion load with increased specificity to the more destructive aspects of MS pathology than conventional imaging. We performed an exploratory study to assess the magnitude of the correlation between quantities derived from DT-MRI and measures of cognitive impairment in patients with relapsing-remitting (RR) MS.T2, T1, DT-MRI scans of the brain and an extensive battery of neuropsychological tests (exploring language, complex reasoning, attention and memory) were obtained from 34 RRMS patients. We measured T2 and T1 lesion volumes (LV) and brain volume. Average lesion mean diffusivity (D) and fractional anisotropy (FA) were calculated. D and FA histograms from the brain tissue (BT), the normal-appearing brain tissue (NABT), the normal-appearing white matter (NAWM) and the normal-appearing gray matter (NAGM) were also obtained. Nine patients (26.5%) were found to be cognitively impaired. Moderate correlations were found between symbol digit modalities test, verbal fluency test and 10/36 spatial recall test scores and T2 LV, T1 LV and average lesion, WBT, NABT, NAWM and NAGM values (r values ranging from -0.30 to -0.53). No correlations were found between any of the neuropsychological test scores and brain volume, average lesion FA and WBT FA.DT-MRI provides quantitative metrics that seem to reflect the severity of language, attention and memory deficits in patients with RRMS. This study also suggests that the extent and the intrinsic nature of the macroscopic lesions as well as the damage of the NAWM and NAGM all contribute to the neuropsychological deficits of RRMS patients.

Diffusion- and perfusion-weighted MR imaging in a patient with acute demyelinating encephalomyelitis (ADEM)

To monitor changes of brain tissue metabolism in acute demyelinating encephalitis (ADEM), we examined a patient with suspected ADEM by serial MRI including diffusion- and perfusion-weighted imaging (DWI, PWI). Within the inflammatory tissue, the apparent diffusion coefficients were reduced, normal, and increased. Perfusion varied between reduced and normal values, except for small hyperperfused regions. Combining standard MRI with DWI and PWI may elucidate different overlapping phases in cerebral inflammation.

Neuroimaging techniques in the diagnostic work-up of patients with the antiphospholipid syndrome

The detection of multisystemic involvement often leads to a correct diagnosis of the antiphospholipid syndrome (APS), even in cases with predominant neurologic manifestations. However, when central nervous system deficits are isolated and have a relapsing-remitting or a progressive course, other conditions must be carefully considered. In this context, the diagnostic accuracy of conventional magnetic resonance imaging (MRI) is hampered by its limited pathologic specificity, which is one of the reasons why no or only modest correlations have been found between the burden of MRI-visible lesions and other clinical or laboratory measures of disease severity in patients with APS. Neuroimaging techniques with a higher pathologic specificity than conventional MRI show promise in achieving diagnostic confidence earlier in the course of APS and in better monitoring the efficacy of therapeutic interventions.

Magnetization transfer and diffusion tensor MR imaging of the optic radiations and calcarine cortex from patients with Leber's hereditary optic neuropathy

Optic nerve abnormalities are easily detectable in patients with Leber's hereditary optic neuropathy (LHON), using magnetic resonance imaging (MRI). However, the presence of structural changes in the optic radiations and calcarine cortex of these patients is still an unresolved issue. In this study, we obtained magnetization transfer (MT) and diffusion tensor (DT) MRI to investigate the integrity of these structures in patients with LHON. Dual echo, MT- and DT-MRI scans of the brain were obtained from 10 men with LHON and 10 healthy sex- and age-matched controls. After image co-registration, we obtained MT ratio (MTR), average diffusivity (D) and fractional anisotropy (FA) maps. MTR, D and FA values for the white matter of the optic radiations and MTR and D values for the calcarine cortex were obtained using a region of interest (ROI) analysis. No macroscopic abnormalities were detected in any of the scans from LHON patients and controls. No statistically significant differences of MTR, D or FA values were found for any of the regions studied in LHON patients and healthy controls. Our results suggest that, in patients with LHON, the optic radiations and the calcarine cortex are spared from structural damage, both at a macroscopic and a microscopic level.