A sensitive, noise-resistant method for identifying focal demyelination and remyelination in patients with multiple sclerosis via voxel-wise changes in magnetization transfer ratio

Quantitative magnetization transfer imaging in relapsing-remitting multiple sclerosis: a systematic review and meta-analysis

Myelin-sensitive MRI such as magnetization transfer imaging has been widely used in multiple sclerosis. The influence of methodology and differences in disease subtype on imaging findings is, however, not well established. Here, we systematically review magnetization transfer brain imaging findings in relapsing-remitting multiple sclerosis. We examine how methodological differences, disease effects and their interaction influence magnetization transfer imaging measures. Articles published before 06/01/2021 were retrieved from online databases (PubMed, EMBASE and Web of Science) with search terms including 'magnetization transfer' and 'brain' for systematic review, according to a pre-defined protocol. Only studies that used human in vivo quantitative magnetization transfer imaging in adults with relapsing-remitting multiple sclerosis (with or without healthy controls) were included. Additional data from relapsing-remitting multiple sclerosis subjects acquired in other studies comprising mixed disease subtypes were included in meta-analyses. Data including sample size, MRI acquisition protocol parameters, treatments and clinical findings were extracted and qualitatively synthesized. Where possible, effect sizes were calculated for meta-analyses to determine magnetization transfer (i) differences between patients and healthy controls; (ii) longitudinal change and (iii) relationships with clinical disability in relapsing-remitting multiple sclerosis. Eighty-six studies met inclusion criteria. MRI acquisition parameters varied widely, and were also underreported. The majority of studies examined the magnetization transfer ratio in white matter, but magnetization transfer metrics, brain regions examined and results were heterogeneous. The analysis demonstrated a risk of bias due to selective reporting and small sample sizes. The pooled random-effects meta-analysis across all brain compartments revealed magnetization transfer ratio was 1.17 per cent units (95% CI -1.42 to -0.91) lower in relapsing-remitting multiple sclerosis than healthy controls (z-value: -8.99, P < 0.001, 46 studies). Linear mixed-model analysis did not show a significant longitudinal change in magnetization transfer ratio across all brain regions [β = 0.12 (-0.56 to 0.80), t-value = 0.35, P = 0.724, 14 studies] or normal-appearing white matter alone [β = 0.037 (-0.14 to 0.22), t-value = 0.41, P = 0.68, eight studies]. There was a significant negative association between the magnetization transfer ratio and clinical disability, as assessed by the Expanded Disability Status Scale [r = -0.32 (95% CI -0.46 to -0.17); z-value = -4.33, P < 0.001, 13 studies]. Evidence suggests that magnetization transfer imaging metrics are sensitive to pathological brain changes in relapsing-remitting multiple sclerosis, although effect sizes were small in comparison to inter-study variability. Recommendations include: better harmonized magnetization transfer acquisition protocols with detailed methodological reporting standards; larger, well-phenotyped cohorts, including healthy controls; and, further exploration of techniques such as magnetization transfer saturation or inhomogeneous magnetization transfer ratio.

Higher EBV response is associated with more severe gray matter and lesion pathology in relapsing multiple sclerosis patients: A case-controlled magnetization transfer ratio study

BACKGROUND

Epstein-Barr virus (EBV) infection has been associated with higher clinical activity and risk of multiple sclerosis (MS).

OBJECTIVE

To evaluate associations between EBV-specific humoral response and magnetization transfer ratio (MTR)-derived measure in MS patients and healthy controls (HCs).

METHODS

The study included 101 MS patients (69 relapsing-remitting multiple sclerosis (RRMS) and 32 secondary-progressive multiple sclerosis (SPMS)) and 41 HCs who underwent clinical, serological, and magnetic resonance imaging (MRI) investigations. MTR values of T1 or T2 lesion volume (LV), normal-appearing (NA) brain tissue (NABT), gray matter (NAGM), and white matter (NAWM) were obtained. Enzyme-linked immunosorbent assay was used to quantify EBV antibody levels. Partial correlations corrected for MRI strength were used, and Benjamini-Hochberg-adjusted p-values < 0.05 were considered significant.

RESULTS

MS patients had significantly higher anti-EBV nuclear antigen-1 (EBNA-1) titer when compared to HCs (107.9 U/mL vs 27.8 U/mL, p < 0.001). Within the MS group, higher serum anti-EBNA-1 titer was significantly correlated with lower T1-LV MTR (r = -0.287, p = 0.035). Within the RRMS group, higher serum anti-EBNA-1 titer was associated with T1-LV MTR (r = -0.524, p = 0.001) and NAGM MTR (r = -0.308, p = 0.043). These associations were not present in HCs or SPMS patients.

CONCLUSION

Greater EBV humoral response is associated with lower GM MTR changes and focal destructive lesion pathology in RRMS patients.

Immunologic and MRI markers of the therapeutic effect of IFN-β-1a in relapsing-remitting MS

OBJECTIVES

To assess potential roles of effector cells and immunologic markers in demyelinating CNS lesion formation, and their modulation by interferon β-1a (IFN-β-1a).

METHODS

Twenty-three patients with relapsing-remitting multiple sclerosis (RRMS) received IFN-β-1a for 6 months. Immunologic marker results were correlated with brain MRI lesion volumes, and volumes of normal-appearing brain tissue (NABT) with decreasing or increasing voxel-wise magnetization transfer ratio (VW-MTR), suggestive of demyelination and remyelination, respectively.

RESULTS

Baseline expression of Th22 cell transcription factor aryl hydrocarbon receptor (AHR) and interleukin (IL)-17F, and percentages of IL-22-expressing CD4(+) and CD8(+) cells, were significantly higher in patients vs 15 healthy controls; IL-4 in CD4(+) cells was lower. Baseline percentage of IL-22-producing CD8(+) cells positively correlated with T2 lesion volumes, while percentage of IL-17A-producing CD8(+) cells positively correlated with T2 and T1 lesion volumes. IFN-β-1a induced reductions in transcription factor AHR, T-bet, and retinoic acid-related orphan nuclear hormone receptor C (RORc) gene expression, while it increased GATA3's expression in CD4(+) cells. Percentages of IL-22-, IL-17A-, and IL-17F-expressing T cells significantly decreased following treatment. Increased percentages of IL-10-expressing CD4(+) and CD8(+) cells correlated with greater NABT volume with increasing VW-MTR, while decreased percentage of IL-17F-expressing CD4(+) cells positively correlated with decreased NABT volume with decreasing VW-MTR.

CONCLUSIONS

Findings indicate that IFN-β-1a suppresses Th22 and Th17 cell responses, which were associated with decreased MRI-detectable demyelination.

CLASSIFICATION OF EVIDENCE

This pilot study provides Class III evidence that reduced Th22 and Th17 responses are associated with decreased demyelination following IFN-β-1a treatment in patients with RRMS.

Effect of treatment with interferon beta-1a on changes in voxel-wise magnetization transfer ratio in normal appearing brain tissue and lesions of patients with relapsing-remitting multiple sclerosis: a 24-week, controlled pilot study

Background

This pilot study investigated changes in remyelinating and demyelinating activity in normal appearing brain tissue (NABT) and lesions, by using voxel-wise magnetization transfer ratio (VW-MTR), in patients with relapsing–remitting multiple sclerosis (RRMS) receiving interferon beta-1a 44 mcg subcutaneously (IFN β-1a SC) three times weekly versus healthy controls (HCs) (NCT01085318).

Methods

Increasing (suggestive of remyelination) and decreasing (suggestive of demyelination) VW-MTR changes in NABT and in T2, T1 and gadolinium (Gd)-enhancing lesion volume were measured over 24 weeks in 23 patients treated with IFN β-1a SC and in 15 HCs (where applicable). VW-MTR changes were tested using the Wilcoxon signed–rank or Wilcoxon rank–sum test.

Results

A trend for greater volume of NABT with increasing VW-MTR at 24 weeks was observed for patients versus HCs (median [range] 1206 [0–15278]; 342 [0–951] mm³; p = 0.061). NABT volume with increasing VW-MTR at 12 weeks was significantly greater in patients than in HCs (852 [6–11577]; 360 [0–1755] mm³; p = 0.028). Similar findings were detected for lesion volumes. Two patients with notably high numbers of Gd-enhancing lesions at baseline had a markedly greater volume of tissue with increasing VW-MTR compared with other patients. Volume of NABT tissue with decreasing VW-MTR was significantly greater in patients versus HCs at 24 weeks (942 [0–6141]; 297 [0–852] mm³; p<0.001).

Conclusions

The significant change in NABT volume with increasing VW-MTR at 12 weeks suggests that active remyelination in patients with RRMS may occur during treatment with IFN β-1a SC. Findings from two patients with the highest number of Gd-enhancing lesions at baseline suggest that extensive remyelination in NABT may occur in patients with high disease activity. Tissue volume with decreasing VW-MTR was greater in patients than in HCs, despite treatment, validating the sensitivity of this technique for detecting MS disease activity.

Trial Registration

ClinicalTrials.gov NCT01085318.

A novel approach with "skeletonised MTR" measures tract-specific microstructural changes in early primary-progressive MS

We combined tract-based spatial statistics (TBSS) and magnetization transfer (MT) imaging to assess white matter (WM) tract-specific short-term changes in early primary-progressive multiple sclerosis (PPMS) and their relationships with clinical progression. Twenty-one PPMS patients within 5 years from onset underwent MT and diffusion tensor imaging (DTI) at baseline and after 12 months. Patients' disability was assessed. DTI data were processed to compute fractional anisotropy (FA) and to generate a common WM "skeleton," which represents the tracts that are "common" to all subjects using TBSS. The MT ratio (MTR) was computed from MT data and co-registered with the DTI. The skeletonization procedure derived for FA was applied to each subject's MTR image to obtain a "skeletonised" MTR map for every subject. Permutation tests were used to assess (i) changes in FA, principal diffusivities, and MTR over the follow-up, and (ii) associations between changes in imaging parameters and changes in disability. Patients showed significant decreases in MTR over one year in the corpus callosum (CC), bilateral corticospinal tract (CST), thalamic radiations, and superior and inferior longitudinal fasciculi. These changes were located both within lesions and the normal-appearing WM. No significant longitudinal change in skeletonised FA was found, but radial diffusivity (RD) significantly increased in several regions, including the CST bilaterally and the right inferior longitudinal fasciculus. MTR decreases, RD increases, and axial diffusivity decreases in the CC and CST correlated with a deterioration in the upper limb function. We detected tract-specific multimodal imaging changes that reflect the accrual of microstructural damage and possibly contribute to clinical impairment in PPMS. We propose a novel methodology that can be extended to other diseases to map cross-subject and tract-specific changes in MTR.

Voxel-wise magnetization transfer imaging study of effects of natalizumab and IFNβ-1a in multiple sclerosis

Objective:

To determine the effects of intravenous natalizumab and intramuscular interferon beta-1a (IFNβ-1a) on the volume of white-matter (WM) lesions and normal appearing brain tissue (NABT) undergoing voxel-wise (VW) increases in magnetization transfer ratio (MTR) suggestive of remyelination in patients with relapsing multiple sclerosis.

Methods:

This prospective, open-label, single-blinded study enrolled patients with relapsing–remitting multiple sclerosis (RRMS) and relapsing secondary progressive multiple sclerosis (RSPMS) as well as a group of age/sex-matched healthy controls ( n=22). Patients with multiple sclerosis were assigned to receive natalizumab monotherapy ( n=77; RRMS/RSPMS) or intramuscular IFNβ-1a ( n=26) as either monotherapy (RRMS) or combined with pulsed i.v. methylprednisolone, as needed (RSPMS). The primary endpoint was the two-year change in volume of NABT VWMTR, by quantifying the number of voxels that increased (suggesting remyelination) or decreased (suggesting demyelination) in their MTR value.

Results:

The volume of tissue undergoing increases in VWMTR was significantly larger in natalizumab compared with IFNβ-1a-treated patients (year 1: p=0.001 in NABT and p<0.006 in WM lesions; year 2: p=0.008 in NABT) and compared with healthy control subjects (year 1: p=0.05 and year 2: p=0.007 in NABT). The larger volume within NABT undergoing decreases in VWMTR was detected in multiple sclerosis patients compared with healthy controls ( p<0.001), and in the IFNβ-1a group compared with the natalizumab group (year 1: p=0.05; year 2: p=0.002). One patient on natalizumab died from progressive multifocal leukoencephalopathy eight months after completing the study.

Conclusion:

Natalizumab may promote remyelination and stabilize demyelination in lesions and NABT in relapsing multiple sclerosis, compared with intramuscular IFNβ-1a.

Brain region white matter associations with visual selective attention

To understand how normal variations in white matter relate to cognition, magnetization transfer imaging ratios (MTR) of a hypothesized neural network were associated with a test of visual selective attention (VST). Healthy adults (N = 16) without abnormal signal on brain scans viewed a version of DeSchepper and Treisman's test of VST (1996) with two levels of processing (novel shape matching with and without distractors, contingency feedback). A hypothesized neural network and component regions was significantly associated with accuracy and response times when distractors were present, with betas predicting 55% of variance in accuracy, and 59% of response times. MTR for anterior and posterior cingulate, prefrontal region, and thalami comprised a model predicting 55% of accuracy when distractors were present, and the anterior cingulate accounted for the majority of this effect. Prefrontal MTR predicted longer response times which was associated with increased accuracy. Distal neural areas involved in complex, processing-driven tasks (error processing, response selection, and variable response competition and processing load) may be dependent on white matter fibers to connect distal brain regions/nuclei of a macronetwork, including prefrontal executive functions.

Advanced MRI in multiple sclerosis: current status and future challenges

MRI has rapidly become a leading research tool in the study of multiple sclerosis (MS). Conventional imaging is useful in diagnosis and management of the inflammatory stages of MS but has limitations in describing the degree of tissue injury and cause of progressive disability seen in later stages. Advanced MRI techniques hold promise for filling this void. These imaging tools hold great promise to increase understanding of MS pathogenesis and provide greater insight into the efficacy of new MS therapies.

Regional variation, hemispheric asymmetries and gender differences in pericortical white matter

Brain white matter tissue composition can be quantified using Diffusion Tensor Imaging (DTI) and Magnetization Transfer Imaging (MTI). Fractional Anisotropy (FA), derived from DTI, indexes the integrity, density and organization of axons. Magnetization Transfer Ratio (MTR), derived from MTI, indexes to the presence of cell membranes and myelin. The combined use of FA and MTR provides a more complete picture of white matter structure than either imaging modality in isolation. Here we describe the regional distribution of FA and MTR measurements of pericortical white matter in 56 young, healthy right-handed subjects. Significant regional and lobar differences are seen for both measures along with a significant gender difference in FA. Highly consistent hemispheric asymmetries in FA and MTR were observed, suggesting that the greater fiber coherence and increased myelination of fibers in left hemisphere perisylvian regions may provide a structural basis for left-hemisphere language dominance.

Imaging central nervous system myelin by positron emission tomography in multiple sclerosis using [methyl-¹¹C]-2-(4'-methylaminophenyl)- 6-hydroxybenzothiazole

OBJECTIVE

Imaging of myelin tracts in vivo would greatly improve the monitoring of demyelinating diseases such as multiple sclerosis (MS). To date, no imaging technique specifically targets demyelination and remyelination. Recently, amyloid markers related to Congo red have been shown to bind to central nervous system (CNS) myelin. Here we questioned whether the thioflavine-T derivative 2-(4'-methylaminophenyl)-6-hydroxybenzothiazole (PIB), which also binds to amyloid plaques, could serve as a myelin marker.

METHODS

PIB fixation to myelin was studied by fluorescence in the normal and dysmyelinating mouse brain, as well as in the postmortem brain of MS patients. Positron emission tomography (PET) experiments were conducted using [¹¹C]PIB in baboons and in a proof of concept clinical study in 2 MS patients.

RESULTS

Applied directly on tissue sections or after intraperitoneal injection, PIB stained CNS myelin, and the decrease in the level of fixation paralleled the amount of myelin loss in a dysmyelinating mutant. In normally myelinated areas of postmortem MS brain, demyelinated and remyelinated lesions were clearly distinguishable by the differential intensity of labeling observed with PIB. PET using intravenously injected radiolabeled [¹¹C]PIB imaged CNS myelin in baboons and humans. In MS patients, the dynamic analysis of PET acquisitions allowed quantitative assessment of demyelination.

INTERPRETATION

PIB could be used as an imaging marker to quantify myelin loss and repair in demyelinating diseases.

Neuroimaging in multiple sclerosis: neurotherapeutic implications

Imaging techniques, in particular magnetic resonance imaging (MRI), play an important role in the diagnosis and management of multiple sclerosis (MS) and related demyelinating diseases. Findings on MRI studies of the brain and spinal cord are critical for MS diagnosis, are used to monitor treatment response and may aid in predicting disease progression in individual patients. In addition, results of imaging studies serve as essential biomarkers in clinical trials of putative MS therapies and have led to important insights into disease pathophysiology. Although they are useful tools and provide in vivo measures of disease-related activity, there are some important limitations of MRI findings in MS, including the non-specific nature of detectable white matter changes, the poor correlation with clinical disability, the limited sensitivity and ability of standard measures of gadolinium enhancing lesions and T2 lesions to predict future clinical course, and the lack of validated biomarkers of long term outcomes. Advancements that hold promise for the future include new techniques that are sensitive to diffuse changes, the increased use of higher field scanners, measures that capture disease related changes in gray matter, and the use of combined structural and functional imaging approaches to assess the complex and evolving disease process that occurs during the course of MS.

Advanced magnetic resonance imaging techniques to better understand multiple sclerosis

Magnetic resonance imaging (MRI) has considerably improved the diagnosis and monitoring of multiple sclerosis (MS). Conventional MRI such as T₂-weighted and gadolinium-enhanced T₁-weighted sequences detect focal lesions of the white matter, damage of the blood-brain barrier, and tissue loss and inflammatory activity within lesions. However, these conventional MRI metrics lack the specificity required for characterizing the underlying pathophysiology, especially diffuse damage occurring throughout the whole central nervous system. To overcome these limitations, advanced MRI techniques have been developed to get more sensitive and specific parameters of focal and diffuse brain damage. Among these techniques, magnetization transfer imaging, diffusion MRI, functional MRI, and magnetic resonance spectroscopy are the most significant. In this article, we provide an overview of these advanced MRI techniques and their contribution to the better characterization and understanding of MS.

Lesional magnetization transfer ratio: a feasible outcome for remyelinating treatment trials in multiple sclerosis

Magnetization transfer ratio (MTR) is a sensitive parameter to quantify the integrity of myelinated white matter in patients with multiple sclerosis. Lesional MTR decreases in the acute phase due to demyelination, and subsequently shows recovery depending on the degree of remyelination in the absence of axonal loss. Recovery of average lesion MTR therefore might prove a viable outcome measure to assess the effect of remyelinating agents. Our objective was to determine the required sample size for phase II multicentre clinical trials using the recovery of average lesion MTR as primary outcome measure. With 7-monthly MRI scans, the MTR evolution of 349 new enhancing lesions before and after enhancement was assessed in 32 MS patients from 5 centres. Multilevel models were fitted to the data yielding estimates for the variance components, which were applied in power calculations. Sample sizes were determined for placebo-controlled, multicentre trials using lesional MTR recovery post-enhancement as primary outcome measure. Average lesion MTR decreased slightly in the build-up to enhancement, decreased dramatically during enhancement and showed recovery in the period after cessation. The power calculations showed that for a power of 80%, approximately 136 patients per trial (mean number of 6 lesions per patient) are required to detect a 30% increase in lesional MTR post-enhancement compared with placebo, whereas 48 subjects are required to detect a 50% increase in lesional MTR compared with placebo. Recovery of lesion MTR is a feasible outcome measure for future multicentre clinical trials measuring the effect of remyelinating agents.