Conventional and magnetization transfer MRI predictors of clinical multiple sclerosis evolution: a medium-term follow-up study

Advanced Brain Imaging in Central Nervous System Demyelinating Diseases

In recent decades, advances in neuroimaging have profoundly transformed our comprehension of central nervous system demyelinating diseases. Remarkable technological progress has enabled the integration of cutting-edge acquisition and postprocessing techniques, proving instrumental in characterizing subtle focal changes, diffuse microstructural alterations, and macroscopic pathologic processes. This review delves into state-of-the-art modalities applied to multiple sclerosis, neuromyelitis optica spectrum disorders, and myelin oligodendrocyte glycoprotein antibody-associated disease. Furthermore, it explores how this dynamic landscape holds significant promise for the development of effective and personalized clinical management strategies, encompassing support for differential diagnosis, prognosis, monitoring treatment response, and patient stratification.

Magnetic resonance imaging prognostic factors for survival and relapse in dogs with meningoencephalitis of unknown origin

Introduction

Canine meningoencephalitis of unknown origin (MUO) is a debilitating disease associated with high mortality. The prognostic value of magnetic resonance imaging (MRI) findings for predicting survival at 12 months and long-term relapse remains uncertain.

Methods

This was a retrospective cohort study evaluating the prognostic value of different MRI variables using multivariable logistic regression and Cox proportional hazards analysis.

Results

In total, 138 dogs were presumptively diagnosed with MUO. The most common location for lesions identified on MRI were the white matter tracts of the corona radiata and corpus callosum, followed by the frontal, sensorimotor and temporal cortices. Lower T2 lesion load (p = 0.006, OR = 0.942, CI = 0.902-0.983) was associated with longer survival and higher T1 post-contrast lesion load (p = 0.023, OR = 1.162, CI = 1.021-1.322) was associated with relapse.

Discussion

This study has identified prognostic factors that may help identify dogs at higher risk of death and relapse and therefore guide treatment recommendations.

Only-train-once MR fingerprinting for B0 and B1 inhomogeneity correction in quantitative magnetization-transfer contrast

PURPOSE

To develop a fast, deep-learning approach for quantitative magnetization-transfer contrast (MTC)-MR fingerprinting (MRF) that simultaneously estimates multiple tissue parameters and corrects the effects of B0 and B1 variations.

METHODS

An only-train-once recurrent neural network was designed to perform the fast tissue-parameter quantification for a large range of different MRF acquisition schedules. It enabled a dynamic scan-wise linear calibration of the scan parameters using the measured B0 and B1 maps, which allowed accurate, multiple-tissue parameter mapping. MRF images were acquired from 8 healthy volunteers at 3 T. Estimated parameter maps from the MRF images were used to synthesize the MTC reference signal (Zref ) through Bloch equations at multiple saturation power levels.

RESULTS

The B0 and B1 errors in MR fingerprints, if not corrected, would impair the tissue quantification and subsequently corrupt the synthesized MTC reference images. Bloch equation-based numerical phantom studies and synthetic MRI analysis demonstrated that the proposed approach could correctly estimate water and semisolid macromolecule parameters, even with severe B0 and B1 inhomogeneities.

CONCLUSION

The only-train-once deep-learning framework can improve the reconstruction accuracy of brain-tissue parameter maps and be further combined with any conventional MRF or CEST-MRF method.

Temporal variability of serum miR-191, miR-223, miR-128, and miR-24 in multiple sclerosis: A 4-year follow-up study

BACKGROUND

Circulating microRNAs (miRNA) are suggested to be a promising biomarker for multiple sclerosis (MS). Previously, miR-128-3p, miR-24-3p, miR-191-5p and miR-223-3p have been reported to associate with MS pathology. However, their longitudinal changes and association with the disease activity have not been studied.

OBJECTIVES

To evaluate the serum temporal variability of miR-128-3p, miR-191-5p, miR-24-3p, and miR-223-3p and their association with disability and disease activity in MS.

METHODS

The expression of four miRNAs in serum was studied in 57 MS patients, 18 clinically isolated syndrome patients, and 32 healthy controls over the four-year follow-up.

RESULTS

At the baseline, miR-191-5p was overexpressed in RRMS in comparison to controls, and its levels correlated positively with EDSS and progression index (PI) in RRMS. Increased levels of miR-128-3p were detected in PPMS in comparison to controls, and increased levels correlated with EDSS and PI in RRMS. The expression of miR-24-3p and miR-223-3p did not differ between the subtypes, but miR-223-3p correlated negatively with T1 lesions volumes in SPMS and PPMS. Over the four-years follow-up period, the expression of miR-128-3p and miR-24-3p was stable longitudinally, while temporal changes of miR-191-5p and miR-223-3p were observed in MS. Temporal changes in miR-191-5p were observed to be associated with an increase of EDSS or MRI activity, while the variability of miR-223-3p was associated with relapses.

CONCLUSION

Temporal variability of miR-191-5p and miR-223-3p are associated with changes in disability accumulation and disease activity. While, miR-128-3p was stably expressed and associated with the PPMS subtype and correlated with disability accumulation.

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.

Pattern of Altered Magnetization Transfer Rate in Alzheimer's Disease

BACKGROUND

Biomarkers for Alzheimer's disease (AD) are crucial for early diagnosis and treatment monitoring once disease modifying therapies become available.

OBJECTIVE

This study aims to quantify the forward magnetization transfer rate (kfor) map from brain tissue water to macromolecular protons and use it to identify the brain regions with abnormal kfor in AD and AD progression.

METHODS

From the Cardiovascular Health Study (CHS) cognition study, magnetization transfer imaging (MTI) was acquired at baseline from 63 participants, including 20 normal controls (NC), 18 with mild cognitive impairment (MCI), and 25 AD subjects. Of those, 53 participants completed a follow-up MRI scan and were divided into four groups: 15 stable NC, 12 NC-to-MCI, 12 stable MCI, and 14 MCI/AD-to-AD subjects. kfor maps were compared across NC, MCI, and AD groups at baseline for the cross-sectional study and across four longitudinal groups for the longitudinal study.

RESULTS

We found a lower kfor in the frontal gray matter (GM), parietal GM, frontal corona radiata (CR) white matter (WM) tracts, frontal and parietal superior longitudinal fasciculus (SLF) WM tracts in AD relative to both NC and MCI. Further, we observed progressive decreases of kfor in the frontal GM, parietal GM, frontal and parietal CR WM tracts, and parietal SLF WM tracts in stable MCI. In the parietal GM, parietal CR WM tracts, and parietal SLF WM tracts, we found trend differences between MCI/AD-to-AD and stable NC.

CONCLUSION

Forward magnetization transfer rate is a promising biomarker for AD diagnosis and progression.

Quantitative magnetic resonance imaging towards clinical application in multiple sclerosis

Quantitative MRI provides biophysical measures of the microstructural integrity of the CNS, which can be compared across CNS regions, patients, and centres. In patients with multiple sclerosis, quantitative MRI techniques such as relaxometry, myelin imaging, magnetization transfer, diffusion MRI, quantitative susceptibility mapping, and perfusion MRI, complement conventional MRI techniques by providing insight into disease mechanisms. These include: (i) presence and extent of diffuse damage in CNS tissue outside lesions (normal-appearing tissue); (ii) heterogeneity of damage and repair in focal lesions; and (iii) specific damage to CNS tissue components. This review summarizes recent technical advances in quantitative MRI, existing pathological validation of quantitative MRI techniques, and emerging applications of quantitative MRI to patients with multiple sclerosis in both research and clinical settings. The current level of clinical maturity of each quantitative MRI technique, especially regarding its integration into clinical routine, is discussed. We aim to provide a better understanding of how quantitative MRI may help clinical practice by improving stratification of patients with multiple sclerosis, and assessment of disease progression, and evaluation of treatment response.

Quantitative MRI phenotypes capture biological heterogeneity in multiple sclerosis patients

Magnetization transfer ratio (MTR) and brain volumetric imaging are (semi-)quantitative MRI markers capturing demyelination, axonal degeneration and/or inflammation. However, factors shaping variation in these traits are largely unknown. In this study, we collected a longitudinal cohort of 33 multiple sclerosis (MS) patients and extended it cross-sectionally to 213. We measured MTR in lesions, normal-appearing white matter (NAWM), normal-appearing grey matter (NAGM) and total brain, grey matter, white matter and lesion volume. We also calculated the polygenic MS risk score. Longitudinally, inter-patient differences at inclusion and intra-patient changes during follow-up together explained > 70% of variance in MRI, with inter-patient differences at inclusion being the predominant source of variance. Cross-sectionally, we observed a moderate correlation of MTR between NAGM and NAWM and, less pronounced, with lesions. Age and gender explained about 30% of variance in total brain and grey matter volume. However, they contributed less than 10% to variance in MTR measures. There were no significant associations between MRI traits and the genetic risk score. In conclusion, (semi-)quantitative MRI traits change with ongoing disease activity but this change is modest in comparison to pre-existing inter-patient differences. These traits reflect individual variation in biological processes, which appear different from those involved in genetic MS susceptibility.

In vivo imaging of chronic active lesions in multiple sclerosis

New clinical activity in multiple sclerosis (MS) is often accompanied by acute inflammation which subsides. However, there is growing evidence that a substantial proportion of lesions remain active well beyond the acute phase. Chronic active lesions are most frequently found in progressive MS and are characterised by a border of inflammation associated with iron-enriched cells, leading to ongoing tissue injury. Identifying imaging markers for chronic active lesions in vivo are thus a major research goal. We reviewed the literature on imaging of chronic active lesion in MS, focussing on ‘slowly expanding lesions’ (SELs), detected by volumetric longitudinal magnetic resonance imaging (MRI) and ‘rim-positive’ lesions, identified by susceptibility iron-sensitive MRI. Both SELs and rim-positive lesions have been found to be prognostically relevant to future disability. Little is known about the co-occurrence of rims around SELs and their inter-relationship with other emerging techniques such as dynamic contrast enhancement (DCE) and positron emission tomography (PET).

Validated imaging biomarkers as decision-making tools in clinical trials and routine practice: current status and recommendations from the EIBALL* subcommittee of the European Society of Radiology (ESR)

Observer-driven pattern recognition is the standard for interpretation of medical images. To achieve global parity in interpretation, semi-quantitative scoring systems have been developed based on observer assessments; these are widely used in scoring coronary artery disease, the arthritides and neurological conditions and for indicating the likelihood of malignancy. However, in an era of machine learning and artificial intelligence, it is increasingly desirable that we extract quantitative biomarkers from medical images that inform on disease detection, characterisation, monitoring and assessment of response to treatment. Quantitation has the potential to provide objective decision-support tools in the management pathway of patients. Despite this, the quantitative potential of imaging remains under-exploited because of variability of the measurement, lack of harmonised systems for data acquisition and analysis, and crucially, a paucity of evidence on how such quantitation potentially affects clinical decision-making and patient outcome. This article reviews the current evidence for the use of semi-quantitative and quantitative biomarkers in clinical settings at various stages of the disease pathway including diagnosis, staging and prognosis, as well as predicting and detecting treatment response. It critically appraises current practice and sets out recommendations for using imaging objectively to drive patient management decisions.

Diffusion tensor imaging and disability progression in multiple sclerosis: A 4-year follow-up study

OBJECTIVES

Diffusion tensor imaging (DTI) is sensitive technique to detect widespread changes in water diffusivity in the normal-appearing white matter (NAWM) that appears unaffected in conventional magnetic resonance imaging. We aimed to investigate the prognostic value and stability of DTI indices in the NAWM of the brain in an assessment of disability progression in patients with a relapsing-onset multiple sclerosis (MS).

METHODS

Forty-six MS patients were studied for DTI indices (fractional anisotropy (FA), mean diffusivity (MD), radial (RD), and axial (AD) diffusivity) in the NAWM of the corpus callosum (CC) and the internal capsule at baseline and at 1 year after. DTI analysis for 10 healthy controls was also performed at baseline. Simultaneously, focal brain lesion volume and atrophy measurements were done at baseline for MS patients. Associations between DTI indices, volumetric measurements, and disability progression over 4 years were studied by multivariate logistic regression analysis.

RESULTS

At baseline, most DTI metrics differed significantly between MS patients and healthy controls. There was tendency for associations between baseline DTI indices in the CC and disability progression (p < 0.05). Changes in DTI indices over 1 year were observed only in the CC (p < 0.008), and those changes were not found to predict clinical worsening over 4 years. Clear-cut association with disability progression was not detected for baseline volumetric measurements.

CONCLUSION

Aberrant diffusivity measures in the NAWM of the CC may provide additional information for individual disability progression over 4 years in MS with the relapsing-onset disease. CC may be a good target for DTI measurements in monitoring disease activity in MS, and more studies are needed to assess the related prognostic potential.

Normal-appearing grey and white matter T1 abnormality in early relapsing–remitting multiple sclerosis: a longitudinal study

Objective

To investigate the presence and evolution of T1 relaxation time abnormalities in normal-appearing white matter (NAWM) and grey matter (GM), early in the course of relapsing–remitting multiple sclerosis (MS).

Methods

Twenty-three patients with early relapsing–remitting MS and 14 healthy controls were imaged six monthly for up to three years. Mean follow-up was 26 months for MS patients and 24 months for controls. Dual-echo fast-spin echo and gradient-echo proton-density and T1-weighted data sets (permitting the calculation of a T1 map) were acquired in all subjects. GM and NAWM T1 histograms were produced and a hierarchical regression model was used to investigate changes in T1 over time.

Results

At baseline, significant patient-control differences were seen, both in NAWM (P = 0.001) and in GM (P = 0.01). At follow-up, there was no evidence for a serial change in either mean T1 or peak-location for either NAWM or GM. There was weak evidence for a decline in patient NAWM peak-height and also evidence for a decline in control GM peak-height.

Conclusion

There are significant and persistent abnormalities of NAWM and GM T1 in early relapsing-remitting MS. Further studies should address whether such T1 measures have a role in prognosis or therapeutic monitoring. Multiple Sclerosis 2007; 13:169–177. http://msj.sagepub.com

In Vivo Brain MR Imaging at Subnanoliter Resolution: Contrast and Histology

This article provides an overview of in vivo magnetic resonance (MR) imaging contrasts obtained for mammalian brain in relation to histological knowledge. Emphasis is paid to the (1) significance of high spatial resolution for the optimization of T1, T2, and magnetization transfer contrast, (2) use of exogenous extra- and intracellular contrast agents for validating endogenous contrast sources, and (3) histological structures and biochemical compounds underlying these contrasts and (4) their relevance to neuroradiology. Comparisons between MR imaging at subnanoliter resolution and histological data indicate that (a) myelin sheaths, (b) nerve cells, and (c) the neuropil are most responsible for observed MR imaging contrasts, while (a) diamagnetic macromolecules, (b) intracellular paramagnetic ions, and (c) extracellular free water, respectively, emerge as the dominant factors. Enhanced relaxation rates due to paramagnetic ions, such as iron and manganese, have been observed for oligodendrocytes, astrocytes, microglia, and blood cells in the brain as well as for nerve cells. Taken together, a plethora of observations suggests that the delineation of specific structures in high-resolution MR imaging of mammalian brain and the absence of corresponding contrasts in MR imaging of the human brain do not necessarily indicate differences between species but may be explained by partial volume effects. Second, paramagnetic ions are required in active cells in vivo which may reduce the magnetization transfer ratio in the brain through accelerated T1 recovery. Third, reductions of the magnetization transfer ratio may be more sensitive to a particular pathological condition, such as astrocytosis, microglial activation, inflammation, and demyelination, than changes in relaxation. This is because the simultaneous occurrence of increased paramagnetic ions (i.e., shorter relaxation times) and increased free water (i.e., longer relaxation times) may cancel T1 or T2 effects, whereas both processes reduce the magnetization transfer ratio.

Evidence-based guidelines: MAGNIMS consensus guidelines on the use of MRI in multiple sclerosis-clinical implementation in the diagnostic process

The clinical use of MRI in patients with multiple sclerosis (MS) has advanced markedly over the past few years. Technical improvements and continuously emerging data from clinical trials and observational studies have contributed to the enhanced performance of this tool for achieving a prompt diagnosis in patients with MS. The aim of this article is to provide guidelines for the implementation of MRI of the brain and spinal cord in the diagnosis of patients who are suspected of having MS. These guidelines are based on an extensive review of the recent literature, as well as on the personal experience of the members of the MAGNIMS (Magnetic Resonance Imaging in MS) network. We address the indications, timing, coverage, reporting and interpretation of MRI studies in patients with suspected MS. Our recommendations are intended to help radiologists and neurologists standardize and optimize the use of MRI in clinical practice for the diagnosis of MS.

Magnetization transfer ratio in lesions rather than normal-appearing brain relates to disability in patients with multiple sclerosis

Magnetization transfer ratio (MTR) is a semi-quantitative measure that seems to correlate with the degree of myelin loss and generally tissue destruction in multiple sclerosis (MS). Our objective was to comprehensively assess the MTR of lesions and normal appearing (NA) tissue separately in the white matter (WM), the cortex, the thalamus and the basal ganglia (BG) and determine their relative contribution to disability. In this cross-sectional study 71 patients were included (59 with relapsing-remitting MS, 12 with secondary progressive MS). We used a three-dimensional MTR sequence with high spatial resolution, based on balanced steady-state free precession. Mean MTR was calculated for lesions and NA tissue separately for each tissue type. Lesional MTR was lower than normal-appearing MTR in WM, cortex and thalamus. In the regression analysis, MTR of cortical lesions (β = -0.23, p = 0.05) and MTR of WML (β = -0.21, p = 0.08) were related by trend to the expanded disability status scale. MTR of WML significantly predicted the paced auditory serial-addition test (β = 0.35, p = 0.004). MTR of normal-appearing tissue did not relate to any outcome. Our results suggest that MTR of lesions in the white matter and cortex rather than of normal-appearing tissue relates to disability in patients with MS.

Early magnetic resonance imaging predictors of clinical progression after 48 months in clinically isolated syndrome patients treated with intramuscular interferon β-1a

BACKGROUND AND PURPOSE

Our aim was to identify early imaging surrogate markers of clinical progression in patients after the first demyelinating event suggestive of multiple sclerosis treated with weekly intramuscular interferon β-1a. In a prospective observational study, the predictive role of baseline and 6-month changes in magnetic resonance imaging outcomes was investigated with respect to relapse activity and development of confirmed disability progression in patients after 48 months.

METHODS

This study examined 210 patients. Multivariate Cox proportional hazard models were used to analyse predictors of relapse activity and confirmed disability progression after 48 months.

RESULTS

Greater T2 lesion volume [hazard ratio (HR) 1.81; P = 0.005] and the presence of contrast-enhancing lesions (HR 2.13; P < 0.001) at baseline were significantly associated with increased cumulative risk of a second clinical attack over 48 months. A greater decrease of the corpus callosum volume (HR 2.74; P = 0.001) and greater lateral ventricle volume enlargement (HR 2.43; P = 0.002) at 6 months relative to baseline were associated with increased cumulative risk of a second clinical attack between months 6 and 48. In addition, increased risk of confirmed disability progression over 48 months in patients with greater lateral ventricle volume enlargement between baseline and 6 months (HR 4.70; P = 0.001) was detected.

CONCLUSIONS

A greater T2 lesion volume, the presence of contrast-enhancing lesions at baseline, decrease of corpus callosum volume and lateral ventricle volume enlargement over the first 6 months in patients after the first demyelinating event treated with weekly intramuscular interferon β-1a may assist in identification of patients with the highest risk of a second clinical attack and progression of disability.

Placebo-controlled trial of oral laquinimod in multiple sclerosis: MRI evidence of an effect on brain tissue damage

OBJECTIVE

In Assessment of OraL Laquinimod in PrEventing ProGRession in Multiple SclerOsis (ALLEGRO), a phase III study in relapsing-remitting multiple sclerosis (RRMS), oral laquinimod slowed disability and brain atrophy progression, suggesting laquinimod may reduce tissue damage in MS. MRI techniques sensitive to the most destructive aspects of the disease were used to further investigate laquinimod's potential effects on inflammation and neurodegeneration.

METHODS

1106 RRMS patients were randomised 1:1 to receive once-daily oral laquinimod (0.6 mg) or placebo for 24 months. White matter (WM), grey matter (GM) and thalamic fractions were derived at months 0, 12 and 24. Also assessed were evolution of gadolinium-enhancing and/or new T2 lesions into permanent black holes (PBH); magnetisation transfer ratio (MTR) of normal-appearing brain tissue (NABT), WM, GM and T2 lesions; and N-acetylaspartate/creatine (NAA/Cr) levels in WM.

RESULTS

Compared with placebo, laquinimod-treated patients showed lower rates of WM at months 12 and 24 (p=0.004 and p=0.035) and GM (p=0.004) atrophy at month 12 and a trend for less GM atrophy at month 24 (p=0.078). Laquinimod also slowed thalamic atrophy at month 12 (p=0.005) and month 24 (p=0.003) and reduced the number of PBH at 12 and 24 months evolving from active lesions (all p<0.05). By month 24, MTR decreased significantly in NABT (p=0.015), WM (p=0.011) and GM (p=0.034) in placebo-treated patients, but not in laquinimod-treated patients. WM NAA/Cr tended to increase with laquinimod and decrease with placebo at 24 months (p=0.179).

CONCLUSIONS

Oral laquinimod may reduce (at least in the initial phase of treatment) some of the more destructive pathological processes in RRMS patients.

TRIAL REGISTRATION

The ALLEGRO trial identifier number with clinicaltrials.gov is NCT00509145.

Insights from magnetic resonance imaging

Recent years have witnessed impressive advancements in the use of magnetic resonance imaging (MRI) for the assessment of patients with multiple sclerosis (MS). Complementary to the clinical evaluation, conventional MRI (cMRI) provides crucial pieces of information for the diagnosis of MS, the understanding of its natural history, and monitoring the efficacy of experimental treatments. Measures derived from cMRI present clear advantages over the clinical assessment, including their more objective nature and an increased sensitivity to MS-related changes. However, the correlation between these measures and the clinical manifestations of the disease remains weak, and this can be explained, at least partially, by the limited ability of cMRI to characterize and quantify the heterogeneous features of MS pathology. Quantitative MR-based techniques have the potential to overcome the limitations of cMRI. Magnetization transfer MRI, diffusion-weighted and diffusion tensor MRI with fiber tractography, proton magnetic resonance spectroscopy, T1 and T2 relaxation time measurement, and functional MRI are contributing to elucidate the mechanisms that underlie injury, repair, and functional adaptation in patients with MS. All conventional and nonconventional MR techniques will benefit from the use of high-field MR systems (3.0T or more).

Magnetization transfer and adiabatic T1ρ MRI reveal abnormalities in normal-appearing white matter of subjects with multiple sclerosis

BACKGROUND

Diffuse abnormalities are known to occur within the brain tissue of multiple sclerosis (MS) patients that is "normal appearing" on T1-weighted and T2-weighted magnetic resonance images.

OBJECTIVES

With the goal of exploring the sensitivity of novel MRI parameters to detect such abnormalities, we implemented an inversion-prepared magnetization transfer (MT) protocol and adiabatic T1ρ and T2ρ rotating frame relaxation methods.

METHODS

Nine relapsing-remitting MS patients and seven healthy controls were recruited. Relaxation parameters were measured in a single slice just above the lateral ventricles and approximately parallel to the AC-PC line.

RESULTS

The MT ratio of regions encompassing the normal-appearing white matter (NAWM) was different in MS patients as compared with controls (p = 0.043); however, the T1 measured during off-resonance irradiation (T1sat) was substantially more sensitive than the MT ratio for detecting differences between groups (p = 0.0006). Adiabatic T1ρ was significantly prolonged in the NAWM of MS patents as compared to controls (by 6%, p = 0.026), while no differences were found among groups for T2ρ. No differences among groups were observed in the cortical gray matter for any relaxation parameter.

CONCLUSIONS

The results suggest degenerative processes occurring in the NAWM of MS, likely not accompanied by significant abnormalities in iron content.

Neuroradiological evaluation of demyelinating disease

Central nervous system inflammatory demyelinating disease can affect patients across the life span. Consensus definitions and criteria of all of the different acquired demyelinating diseases that fall on this spectrum have magnetic resonance imaging criteria. The advances of both neuroimaging techniques and important discoveries in immunology have produced an improved understanding of these conditions and classification. Neuroimaging plays a central role in the accurate diagnosis, prognosis, disease monitoring and research efforts that are being undertaken in this disease. This review focuses on the imaging spectrum of acquired demyelinating disease.

Volumetric MRI markers and predictors of disease activity in early multiple sclerosis: a longitudinal cohort study

Objectives

To compare clinical and MRI parameters between patients with clinically isolated syndrome and those converting to clinically definite multiple sclerosis within 2 years, to identify volumetric MRI predictors of this conversion and to assess effect of early relapses.

Methods

The SET study comprised 220 patients with clinically isolated syndrome treated with interferon beta (mean age, 29 years; Expanded Disability Status Scale, 1.5). Three patients with missing data were excluded from the analysis. Physical disability, time to clinically definite multiple sclerosis and volumetric MRI data were recorded for 2 years.

Results

Patients reaching clinically definite multiple sclerosis showed impaired recovery of neurological function, faster decrease in corpus callosum cross-sectional area, higher T2 lesion volume and more contrast-enhancing lesions. Six-month decrease in corpus callosum cross-sectional area (≥1%) and baseline T2 lesion volume (≥5 cm³) predicted clinically definite multiple sclerosis within 2 years (hazard ratios 2.5 and 1.8, respectively). Of 22 patients fulfilling both predictive criteria, 83% reached clinically definite multiple sclerosis (hazard ratio 6.5). More relapses were associated with poorer recovery of neurological function and accelerated brain atrophy.

Conclusions

Neurological impairment is more permanent, brain atrophy is accelerated and focal inflammatory activity is greater in patients converting to clinically definite multiple sclerosis. Six-month corpus callosum atrophy and baseline T2 lesion volume jointly help predict individual risk of clinically definite multiple sclerosis. Early relapses contribute to permanent damage of the central nervous system.

Characterization of cerebral white matter properties using quantitative magnetic resonance imaging stains

The image contrast in magnetic resonance imaging (MRI) is highly sensitive to several mechanisms that are modulated by the properties of the tissue environment. The degree and type of contrast weighting may be viewed as image filters that accentuate specific tissue properties. Maps of quantitative measures of these mechanisms, akin to microstructural/environmental-specific tissue stains, may be generated to characterize the MRI and physiological properties of biological tissues. In this article, three quantitative MRI (qMRI) methods for characterizing white matter (WM) microstructural properties are reviewed. All of these measures measure complementary aspects of how water interacts with the tissue environment. Diffusion MRI, including diffusion tensor imaging, characterizes the diffusion of water in the tissues and is sensitive to the microstructural density, spacing, and orientational organization of tissue membranes, including myelin. Magnetization transfer imaging characterizes the amount and degree of magnetization exchange between free water and macromolecules like proteins found in the myelin bilayers. Relaxometry measures the MRI relaxation constants T1 and T2, which in WM have a component associated with the water trapped in the myelin bilayers. The conduction of signals between distant brain regions occurs primarily through myelinated WM tracts; thus, these methods are potential indicators of pathology and structural connectivity in the brain. This article provides an overview of the qMRI stain mechanisms, acquisition and analysis strategies, and applications for these qMRI stains.

Longitudinal changes in magnetisation transfer ratio in secondary progressive multiple sclerosis: data from a randomised placebo controlled trial of lamotrigine

Sodium blockade with lamotrigine is neuroprotective in animal models of central nervous system demyelination. This study evaluated the effect of lamotrigine on magnetisation transfer ratio (MTR), a putative magnetic resonance imaging measure of intact brain tissue, in a group of subjects with secondary progressive multiple sclerosis (MS). In addition, the utility of MTR measures for detecting change in clinically relevant pathology was evaluated. One hundred seventeen people attending the National Hospital for Neurology and Neurosurgery or the Royal Free Hospital, London, UK, were recruited into a double-blind, parallel-group trial. Subjects were randomly assigned by minimisation to receive lamotrigine (target dose 400 mg/day) or placebo for 2 years. Treating and assessing physicians and patients were masked to treatment allocation. Results of the primary endpoint, central cerebral volume, have been published elsewhere. Significant differences between the verum and placebo arms were seen in only two measures [normal appearing grey matter (NAGM) p = 0.036 and lesion peak height (PH) p = 0.004], and in both cases there was a greater reduction in MTR in the verum arm. Significant correlations were found of change in MS functional composite with all MTR measures except lesion and normal appearing white matter (NAWM) PH. However, the change in MTR measures over 2 years were small, with only NAGM mean (p = 0.001), lesion peak location (p = 0.11) and mean (p < 0.0001) changing significantly from baseline. These data did not show that lamotrigine was neuroprotective. The clinical correlation of MTR measures was consistent, but the responsiveness to change was limited.

Prediction of long-term disability in multiple sclerosis

BACKGROUND

Little is known about the predictive value of neurophysiological measures for the long-term course of multiple sclerosis (MS).

OBJECTIVE

To prospectively investigate whether combined visual (VEP) and motor evoked potentials (MEP) allow prediction of disability over 14 years.

METHODS

A total of 30 patients with relapsing-remitting and secondary progressive MS were prospectively investigated with VEPs, MEPs and the Expanded Disability Status Scale (EDSS) at entry (T0) and after 6, 12 and 24 months, and with cranial MRI scans at entry (T2-weighted and gadolinium-enhanced T1-weighted images). EDSS was again assessed at year 14 (T4). The association between evoked potential (EP), magnetic resonance (MR) data and EDSS was measured using Spearman's rank correlation. Multivariable linear regression was performed to predict EDSS(T4) as a function of z-transformed EP-latencies(T0). The model was validated using a jack-knife procedure and the potential for improving it by inclusion of additional baseline variables was examined.

RESULTS

EDSS values(T4) correlated with the sum of z-transformed EP-latencies(T0) (rho = 0.68, p < 0.0001), but not with MR-parameters(T0). EDSS(T4) as predicted by the formula EDSS(T4) = 4.194 + 0.088 * z-score P100(T0) + 0.071 * z-score CMCT(UE, T0) correlated with the observed values (rho = 0.69, p < 0.0001).

CONCLUSION

Combined EPs allow prediction of long-term disability in small groups of patients with MS. This may have implications for the choice of monitoring methods in clinical trials and for daily practice decisions.

Reproducibility of quantitative magnetization-transfer imaging parameters from repeated measurements

Quantitative magnetization-transfer imaging methods provide in vivo estimates of parameters of the two-pool model for magnetization-transfer in tissue. The goal of this study was to evaluate the reproducibility of quantitative magnetization-transfer imaging parameter estimates in healthy subjects. Magnetization-transfer-weighted and T(1) relaxometry data were acquired in five healthy subjects at multiple time points, and the variability of the resulting fitted magnetization-transfer parameters was evaluated. The impact of subsampling the magnetization-transfer data and correcting field inhomogeneities was also evaluated. The key parameters measured in this study had an average variability, across time points, of 4.7% for the relative size of the restricted pool (F), 7.3% for the forward exchange constant (k(f)), 1.9% for the free pool spin-lattice relaxation constant (R(1f)), 4.5% for the T(2) of the free pool (T(2f)), and 2.3% for the T(2) of the restricted pool (T(2r)). Our findings show that serial quantitative magnetization-transfer imaging experiments can be performed reliably, with good reproducibility of the model parameter estimates, and demonstrate the reproducibility of acquisition schemes with fewer magnetization-transfer contrasts. This establishes the feasibility of this technique for monitoring patients affected by degenerative white matter diseases while providing critical data to estimate the statistical power of such studies.

Imaging biomarkers in multiple sclerosis

Recent years have witnessed impressive advances in the use of magnetic resonance imaging (MRI) for the assessment of patients with multiple sclerosis (MS). Complementary to the clinical evaluation, conventional MRI provides crucial pieces of information for the diagnosis of MS. However, the correlation between the burden of lesions observed on conventional MRI scans and the clinical manifestations of the disease remains weak. The discrepancy between clinical and conventional MRI findings in MS is explained, at least partially, by the limited ability of conventional MRI to characterize and quantify the heterogeneous features of MS pathology. Other quantitative MR-based techniques, however, have the potential to overcome such a limitation of conventional MRI. Indeed, magnetization transfer MRI, diffusion tensor MRI, proton MR spectroscopy, and functional MRI are contributing to elucidate the mechanisms that underlie injury, repair, and functional adaptation in patients with MS. Such techniques are likely to benefit from the use of high-field MR systems and thus allow in the near future providing additional insight into all these aspects of the disease. This review summarizes how MRI is dramatically changing our understanding of the factors associated with the accumulation of irreversible disability in MS and highlights the reasons why they should be used more extensively in studies of disease evolution and clinical trials.

Neither retinal nor brain atrophy can be shown in patients with isolated unilateral optic neuritis at the time of presentation

Background:Acute monosymptomatic optic neuritis (ON) may be the earliest manifestation of multiple sclerosis (MS). Atrophy has been shown to be a prominent feature of MS with great impact on disability.

Objectives:The objectives of this study were to evaluate retinal and brain atrophy and possible associations at the earliest possible stages of MS.

Methods:In a prospective observational cohort study we included 60 untreated patients with monosymptomatic ON and 19 healthy volunteers. Unaffected fellow eyes were examined with optical coherence tomography (OCT) and normalized brain volumes were calculated based on MRI. Additionally, visual evoked potentials (VEPs) were recorded.

Results:Neither OCT measurements nor brain volume measures revealed signs of localized or generalized atrophy in patients compared with healthy volunteers. Stratification of patients into high risk based on the presence of white matter lesions did not reveal differences. The association between OCT measures and brain volumes previously found could not be confirmed at the time of the first clinical event. VEP latency was significantly prolonged in patients with white matter lesions compared to those without lesions. A trend towards a relationship between VEP amplitude of fellow eyes and brain volumes was noted.

Conclusions:In this cohort we were not able to show atrophic features in the retina or the brain, and the association between structural measures of the retina and the brain as indicated in the later stages of MS could not be reproduced. These findings suggest that atrophy does require time to evolve and indicate the complexity of the relationship between local and general structural measures.

Thalamic damage and long-term progression of disability in multiple sclerosis

PURPOSE

To estimate the relative contributions of baseline thalamic atrophy and abnormalities shown at magnetization transfer (MT) magnetic resonance (MR) imaging, as well as their 12-month changes, in predicting accumulation of disability in a relatively large sample of patients with relapse-onset multiple sclerosis (MS) during an 8-year period.

MATERIALS AND METHODS

The study was conducted with approval of the institutional review board. Written informed consent was obtained from each participant. Conventional and MT MR imaging of the brain was performed at baseline and at 12-month follow-up in 13 healthy control subjects and 73 patients with relapse-onset MS; participants were monitored with clinical visits for 8 years. The following parameters were evaluated at baseline and at 12-month follow-up: volume of lesions with high signal intensity at T2-weighted imaging, volume of lesions with low signal intensity at T1-weighted imaging, mean lesion MT ratio, thalamic fraction, and thalamic MT ratio. A multivariate analysis was used to evaluate the predictors of long-term neurologic deterioration.

RESULTS

At 8-year follow-up, 44 patients showed worsening disability. During follow-up, reduction in thalamic fraction was more pronounced in patients with relapsing-remitting MS than in those with secondary progressive MS (P = .001); thalamic MT ratio decreased only in patients with secondary progressive MS (P = .007). In the multivariable model, baseline thalamic fraction (odds ratio = 0.62, P = .01) and mean percentage change in lesion MT ratio after 12 months (odds ratio = 0.90, P = .04) were independent predictors of worsening disability at 8 years. At baseline, thalamic fraction was correlated with lesion volumes at T2-weighted imaging (r = -0.75, P < .001) and T1-weighted imaging (r = -0.60, P < .001).

CONCLUSION

Thalamic atrophy is correlated with long-term accumulation of disability in patients with MS. White matter lesions are likely to contribute to the loss of tissue seen in the thalamus of patients with MS.

Hippocampal atrophy in relapsing-remitting and primary progressive MS: a comparative study

Background: In multiple sclerosis (MS), demyelination and neuroaxonal damage are seen in the hippocampus, and MRI has revealed hippocampal atrophy.

Objectives: To investigate and compare hippocampal volume loss in patients with relapsing—remitting MS (RRMS) and primary progressive MS (PPMS) using manual volumetry, and explore its association with memory dysfunction.

Methods: Hippocampi were manually delineated on volumetric MRI of 34 patients with RRMS, 23 patients with PPMS and 18 controls. Patients underwent neuropsychological tests of verbal and visuospatial recall memory. Linear regression was used to compare hippocampal volumes between subject groups, and to assess the association with memory function.

Results: Hippocampal volumes were smaller in MS patients compared with controls, and were similar in patients with RRMS and PPMS. The mean decrease in hippocampal volume in MS patients was 317 mm3 (9.4%; 95% CI 86 to 549; p = 0.008) on the right and 284 mm3 (8.9%; 95% CI 61 to 508; p = 0.013) on the left. A borderline association of hippocampal volume with memory performance was observed only in patients with PPMS.

Conclusion: Hippocampal atrophy occurs in patients with RRMS and PPMS. Factors additional to hippocampal atrophy may impact on memory performance.

A comparative assessment of cerebral white matter by magnetization transfer imaging in early- and adult-onset multiple sclerosis patients matched for disease duration

A more favorable clinical course in early-onset (EO) multiple sclerosis (MS) than adult-onset (AO) disease is reported. Our aim was to assess white matter with/without lesions by magnetization transfer (MT) imaging in EO and AO MS patients matched for duration of the disease. Relapsing-remitting MS patients with disease onset at age < or =18 years and >18 years (n = 11 for each) were matched according to sex, age, disease duration, and 22 sex-and age-matched healthy subjects were studied with MT imaging. MT ratios (MTR) of manually outlined ROIs from T1-hypointense, T1-isointense lesions and perilesional normal appearing white matter (NAWM) as well as NAWM of the left frontal lobe of the patients and healthy subjects were calculated. MTR differences between two patient groups and control subjects, and correlation of MTR with EDSS, disease onset age, disease duration and relapse rate were analyzed statistically. In comparison with NAWM of the patients and healthy subjects, the greatest MTR reductions were observed in T1-hypointense lesions followed by T1-isointense lesions and perilesional NAWM, respectively, in EO and AO MS. Both groups' NAWM MTR were reduced; greater and more significantly in EO patients. No correlation was found between MTR of any ROI and EDSS, duration of the disease, disease onset age, or relapse rate. Although normalization does not occur, abnormality of white matter in MS decreases as distance from the lesions increases. Greater NAWM abnormality in EO MS may relate to inherent myelin abnormalities and different repair/reorganization processes in this particular group.

Early MRI in optic neuritis: the risk for clinically definite multiple sclerosis

MRI brain lesions at presentation with optic neuritis (ON) increase the risk for developing clinically definite (CD) multiple sclerosis (MS). More detailed early MRI findings may improve prediction of conversion.

The objectives of this study were to investigate the influence of number, location and activity of lesions at presentation, new lesions at early follow-up and non-lesion MRI measures on conversion from optic neuritis (ON) to CDMS.

142/143 ON patients, prospectively recruited into a serial MRI and clinical follow-up study, were followed-up at least once. Cox regression analysis determined independent early MRI predictors of time to CDMS from: (i) baseline lesion number, location and activity measures, (ii) three-month lesion activity measures and (iii) brain atrophy, magnetization transfer ratio and spectroscopy measures.

114/142 (80%) had abnormal baseline brain or cord MRI. 57 (40%) developed CDMS (median of 16 months from clinically isolated syndrome onset). Median follow-up of the non-converters was 62 months. Multivariate analysis of baseline parameters revealed gender, periventricular and gadolinium-enhancing lesions as independent predictors of CDMS. Considering both scans together, gender, baseline periventricular and new T2 lesions at follow-up remained significant (hazard ratios 2.1, 2.4 and 4.9, respectively). No non-conventional measure predicted CDMS.

It was concluded that new T2 lesions on an early follow-up scan were the strongest independent predictor of CDMS.

Bimonthly assessment of magnetization transfer magnetic resonance imaging parameters in multiple sclerosis: a 14-month, multicentre, follow-up study

This study was performed to assess the temporal evolution of damage within lesions and the normal-appearing white matter, measured using frequent magnetization transfer (MT) MRI, in relapsing-remitting multiple sclerosis (RRMS). The relationship of MT ratio (MTR) changes with measures of lesion burden, and the sample sizes needed to demonstrate a treatment effect on MTR metrics in placebo-controlled MS trials were also investigated. Bimonthly brain conventional and MT MRI scans were acquired from 42 patients with RRMS enrolled in the placebo arm of a 14-month, double-blind trial. Longitudinal MRI changes were evaluated using a random effect linear model accounting for repeated measures, and adjusted for centre effects. The Expanded Disability Status Scale (EDSS) score remained stable over the study period. A weak, but not statistically significant, decrease over time was detected for normal-appearing brain tissue (NABT) average MTR (-0.02% per visit; p = 0.14), and MTR peak height (-0.15 per visit; p = 0.17), while average lesion MTR showed a significant decrease over the study period (-0.07% per visit; p = 0.03). At each visit, all MTR variables were significantly correlated with T2 lesion volume (LV) (average coefficients of correlation ranging from -0.54 to -0.28, and p-values from <0.001 to 0.02). At each visit, NABT average MTR was also significantly correlated with T1-hypointense LV (average coefficient of correlation = -0.57, p < 0.001). The estimation of the sample sizes required to demonstrate a reduction of average lesion MTR (the only parameter with a significant decrease over the follow-up) ranged from 101 to 154 patients to detect a treatment effect of 50% in a 1-year trial with a power of 90%. The steady correlation observed between conventional and MT MRI measures over time supports the hypothesis of axonal degeneration of fibres passing through focal lesions as one of the factors contributing to the overall MS burden.

Magnetization transfer ratio abnormalities reflect clinically relevant grey matter damage in multiple sclerosis

BACKGROUND

In multiple sclerosis, grey matter (GM) damage appears more clinically relevant than either white matter damage or lesion load.

OBJECTIVE

We investigated if normal-appearing white matter (NAWM) and grey matter tissue changes assessed by magnetization transfer ratio were associated with long-term disability.

METHODS

Sixty-nine people were assessed 20 years after presentation with a clinically isolated syndrome (CIS) [28 still CIS, 31 relapsing-remitting multiple sclerosis, 10 secondary progressive multiple sclerosis], along with 19 healthy subjects. Mean magnetization transfer ratio, peak height (PH) and peak location of the normalized magnetization transfer ratio histograms were determined in NAWM and grey matter, as well as, white matter and GM Fraction (GMF) and T(2)-weighted lesion load.

RESULTS

Median expanded disability status scale for multiple sclerosis patients was 2.5 (range 1-8). GM-PH, and less so, NAWM mean and peak location, were lower in multiple sclerosis patients (P = 0.009) versus controls, relapsing-remitting multiple sclerosis versus CIS (P = 0.008) and secondary progressive multiple sclerosis versus relapsing-remitting multiple sclerosis (P = 0.002). GM-PH (as well as GMF) correlated with expanded disability status scale (r(s) = -0.49; P = 0.001) and multiple sclerosis functional score (r(s) = 0.51; P = 0.001). GM-PH independently predicted disability with similar strength to the associations of GMF with clinical measures.

CONCLUSION

Grey matter damage was related to long-term disability in multiple sclerosis cohort with a relatively low median expanded disability status scale. Markers of intrinsic grey matter damage (magnetization transfer ratio) and tissue loss offer clinically relevant information in multiple sclerosis.

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

Magnetization transfer imaging (MTI) provides a reliable and histopathologically validated means for identifying important tissue changes in multiple sclerosis (MS), including demyelination and remyelination. However, most approaches to date have been based on a priori regions of interest (ROIs) and have been relatively insensitive to small focal changes or competing processes. More recent techniques have sought to address this through a voxel-wise approach, but have been limited in their detection capabilities by the amount of noise in standard MTR images. To address this issue while remaining sensitive to local changes, we propose the use of the recently introduced threshold-free cluster enhancement (TFCE) technique in combination with a Monte Carlo estimation approach. TFCE is first applied to enhance individual voxels based on their level of local cluster support, and then Monte Carlo estimation is performed to allow meaningful statistical interpretation of the resulting TFCE values. We validated this technique in three complementary ways: healthy control scan-rescan analysis, analysis of a "gold standard" simulated dataset, and analysis of a group of MS patients and healthy volunteers with 1-year longitudinal MRI scans. Scan-rescan analysis demonstrated a very low false-positive rate (1.44 mL increasing and 1.48 mL decreasing at the optimal detection threshold). Simulated dataset analysis yielded an area under receiver-operating characteristic curve of 0.942 (compared to 0.801 for a more conventional voxel-wise thresholding analysis). Finally, analysis of the real subject population showed highly significant differences (p<0.001) in volume of decreasing MTR between patients and controls. The proposed method provides a valuable means for quantifying MS-related tissue changes, particularly demyelination and remyelination, in vivo and without the use of highly complex or experimental MRI acquisition techniques. It improves on the sensitivity of other approaches, and may increase the statistical power of studies investigating the effects of therapy on MRI outcomes in MS.

The definition of non-responder to multiple sclerosis treatment: neuroimaging markers

MRI is the main paraclinical tool used both to diagnose multiple sclerosis (MS) and to evaluate the efficacy of experimental treatments in phase II and III clinical trials. In the latter context, a major issue is represented by the weak correlations found between clinical and MRI aspects in the case of established MS, which are particularly evident when individual patients are considered. As a consequence, the definition of response to MS treatment, when based upon MRI aspects, remains a challenging task. Although the use of MRI-derived quantities to define treatment options and strategies at an individual patient level is supported by recent evidence, only the integration of clinical and MRI data can be considered a reliable approach for the work-up of patients undergoing disease-modifying treatments.

Clinical and conventional MRI predictors of disability and brain atrophy accumulation in RRMS. A large scale, short-term follow-up study

To assess the value of clinical and MRI variables in predicting short-term brain atrophy accumulation and clinical evolution in a large cohort of patients with RRMS, we studied a cohort of 548 patients, previously enrolled as a placebo arm of a 14-month, double-blind trial of oral glatiramer acetate (GA). A logistic regression model with EDSS progression as the dependent variable was built to assess baseline clinical and MRI variables associated with clinical worsening during follow-up. In 466 patients with complete central brain atrophy assessment, another linear regression model with percentage central brain volume change (PCBVC) as the dependent variable was built to assess baseline clinical and MRI variables associated with atrophy development.A total of 80 patients (15%) had EDSS progression over the follow-up period. Factors independently predicting the probability to have a clinical progression were lower EDSS (OR = 0.78, 95% CI = 0.62-0.97 p = 0.02) and higher T2 LL (OR = 1.022, 95% CI = 1.006-1.038, p = 0.007) at baseline. In the 466 patients with atrophy assessment, PCBVC declined, on average, by -2.0% (SD = 2.8) (p < 0.001) over the follow-up. The multivariate PCBVC analysis revealed that the PCBVC decrease was independently correlated with higher EDSS (p = 0.03) and T2 LL (p = 0.005) at baseline. The squared correlation coefficients of the composite scores made up of EDSS and T2 LL considered together were able to explain only 3 % of the variance in disability progression and only 4 % of the variance of PCBVC.In RRMS patients, clinical and conventional MRI findings at baseline only modestly predict shortterm accumulation of brain atrophy and disability. These data confirm the need to develop clinical and MRI measures more sensitive towards the more disabling aspects of the disease.

Magnetic resonance imaging metrics and their correlation with clinical outcomes in multiple sclerosis: a review of the literature and future perspectives

Magnetic resonance imaging (MRI) has revolutionized the diagnosis and management of patients with multiple sclerosis (MS). Conventional MRI metrics are employed as primary endpoints in proof-of-concept clinical trials evaluating new drugs for MS and as secondary endpoints in definitive phase III trials. Metrics derived from non-conventional MRI techniques are now emerging and hold significant promise since they appear to be more correlated with the most disabling features of MS. However, none of these has been approved for use as a surrogate endpoint for accumulation of physical disability, which is the most important clinical endpoint of this disease. Taking into account the large numbers of patients needed, the extensive exposure to placebo, and the relatively long duration required for phase III clinical trials to show a meaningful effect on progression of disability, the need for a valid, reliable, and objective paraclinical marker of disease evolution cannot be overemphasized. This paper reviews the most up-to-date data regarding MRI techniques, their relationship with central nervous system pathology, as well as with clinical endpoints, and proposes future insights into the use of MRI metrics as surrogate endpoints in clinical trials of MS.

Detecting treatment effects on brain atrophy in relapsing remitting multiple sclerosis: sample size estimates

Brain atrophy, thought to reflect neuroaxonal degeneration, may be considered an objective marker of disease progression in multiple sclerosis (MS). Our objective was to estimate sample sizes required for parallel group placebo-controlled trials of disease-modifying treatments in relapsing remitting MS (RRMS), using brain atrophy on MRI as the outcome measure. In addition, we investigated how brain atrophy measurement method and trial duration affect sample sizes. Thirty-three patients with RRMS and 16 controls had T1-weighted volumetric MR imaging acquired at baseline and up to six repeat time-points (six monthly intervals). Brain atrophy was quantified between baseline and each repeat image using four methods: segmented brain volume difference, BBSI, SIENA and ventricular enlargement. Linear mixed models were fitted to data from each subject group and method. Sample size calculations were performed using mean and variance estimates from these models. For a 2 year trial, a treatment slowing atrophy rate by 30% required 123 subjects in each treatment arm if using SIENA to measure atrophy, 157 for the BBSI, 140 for ventricular enlargement and 763 for segmented brain volume difference. For a given effect size and method, sample sizes were statistically significantly reduced the longer the trial duration. Our estimations suggest that brain atrophy could provide an additional outcome measure to clinical assessment for monitoring treatment effects in RRMS although the relationship between atrophy and subsequent disability, and potential confounding factors to atrophy measurement must be further investigated.

The place of MRI in monitoring the individual MS patient

Evidence of focal white matter inflammation on MRI can be related to relapses and chronic disability. The strength of the relationship depends on the stage of the disease. The predictive value is stronger early in the course of MS, when the focal white matter lesions are more important in the pathogenesis of MS. As the disease progresses, the predictive value of white matter lesions weakens and measures related to other, more diffuse aspects of the disease strengthen. Thus, lesion activity on MRI can be helpful as a guide to therapy, particularly early in the disease. Appropriate MRI criteria for a suboptimal response to therapy are not clear and may depend on the therapy being evaluated. The fact that diffuse pathology tends to progress despite effective suppression of focal inflammation is a cause for concern and needs to be addressed with new approaches to therapy that are more effective against this aspect of the disease.

Inflammatory demyelination and neurodegeneration in early multiple sclerosis

A number of recent magnetic resonance imaging studies have challenged the classical view of multiple sclerosis (MS) as a "two-stage" disease where an early inflammatory demyelinating phase with focal macroscopic lesions formed in the white matter (WM) of the central nervous system is followed by a late neurodegenerative phase, which is believed to be a mere consequence of repeated inflammatory insults and irreversible demyelination. These studies have consistently shown the presence of diffuse normal-appearing WM damage, marked gray matter involvement and significant cortical functional reorganization, as well as the occurrence of the neurodegenerative component of MS from the earliest clinical stages of the disease with only a partial relation to MRI markers of inflammatory demyelination. The present review argues that MS can no longer be viewed as a "two-stage" disease, which suggests that the two pathological components are dissociated in time, but rather as a "simultaneous two-component" disease, where the relative contributions of the various pathological processes of the disease to the development of "fixed" disability, their relationship and their evolution over time need to be clarified. This new view of MS should inform the development of future research protocols to define its actual physiopathology and prompt the institution of early treatment which should ideally target not only inflammatory demyelination, but also the neurodegenerative aspects of the disease, as well as promote neuroprotection and enhance reparative mechanisms and adaptive functional reorganization of the cortex.

[Future of non conventional MR techniques in MS]

Although conventional magnetic resonance imaging (MRI) is used for diagnosing multiple sclerosis (MS) and monitoring disease activity and course, the correlation between conventional MRI data and clinical findings remains weak. This "clinical-MRI paradox" could be partly due to the lack of MRI specificity related to the heterogeneous pathological substrates of MS and to its inability to quantify the extent of damage in the normal-appearing tissue. Recently, non-conventional MRI techniques, including magnetization transfer MRI, diffusion tensor MRI, and proton MR spectroscopy have been applied to improve our understanding of the pathophysiology of MS. These techniques may provide information about structural and biochemical changes occurring within and outside macroscopic MS lesions (inflammation, demyelination, axonal loss), in particular in the normal-appearing white and grey matter. These techniques could also significantly improve our ability to monitor inflammatory demyelination and axonal injury. In the same way, functional MRI gives us the potential substrate to assess the mechanisms of adaptive cortical reorganization, which may limit the irreversible consequences of MS tissue injury.

Magnetization transfer magnetic resonance imaging of the brain, spinal cord, and optic nerve

Magnetic resonance imaging is highly sensitive in revealing CNS abnormalities associated with several neurological conditions, but lacks specificity for their pathological substrates. In addition, MRI does not allow evaluation of the presence and extent of damage in regions that appear normal on conventional MRI sequences and that postmortem studies have shown to be affected by pathology. Quantitative MR-based techniques with increased pathological specificity to the heterogeneous substrates of CNS pathology have the potential to overcome such limitations. Among these techniques, one of the most extensively used for the assessment of CNS disorders is magnetization transfer MRI (MT-MRI). The application of this technique for the assessment of damage in macroscopic lesions, in normal-appearing white and gray matter, and in the spinal cord and optic nerve of patients with several neurological conditions is providing important in vivo information-dramatically improving our understanding of the factors associated with the appearance of clinical symptoms and the accumulation of irreversible disability. MT-MRI also has the potential to contribute to the diagnostic evaluation of several neurological conditions and to improve our ability to monitor treatment efficacy in experimental trials.

Magnetization Transfer MRI in Multiple Sclerosis

In multiple sclerosis (MS), conventional magnetic resonance imaging (cMRI) has proved to be sensitive for detecting lesions and their changes over time. However, cMRI is not able to characterize and quantify the tissue damage within and outside such lesions. Magnetization transfer (MT) MRI is a quantitative technique with the potential to overcome this limitation and, as a consequence, to provide additional information about the nature and the extent of tissue damage associated to this disease. During the last 10 years, MT MRI indeed has allowed us to quantify the structural changes occurring within and outside lesions visible on cMRI scans, thus providing a more accurate in vivo picture of the heterogeneity of MS and, as a consequence, improving our ability to monitor the evolution of the disease. The application of MT MRI to the study of MS has contributed to change our understanding of how MS causes irreversible disability by showing that MS is more than an inflammatory-demyelinating condition of the white matter of the central nervous system.