Improved identification of intracortical lesions in multiple sclerosis with phase-sensitive inversion recovery in combination with fast double inversion recovery MR imaging

Recommendations to improve imaging and analysis of brain lesion load and atrophy in longitudinal studies of multiple sclerosis

Focal lesions and brain atrophy are the most extensively studied aspects of multiple sclerosis (MS), but the image acquisition and analysis techniques used can be further improved, especially those for studying within-patient changes of lesion load and atrophy longitudinally. Improved accuracy and sensitivity will reduce the numbers of patients required to detect a given treatment effect in a trial, and ultimately, will allow reliable characterization of individual patients for personalized treatment. Based on open issues in the field of MS research, and the current state of the art in magnetic resonance image analysis methods for assessing brain lesion load and atrophy, this paper makes recommendations to improve these measures for longitudinal studies of MS. Briefly, they are (1) images should be acquired using 3D pulse sequences, with near-isotropic spatial resolution and multiple image contrasts to allow more comprehensive analyses of lesion load and atrophy, across timepoints. Image artifacts need special attention given their effects on image analysis results. (2) Automated image segmentation methods integrating the assessment of lesion load and atrophy are desirable. (3) A standard dataset with benchmark results should be set up to facilitate development, calibration, and objective evaluation of image analysis methods for MS.

Regional cortical thickness in relapsing remitting multiple sclerosis: A multi-center study

A comprehensive analysis of the global and regional values of cortical thickness based on 3D magnetic resonance images was performed on 250 relapsing remitting multiple sclerosis (MS) patients who participated in a multi-center, randomized, phase III clinical trial (the CombiRx Trial) and 125 normal controls. The MS cohort was characterized by relatively low clinical disability and short disease duration. An automatic pipeline was developed for identifying images with poor quality and artifacts. The global and regional cortical thicknesses were determined using FreeSurfer software. Our results indicate significant cortical thinning in multiple regions in the MS patient cohort relative to the controls. Both global cortical thinning and regional cortical thinning were more prominent in the left hemisphere relative to the right hemisphere. Modest correlation was observed between cortical thickness and clinical measures that included the extended disability status scale and disease duration. Modest correlation was also observed between cortical thickness and T1-hypointense and T2-hyperintense lesions. These correlations were very similar at 1.5 T and 3 T field strengths. A much weaker inverse correlation between cortical thickness and age was observed among the MS subjects compared to normal controls. This age-dependent correlation was also stronger in males than in females. The values of cortical thickness were very similar at 1.5 T and 3 T field strengths. However, the age-dependent changes in both global and regional cortical thicknesses were observed to be stronger at 3 T relative to 1.5 T.

Quantitative magnetic resonance imaging of cortical multiple sclerosis pathology

Although significant improvements have been made regarding the visualization and characterization of cortical multiple sclerosis (MS) lesions using magnetic resonance imaging (MRI), cortical lesions (CL) continue to be under-detected in vivo, and we have a limited understanding of the causes of GM pathology. The objective of this study was to characterize the MRI signature of CLs to help interpret the changes seen in vivo and elucidate the factors limiting their visualization. A quantitative 3D high-resolution (350 μm isotropic) MRI study at 3 Tesla of a fixed post mortem cerebral hemisphere from a patient with MS is presented in combination with matched immunohistochemistry. Type III subpial lesions are characterized by an increase in T1, T2 and M0, and a decrease in MTR in comparison to the normal appearing cortex (NAC). All quantitative MR parameters were associated with cortical GM myelin content, while T1 showed the strongest correlation. The histogram analysis showed extensive overlap between CL and NAC for all MR parameters and myelin content. This is due to the poor contrast in myelin content between CL and NAC in comparison to the variability in myelo-architecture throughout the healthy cortex. This latter comparison is highlighted by the representation of T1 times on cortical surfaces at several laminar depths.

Shifting imaging targets in multiple sclerosis: from inflammation to neurodegeneration

Classically multiple sclerosis (MS) has been regarded as an auto-immune disease of the white matter in the central nervous system leading to severe disability over the course of several decades. Current therapeutic strategies in MS are mostly based on either immune suppression or immune modulation. Although effective in decreasing relapse frequency and severity as well as delaying disease progression, MS pathology ensues nonetheless. In the last decade it became evident that gray matter pathology plays an important role in disease progression and helps explaining certain aspects of MS-related disability such as cognitive decline. Conventional MRI outcome measures commonly used in clinical trials are sufficient to demonstrate an anti-inflammatory drug-effect but lack pathological specificity and are poor to moderate predictors of disability. In this article, we review new insights in gray matter pathology and functional reorganization in MS and how these novel fields in MS research may validate and establish new MRI outcome measures, aid in the development of new therapeutic strategies for neuroprotection and neurorepair, and may lead to development of novel predictive measures of disability and disease progression in MS.

Grey matter lesions in MS: from histology to clinical implications

Although multiple sclerosis (MS) is a chronic inflammatory-demyelinating disease of the white matter (WM) of the central nervous system, several pathological and magnetic resonance imaging (MRI) studies have shown that a large amount of lesions are located in the cortical and deep gray matter. The histopathological and immunological characteristics of cortical lesions differ significantly from those located in the WM, which suggests a location-dependent expression of the MS immunopathological process. More recently, the availability of not-conventional MRI sequences having higher sensitivity for the gray matter has allowed to depict in vivo a portion of such lesions. The available MRI data obtained on large cohorts of patients, having different clinical forms of the disease, indicate that cortical lesions can be detected early in the disease course, sometimes even before the appearance of WM lesions, and correlate with the severity of physical disability and cognitive impairment, and with the evolution of the disease toward the secondary progressive phase. This review provides a summary of the main histopathological and MRI findings of cortical lesions in MS and discusses their possible clinical implications.

Detecting cortical lesions in multiple sclerosis at 7 T using white matter signal attenuation

Cortical lesions have recently been a focus of multiple sclerosis (MS) MR research. In this study, we present a white matter signal attenuating sequence optimized for cortical lesion detection at 7 T. The feasibility of white matter attenuation (WHAT) for cortical lesion detection was determined by scanning eight patients (four relapsing/remitting MS, four secondary progressive MS) at 7 T. WHAT showed excellent gray matter-white matter contrast, and cortical lesions were hyperintense to the surrounding cortical gray matter, The sequence was then optimized for cortical lesion detection by determining the set of sequence parameters that produced the best gray matter-cortical lesion contrast in a 10-min scan. Despite the B1 inhomogeneities common at ultra-high field strengths, WHAT with an adiabatic inversion pulse showed good cortical lesion detection and would be a valuable component of clinical MS imaging protocols.

Clinical correlates of grey matter pathology in multiple sclerosis

Traditionally, multiple sclerosis has been viewed as a disease predominantly affecting white matter. However, this view has lately been subject to numerous changes, as new evidence of anatomical and histological changes as well as of molecular targets within the grey matter has arisen. This advance was driven mainly by novel imaging techniques, however, these have not yet been implemented in routine clinical practice. The changes in the grey matter are related to physical and cognitive disability seen in individuals with multiple sclerosis. Furthermore, damage to several grey matter structures can be associated with impairment of specific functions. Therefore, we conclude that grey matter damage - global and regional - has the potential to become a marker of disease activity, complementary to the currently used magnetic resonance markers (global brain atrophy and T2 hyperintense lesions). Furthermore, it may improve the prediction of the future disease course and response to therapy in individual patients and may also become a reliable additional surrogate marker of treatment effect.

Assessing abnormal iron content in the deep gray matter of patients with multiple sclerosis versus healthy controls

BACKGROUND AND PURPOSE

It is well known that patients with MS tend to have abnormal iron deposition in and around the MS plaques, in the basal ganglia and the THA. In this study, we used SWI to quantify iron content in patients with MS and healthy volunteers.

MATERIALS AND METHODS

Fifty-two patients with MS were recruited to assess abnormal iron content in their basal ganglia and THA structures. One hundred twenty-two healthy subjects were recruited to establish a baseline of normal iron content in deep GM structures. Each structure was separated into 2 regions: a low-iron-content region and a high-iron-content region. The average phase, the percentage area, and the total phase of the high-iron-content region were evaluated. A weighting was also assigned to each subject depending on the level of iron content and its deviation from the normal range.

RESULTS

A clear separation between iron content in healthy subjects versus patients with MS was seen. For healthy subjects 13% and for patients with MS 65% showed an iron-weighting factor >3 SDs from the normal mean (P < .05). The results for those patients younger than 40 years are even more impressive. In these cases, only 1% of healthy subjects and 67% of patients with RRMS showed abnormally high iron content.

CONCLUSIONS

Iron-weighting factors in the basal ganglia, THA, and the midbrain appeared to be abnormal in roughly two-thirds of patients with MS as measured by SWI.

Gray matter imaging in multiple sclerosis: what have we learned?

At the early onset of the 20^th century, several studies already reported that the gray matter was implicated in the histopathology of multiple sclerosis (MS). However, as white matter pathology long received predominant attention in this disease, and histological staining techniques for detecting myelin in the gray matter were suboptimal, it was not until the beginning of the 21^st century that the true extent and importance of gray matter pathology in MS was finally recognized. Gray matter damage was shown to be frequent and extensive, and more pronounced in the progressive disease phases. Several studies subsequently demonstrated that the histopathology of gray matter lesions differs from that of white matter lesions. Unfortunately, imaging of pathology in gray matter structures proved to be difficult, especially when using conventional magnetic resonance imaging (MRI) techniques. However, with the recent introduction of several more advanced MRI techniques, the detection of cortical and subcortical damage in MS has considerably improved. This has important consequences for studying the clinical correlates of gray matter damage. In this review, we provide an overview of what has been learned about imaging of gray matter damage in MS, and offer a brief perspective with regards to future developments in this field.

Intracortical lesions by 3T magnetic resonance imaging and correlation with cognitive impairment in multiple sclerosis

BACKGROUND

Accurate classification of multiple sclerosis (MS) lesions in the brain cortex may be important in understanding their impact on cognitive impairment (CI). Improved accuracy in identification/classification of cortical lesions was demonstrated in a study combining two magnetic resonance imaging (MRI) sequences: double inversion recovery (DIR) and T1-weighted phase-sensitive inversion recovery (PSIR).

OBJECTIVE

To evaluate the role of intracortical lesions (IC) in MS-related CI and compare it with the role of mixed (MX), juxtacortical (JX), the sum of IC + MX and with total lesions as detected on DIR/PSIR images. Correlations between CI and brain atrophy, disease severity and disease duration were also sought.

METHODS

A total of 39 patients underwent extensive neuropsychological testing and were classified into normal and impaired groups. Images were obtained on a 3T scanner and cortical lesions were assessed blind to the cognitive status of the subjects.

RESULTS

Some 238 cortical lesions were identified (130 IC, 108 MX) in 82% of the patients; 39 JX lesions were also identified. Correlations between CI and MX lesions alone (p = 0.010) and with the sum of IC + MX lesions (p = 0.030) were found. A correlation between severity of CI and Expanded Disability Status Scale was also seen (p = 0.009).

CONCLUSION

Cortical lesions play an important role in CI. However, our results suggest that lesions that remain contained within the cortical ribbon do not play a more important role than ones extending into the adjacent white matter; furthermore, the size of the cortical lesion, and not the tissue-specific location, may better explain their correlation with CI.

Optimization of a double inversion recovery sequence for noninvasive synovium imaging of joint effusion in the knee

PURPOSE

We wanted to optimize a double inversion recovery (DIR) sequence to image joint effusion regions of the knee, especially intracapsular or intrasynovial imaging in the suprapatellar bursa and patellofemoral joint space.

METHODS

Computer simulations were performed to determine the optimum inversion times (TI) for suppressing both fat and water signals, and a DIR sequence was optimized based on the simulations for distinguishing synovitis from fluid. In vivo studies were also performed on individuals who showed joint effusion on routine knee MR images to demonstrate the feasibility of using the DIR sequence with a 3T whole-body MR scanner. To compare intracapsular or intrasynovial signals on the DIR images, intermediate density-weighted images and/or post-enhanced T1-weighted images were acquired.

RESULTS

The timings to enhance the synovial contrast from the fluid components were TI1 = 2830 ms and TI2 = 254 ms for suppressing the water and fat signals, respectively. Improved contrast for the intrasynovial area in the knees was observed with the DIR turbo spin-echo pulse sequence compared to the intermediate density-weighted sequence.

CONCLUSIONS

Imaging contrast obtained noninvasively with the DIR sequence was similar to that of the post-enhanced T1-weighted sequence. The DIR sequence may be useful for delineating synovium without using contrast materials.

MR imaging of multiple sclerosis

Owing to its ability to depict the pathologic features of multiple sclerosis (MS) in exquisite detail, conventional magnetic resonance (MR) imaging has become an established tool in the diagnosis of this disease and in monitoring its evolution. MR imaging has been formally included in the diagnostic work-up of patients who present with a clinically isolated syndrome suggestive of MS, and ad hoc diagnostic criteria have been proposed and are updated on a regular basis. In patients with established MS and in those participating in treatment trials, examinations performed with conventional MR pulse sequences provide objective measures to monitor disease activity and progression; however, they have a limited prognostic role. This has driven the application of newer MR imaging technologies, including higher-field-strength MR units, to estimate overall MS burden and mechanisms of recovery in patients at different stages of the disease. These techniques have allowed in vivo assessment of the heterogeneity of MS pathologic features in focal lesions and in normal-appearing tissues. More recently, some of the finer details of MS, including macrophage infiltration and abnormal iron deposition, have become quantifiable with MR imaging. The utility of these modern MR techniques in clinical trial monitoring and in the assessment of the individual patient's response to treatment still need to be evaluated.

Trimmed-likelihood estimation for focal lesions and tissue segmentation in multisequence MRI for multiple sclerosis

We present a new automatic method for segmentation of multiple sclerosis (MS) lesions in magnetic resonance images. The method performs tissue classification using a model of intensities of the normal appearing brain tissues. In order to estimate the model, a trimmed likelihood estimator is initialized with a hierarchical random approach in order to be robust to MS lesions and other outliers present in real images. The algorithm is first evaluated with simulated images to assess the importance of the robust estimator in presence of outliers. The method is then validated using clinical data in which MS lesions were delineated manually by several experts. Our method obtains an average Dice similarity coefficient (DSC) of 0.65, which is close to the average DSC obtained by raters (0.66).

Progressive multiple sclerosis and gray matter pathology: an MRI perspective

The evidence suggesting a role of extensive cortical demyelization and atrophy in progressive multiple sclerosis is rapidly increasing. Although conventional magnetic resonance imaging has had a huge impact on multiple sclerosis by enabling an earlier diagnosis, and by providing surrogate markers for monitoring disease response to anti-inflammatory/immunomodulatory treatments, it is limited by the low pathological specificity and the low sensitivity to both diffuse damage in normal-appearing white matter and focal and diffuse damage in gray matter. Advanced magnetic resonance imaging techniques can partially overcome these limitations by providing markers more specific to the underlying pathologic substrates and more sensitive to the structural and functional "occult" brain tissue damage in patients with multiple sclerosis. This review describes brain and spinal cord imaging studies of multiple sclerosis with particular emphasis on gray matter imaging in both secondary progressive and primary progressive multiple sclerosis, discusses the clinical implications of gray matter damage, and outlines current magnetic resonance imaging developments at high and ultrahigh magnetic field strength.

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.

Examination of the role of magnetic resonance imaging in multiple sclerosis: A problem-orientated approach

Magnetic Resonance Imaging (MRI) has brought in several benefits to the study of Multiple Sclerosis (MS). It provides accurate measurement of disease activity, facilitates precise diagnosis, and aid in the assessment of newer therapies. The imaging guidelines for MS are broadly divided in to approaches for imaging patients with suspected MS or clinically isolated syndromes (CIS) or for monitoring patients with established MS. In this review, the technical aspects of MR imaging for MS are briefly discussed. The imaging process need to capture the twin aspects of acute MS viz. the autoimmune acute inflammatory process and the neurodegenerative process. Gadolinium enhanced MRI can identify acute inflammatory lesions precisely. The commonly applied MRI marker of disease progression is brain atrophy. Whole brain magnetization Transfer Ratio (MTR) and Magnetic Resonance Spectroscopy (MRS) are two other techniques use to monitor disease progression. A variety of imaging techniques such as Double Inversion Recovery (DIR), Spoiled Gradient Recalled (SPGR) acquisition, and Fluid Attenuated Inversion Recovery (FLAIR) have been utilized to study the cortical changes in MS. MRI is now extensively used in the Phase I, II and III clinical trials of new therapies. As the technical aspects of MRI advance rapidly, and higher field strengths become available, it is hoped that the impact of MRI on our understanding of MS will be even more profound in the next decade.

Diagnostic criteria for multiple sclerosis: 2010 revisions to the McDonald criteria

New evidence and consensus has led to further revision of the McDonald Criteria for diagnosis of multiple sclerosis. The use of imaging for demonstration of dissemination of central nervous system lesions in space and time has been simplified, and in some circumstances dissemination in space and time can be established by a single scan. These revisions simplify the Criteria, preserve their diagnostic sensitivity and specificity, address their applicability across populations, and may allow earlier diagnosis and more uniform and widespread use.

Identification and clinical impact of multiple sclerosis cortical lesions as assessed by routine 3T MR imaging

BACKGROUND AND PURPOSE

Histopathologic studies have reported widespread cortical lesions in MS; however, in vivo detection by using routinely available pulse sequences is challenging. We investigated the relative frequency and subtypes of cortical lesions and their relationships to white matter lesions and cognitive and physical disability.

MATERIALS AND METHODS

Cortical lesions were identified and classified on the basis of concurrent review of 3D FLAIR and 3D T1-weighted IR-SPGR 3T MR images in 26 patients with MS. Twenty-five patients completed the MACFIMS battery. White matter lesion volume, cortical lesion number, and cortical lesion volume were assessed.

RESULTS

Overall, 249 cortical lesions were detected. Cortical lesions were present in 24/26 patients (92.3%) (range per patient, 0-30; mean, 9.6 ± 8.8). Most (94.4%, n = 235) cortical lesions were classified as mixed cortical-subcortical (type I); the remaining 5.6% (n = 14) were classified as purely intracortical (type II). Subpial cortical lesions (type III) were not detected. White matter lesion volume correlated with cortical lesion number and cortical lesion volume (r(S) = 0.652, r(S) = 0.705, respectively; both P < .001). After controlling for age, depression, and premorbid intelligence, we found that all MR imaging variables (cortical lesion number, cortical lesion volume, white matter lesion volume) correlated with the SDMT score (R(2) = 0.513, R(2) = 0.449, R(2) = 0.418, respectively; P < .014); cortical lesion number also correlated with the CVLT-II scores (R(2) = 0.542-0.461, P < .043). The EDSS scores correlated with cortical lesion number and cortical lesion volume (r(S) = 0.472, r(S) = 0.404, respectively; P < .05), but not with white matter lesion volume.

CONCLUSIONS

Our routinely available imaging method detected many cortical lesions in patients with MS and was useful in their precise topographic characterization in the context of the gray matter-white matter junction. Routinely detectable cortical lesions were related to physical disability and cognitive impairment.

3 Tesla and 7 Tesla MRI of multiple sclerosis cortical lesions

Cortical lesions are prevalent in multiple sclerosis but are poorly detected using MRI. The double inversion recovery (DIR) sequence is increasingly used to explore the clinical relevance of cortical demyelination. Here we evaluate the agreement between imaging sequences at 3 Tesla (T) and 7T for the presence and appearance of individual multiple sclerosis cortical lesions. Eleven patients with demyelinating disease and eight healthy volunteers underwent MR imaging at 3T (fluid attenuated inversion recovery [FLAIR], DIR, and T(1)-weighted magnetization prepared rapid acquisition gradient echo [MP-RAGE] sequences) and 7T (T(1)-weighted MP-RAGE). There was good agreement between images for the presence of mixed cortical lesions (involving both gray and white matter). However, agreement between imaging sequences was less good for purely intracortical lesions. Even after retrospective analysis, 25% of cortical lesions could only be visualized on a single MRI sequence. Several DIR hyperintensities thought to represent cortical lesions were found to correspond to signal arising from extracortical blood vessels. High-resolution 7T imaging appeared useful for confidently classifying the location of lesions in relation to the cortical/subcortical boundary. We conclude that DIR, FLAIR, and MP-RAGE imaging sequences appear to provide complementary information during the detection of multiple sclerosis cortical lesions. High resolution 7T imaging may facilitate anatomical localization of lesions in relation to the cortical boundary.

Composite MRI scores improve correlation with EDSS in multiple sclerosis

BACKGROUND

Quantitative measures derived from magnetic resonance imaging (MRI) have been widely investigated as non-invasive biomarkers in multiple sclerosis (MS). However, the correlation of single measures with Expanded Disability Status Scale (EDSS) is poor, especially for studies with large population samples.

OBJECTIVE

To explore the correlation of MRI-derived measures with EDSS through composite MRI scores.

METHODS

Magnetic resonance images of 126 patients with relapsing-remitting MS were segmented into white and gray matter, cerebrospinal fluid, T2-hyperintense lesions, gadolinium contrast-enhancing lesions, T1-hypointense lesions ('black holes': BH). The volumes and average T2 values for each of these tissues and lesions were calculated and converted to a z-score (in units of standard deviation from the mean). These z-scores were combined to construct composite z-scores, and evaluated against individual z-scores for correlation with EDSS.

RESULTS

Composite scores including relaxation times of different tissues and/or volumetric measures generally correlated more strongly with EDSS than individual measures. The maximum observed correlation of a composite with EDSS was r = 0.344 (p < 0.0001), which is an improvement over the highest-performing single MRI measure (BH; r = 0.298, p < 0.001).

CONCLUSION

Z-transformation permits construction of composite scores including volumetric and T2-relaxation measures. Inclusion of multiple MRI measures in the composite can provide a broader characterization of the disease process, resulting in more robust correlations with EDSS.

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.

T1 cortical hypointensities and their association with cognitive disability in multiple sclerosis

Background: Neocortical lesions (NLs) largely contribute to the pathology of multiple sclerosis (MS), although their relevance in patients’ disability remains unknown.

Objective: To assess the incidence of T1 hypointense NLs by 3.0-Tesla magnetic resonance imaging (MRI) in patients with MS and examine neocortical lesion association with cognitive impairment.

Methods: In this case-control study, 21 MS patients and 21 age-, sex- and years of education-matched healthy volunteers underwent: (i) a neuropsychological examination rating cognitive impairment (Minimal Assessment of Cognitive Function in MS); (ii) a 3.0-Tesla MRI inclusive of an isotropic 1.0 mm3 three-dimensional inversion prepared spoiled gradient-recalled-echo (3D-IRSPGR) image and T1- and T2-weighted images. Hypointensities on 3D-IRSPGR lying in the cortex, either entirely or partially were counted and association between NLs and cognitive impairment investigated.

Results: A total of 95 NLs were observed in 14 (66.7%) patients. NL+ patients performed poorer (p = 0.020) than NLpatients only on the delayed recall component of the California Verbal Learning Test. This difference lost statistical significance when a correction for white matter lesion volume was employed.

Conclusions: Although T 1 hypointense NLs may be present in a relatively high proportion of multiple sclerosis patients, the impact that they have in cognitive impairment is not independent from white matter disease.

Novel MRI approaches to assess patients with multiple sclerosis

PURPOSE OF REVIEW

This review summarizes novel MRI approaches for the investigation of lesion burden and understanding of the pathophysiology of multiple sclerosis (MS).

RECENT FINDINGS

Recent technical advances are improving our ability to detect and define the nature of focal lesions and 'diffuse' tissue damage in MS as well as the functional consequences of such structural abnormalities. New contrast agents allow to monitor the pluriformity of MS inflammation. Double inversion recovery sequences enable us to detect and monitor the evolution of MS lesions in the cortex. High and ultra-high field scanners are improving imaging of MS-related abnormalities at an unprecedented resolution. Furthermore, this new generation of scanners has the potential to ameliorate structural and functional MR studies of the disease. All of this has contributed, and is likely to continue to contribute, to the definition of the factors associated with the development of irreversible disability in MS. Finally, new analysis methods have allowed to track regional disease-related changes and are resulting in an increased correlation between MRI and clinical deficits.

SUMMARY

Novel MR approaches highlighted previously unrecognized or neglected aspects of MS pathophysiology, which are likely to improve our understanding of the heterogeneous clinical manifestations of this condition.

Double inversion recovery: impact of incidental magnetic transfer effects on optimal inversion times

OBJECTIVES

Doube inversion recovery (DIR) is increasingly used in clinical studies on multiple sclerosis, as it selectively images gray matter and lesions. The inversion times used in literature differ significantly from theoretical predictions. One explanation for this are incidental magnetic transfer (iMT) effects, which are caused by the high density of pulses. In this work, the influence of iMT on DIR was analyzed and compared with theoretical assumptions and inversion times found in literature.

MATERIALS AND METHODS

Three subjects were measured with 2D DIR sequences. The number of slices measured was varied. Optimum inversion times for white matter (WM) suppression were determined for 1 and for 24 slices by increasing TI2. The impact of slice-to-slice cross talk was evaluated with phantom measurements.

RESULTS

For constant inversion times TI1 = 3400 ms and TI2 = 325 ms signal intensity of WM decreased with increasing number of slices. The effective longitudinal relaxation time T1sat of WM was with 24 slices (strong iMT effect) 28% lower than at 1 slice (almost no iMT effect). The determined T1sat for 24 slices was 540 ms, compared with 750 ms with 1 slice.

CONCLUSIONS

Incidental magnetic transfer effects have a huge impact on 2D DIR sequences. The number of slices measured affect strongly the severity of the iMT effect. This can lead to a strong decrease of T1sat for WM depending on the interleaving scheme. Results from different studies and at different field strengths are therefore not easily comparable, without exact knowledge of the sequence design.

Examination of the role of MRI in multiple sclerosis: a problem orientated approach

Current multiple sclerosis (MS) is generally thought to consist of two general pathological processes; acute inflammation and degeneration. The relationship between these two components is not understood. What is clear, however, is that the measures of acute inflammation are a poor predictor of long-term disability. Although some have suggested that inflammation may not contribute directly to the essential pathology in MS or that it is secondary to tissue degeneration, most students of the disease believe that the two processes are linked. Therefore, applications of MRI to measure both components of the disease are important. As most readers know, considerable success has been achieved in measuring acute inflammation and very little success has been obtained in identifying measures that correlate with disability and the prediction of future disability has not been achieved. In this review, we will examine the successes and failures of MRI in measuring these two components of the disease process. Consequently, we will not attempt to provide a detailed review of each MRI technique or sequence that has been applied to MS (a number of excellent reviews are available) but rather discuss how these techniques have been applied to answer specific questions. We will provide some comments on the use of MRI in clinical trials as well as in clinical practice. Finally, we will end with a brief discussion of future challenges.

Quantitative cervical spinal cord 3T proton MR spectroscopy in multiple sclerosis

BACKGROUND AND PURPOSE

Brain proton MR spectroscopy ((1)H-MR spectroscopy) is a useful technique for evaluating neuronal/axonal damage and demyelization in multiple sclerosis (MS). Because MS disability is frequently related to spinal cord lesions, potential markers for MS stage differentiation and severity would require in vivo quantification of spinal integrity. However, few spectroscopy studies have investigated cervical disease due to technical difficulties. The present study used 3T (1)H-MR spectroscopy to measure the main metabolites in cervical spinal cord plaques of a group in patients with relapsing-remitting MS (RRMS) and compared them with metabolite measurements in healthy volunteers.

MATERIALS AND METHODS

A (1)H-MR point-resolved spectroscopy sequence volume of interest was prescribed along the main axis of the cord between C2 and C3 levels on a plaque in a group of 15 patients with RRMS for a total acquisition time of approximately 14 minutes. MR spectroscopy data were analyzed by the user-independent fitting routine LCModel, and relative metabolite concentrations were expressed by the absolute concentration ratios. A Student t test was used to evaluate the difference compared with the healthy metabolite content previously published.

RESULTS

We found a significant decrease of total N-acetylaspartate/choline and an increase in choline/creatine and myo-inositol/creatine content on MS plaques in comparison with healthy cervical spine tissue.

CONCLUSIONS

In vivo (1)H-MR spectroscopy, if confirmed by other similar studies, should be as reliable for clinical studies as it is in brain imaging. Moreover, (1)H-MR spectroscopy allows examination of spinal cord integrity at a biochemical level and may be sensitive to subtle changes occurring during the course of MS disease.

MR imaging of gray matter involvement in multiple sclerosis: implications for understanding disease pathophysiology and monitoring treatment efficacy

Recent pathologic and MR imaging studies have challenged the classic view of MS as a chronic inflammatory-demyelinating condition affecting solely the WM of the central nervous system. Indeed, an involvement of the GM has been shown to occur from the early stages of the disease, to progress with time, and to be only moderately correlated with the extent of WM injury. In this review, we summarize how advances in MR imaging technology and methods of analysis are contributing to ameliorating the detection of focal lesions and to quantifying the extent of "occult" pathology and atrophy, as well as to defining the topographic distribution of such changes in the GM of patients with MS. These advances, combined with the imaging of brain reorganization occurring after tissue injury, should ultimately result in an improved understanding and monitoring of MS clinical manifestations and evolution, either natural or modified by treatment.

Multiple sclerosis with predominant, severe cognitive impairment

OBJECTIVE

To describe the characteristics of multiple sclerosis (MS) presenting with severe cognitive impairment as its primary disabling manifestation.

DESIGN

Retrospective case series.

SETTING

Tertiary referral center. Patients Patients were identified through the Mayo Clinic data retrieval system (1996-2008) with definite MS (McDonald criteria) and severe cognitive impairment as their primary neurological symptom without accompanying significant MS-related impairment or alternative diagnosis for cognitive dysfunction. Twenty-three patients meeting inclusion criteria were compared regarding demographics, clinical course, and radiological features.

MAIN OUTCOME MEASURES

Demographic, clinical, and radiological characteristics of the disease.

RESULTS

Twelve patients were men. The median age of the first clinical symptom suggestive of central nervous system demyelination was 33 years, and severe MS-related cognitive impairment developed at a median age of 39 years. Cognitive impairment could be dichotomized as subacute fulminant (n = 9) or chronic progressive (n = 14) in presentation, which corresponded to subsequent relapsing or progressive MS courses. Study patients commonly exhibited psychiatric (65%), mild cerebellar (57%), and cortical symptoms and signs (eg, seizure, aphasia, apraxia) (39%). Fourteen of 21 (67%), where documented, smoked cigarettes. Brain magnetic resonance imaging demonstrated diffuse cerebral atrophy in 16 and gadolinium-enhancing lesions in 11. Asymptomatic spinal cord magnetic resonance imaging lesions were present in 12 of 16 patients (75%). Immunomodulatory therapies were generally ineffective in improving these patients.

CONCLUSIONS

We describe patients with MS whose clinical phenotype is characterized by severe cognitive dysfunction and prominent cortical and psychiatric signs presenting as a subacute fulminant or chronic progressive clinical course. Cigarette smokers may be overrepresented in this phenotype.

In vivo imaging of cortical pathology in multiple sclerosis using ultra-high field MRI

OBJECTIVE

We used ultra-high field MRI to visualize cortical lesion types described by neuropathology in 16 patients with multiple sclerosis (MS) compared with 8 age-matched controls; to characterize the contrast properties of cortical lesions including T2*, T2, T1, and phase images; and to investigate the relationship between cortical lesion types and clinical data.

METHODS

We collected, on a 7-T scanner, 2-dimensional fast low-angle shot (FLASH)-T2*-weighted spoiled gradient-echo, T2-weighted turbo spin-echo (TSE) images (0.33 x 033 x 1 mm(3)), and a 3-dimensional magnetization-prepared rapid gradient echo.

RESULTS

Overall, 199 cortical lesions were detected in patients on both FLASH-T2* and T2-TSE scans. Seven-tesla MRI allowed for characterization of cortical plaques into type I (leukocortical), type II (intracortical), and type III/IV (subpial extending partly or completely through the cortical width) lesions as described histopathologically. Types III and IV were the most frequent type of cortical plaques (50.2%), followed by type I (36.2%) and type II (13.6%) lesions. Each lesion type was more frequent in secondary progressive than in relapsing-remitting MS. This difference, however, was significant only for type III/IV lesions. T2*-weighted images showed the highest, while phase images showed the lowest, contrast-to-noise ratio for all cortical lesion types. In patients, the number of type III/IV lesions was associated with greater disability (p < 0.02 by Spearman test) and older age (p < 0.04 by Spearman test).

CONCLUSIONS

Seven-tesla MRI detected different histologic cortical lesion types in our small multiple sclerosis (MS) sample, suggesting, if validated in a larger population, that it may prove a valuable tool to assess the contribution of cortical MS pathology to clinical disability.

[Magnetic resonance imaging of central nervous system inflammation]

Magnetic resonance imaging (MRI) is widely used to explore central nervous system inflammatory disorders, especially multiple sclerosis (MS). Advanced MRI methods are bringing more sensitive and specific tools for each step of the inflammatory process. In this review, we discuss the different MRI approaches for inflammatory disorders exploration, especially MS. We give particular emphasize on sensibility and specificity of each MRI approach and we also discuss the current knowledge concerning biological and histopathological substratum that could explain MRI signal with each modality.

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.

MRI measures show significant cerebellar gray matter volume loss in multiple sclerosis and are associated with cerebellar dysfunction

BACKGROUND

Regional atrophy measures may offer useful information about the causes of specific clinical deficits in multiple sclerosis (MS).

OBJECTIVE

To determine the magnitude of cerebellar gray and white matter (GM and WM) atrophy in patients with clinically isolated syndromes (CIS) and MS, and their role in clinical manifestations of cerebellar damage.

METHODS

T1-weighted volumetric magnetic resonance imaging (MRI) of 73 patients [29 CIS, 33 relapsing-remitting MS (RRMS), 11 secondary progressive MS (SPMS)] was compared with 25 controls. GM and WM regions were generated using SPM5 and cerebellar regions delineated. Linear regression was used to investigate differences in tissue-specific cerebellar volumes between groups and the association with clinical measures.

RESULTS

Mean cerebellar GM volume (CGMV) was 100.1 cm(3) in controls, 96.4 cm(3) in CIS patients, 91.8 cm(3) in RRMS patients, and 88.8 cm(3) in SPMS patients. Mean cerebellar WM volumes (CWMV) were 21.3 cm(3), 20.4 cm(3), 19.9 cm(3), and 18.8 cm(3), respectively. CGMV was reduced by 4.8 cm(3) (P = 0.054) in RRMS patients, and 8.5 cm(3) (P = 0.012) in SPMS patients, relative to controls. Only patients with SPMS showed a borderline significant reduction in CWMV compared with controls (mean 2.1 cm(3), P = 0.053). CGMV was significantly smaller in patients assessed as having cerebellar dysfunction compared with patients who had normal cerebellar function. Significant associations of CGMV and CWMV with performance on the nine-hole peg test were also observed.

CONCLUSION

Clinically relevant GM atrophy occurs in the cerebellum of MS patients and is more prominent than WM atrophy. As such, it may provide complementary data to other regional atrophy and intrinsic tissue measures.

Accumulation of cortical lesions in MS: relation with cognitive impairment

BACKGROUND

Gray matter (GM) lesions are frequently found in multiple sclerosis (MS) and their in-vivo detection has been improved using new magnetic resonance imaging sequences, such as double inversion recovery (DIR). However, little is known about progression of GM lesions over time.

OBJECTIVE

To study the longitudinal behavior of GM lesions and to explore their relation to cognitive impairment in MS.

METHODS

DIR images were acquired from 13 MS patients and seven healthy controls at two time points with a median interval of 3 years. At follow-up, all subjects underwent cognitive testing. Lesions were classified as white matter, cortical or hippocampal lesions.

RESULTS

In patients, median cortical lesion number had increased from 18 to 26 at follow-up (P = 0.01), median white matter (WM) lesion number had increased from 56 to 65 (P = 0.02), and no significant increase over time was found for hippocampal lesions. Cortical lesion number at follow-up was significantly higher in secondary progressive (SP) than in relapsing-remitting patients. Significant relations were found between cortical and WM lesion number at follow-up on the one hand and visuospatial memory and processing speed on the other hand. Hippocampal lesion number was related to visuospatial memory.

CONCLUSION

Cortical lesions increase significantly over a 3-year time period, are most frequent in SP patients, and are associated with cognitive impairment.

Gray matter pathology in (chronic) MS: modern views on an early observation

Involvement of the gray matter (GM) in the pathology of multiple sclerosis (MS) was already recognized in the early days of MS research, but the detection of (cortical) GM lesions under the microscope and with magnetic resonance imaging (MRI) techniques was initially suboptimal and could only recently be enhanced. The visualization of GM lesions in vivo opens new doors for studies focusing on clinical, especially cognitive, effects of GM pathology, as well as for monitoring of neuroprotective treatment. However, so far little is known about what causes GM pathology. In this review, several pathogenetic mechanisms will be discussed, affecting the MS brain both from the 'outside-in' and from the 'inside-out'. Also, the use and reliability of MRI atrophy measures as a monitoring tool for GM damage in the therapeutic setting will be reviewed.

Grey matter pathology in clinically early multiple sclerosis: evidence from magnetic resonance imaging

In multiple sclerosis (MS) it is emerging that the most visible element of pathology, white matter (WM) lesions, represents only a fraction of the disease burden borne by the brain; non-lesional WM is also damaged, as is the grey matter (GM). Evidence is also accruing that GM damage may be a major determinant of longer-term outcomes in MS, and that such damage occurs from the earliest clinical stages of the disease. In this review, we focus on the early stages of relapse onset MS, considering the nature, extent and evolution of GM pathology, as determined using magnetic resonance imaging.

3D MPRAGE improves classification of cortical lesions in multiple sclerosis

BACKGROUND

Gray matter lesions are known to be common in multiple sclerosis (MS) and are suspected to play an important role in disease progression and clinical disability. A combination of magnetic resonance imaging (MRI) techniques, double-inversion recovery (DIR), and phase-sensitive inversion recovery (PSIR), has been used for detection and classification of cortical lesions. This study shows that high-resolution three-dimensional (3D) magnetization-prepared rapid acquisition with gradient echo (MPRAGE) improves the classification of cortical lesions by allowing more accurate anatomic localization of lesion morphology.

METHODS

11 patients with MS with previously identified cortical lesions were scanned using DIR, PSIR, and 3D MPRAGE. Lesions were identified on DIR and PSIR and classified as purely intracortical or mixed. MPRAGE images were then examined, and lesions were re-classified based on the new information.

RESULTS

The high signal-to-noise ratio, fine anatomic detail, and clear gray-white matter tissue contrast seen in the MPRAGE images provided superior delineation of lesion borders and surrounding gray-white matter junction, improving classification accuracy. 119 lesions were identified as either intracortical or mixed on DIR/PSIR. In 89 cases, MPRAGE confirmed the classification by DIR/PSIR. In 30 cases, MPRAGE overturned the original classification.

CONCLUSION

Improved classification of cortical lesions was realized by inclusion of high-spatial resolution 3D MPRAGE. This sequence provides unique detail on lesion morphology that is necessary for accurate classification.

Proton magnetic resonance spectroscopy in multiple sclerosis

Proton magnetic resonance spectroscopy ((1)H-MRS) provides tissue metabolic information in vivo. This article reviews the role of MRS-determined metabolic alterations in lesions, normal-appearing white matter, gray matter, and spinal cord in advancing our knowledge of pathologic changes in multiple sclerosis (MS). In addition, the role of MRS in objectively evaluating therapeutic efficacy is reviewed. This potential metabolic information makes MRS a unique tool to follow MS disease evolution, understand its pathogenesis, evaluate the disease severity, establish a prognosis, and objectively evaluate the efficacy of therapeutic interventions.

Segmentation of brain magnetic resonance images for measurement of gray matter atrophy in multiple sclerosis patients

Multiple sclerosis (MS) affects both white matter and gray matter (GM). Measurement of GM volumes is a particularly useful method to estimate the total extent of GM tissue damage because it can be done with conventional magnetic resonance images (MRI). Many algorithms exist for segmentation of GM, but none were specifically designed to handle issues associated with MS, such as atrophy and the effects that MS lesions may have on the classification of GM. A new GM segmentation algorithm has been developed specifically for calculation of GM volumes in MS patients. The new algorithm uses a combination of intensity, anatomical, and morphological probability maps. Several validation tests were performed to evaluate the algorithm in terms of accuracy, reproducibility, and sensitivity to MS lesions. The accuracy tests resulted in error rates of 1.2% and 3.1% for comparisons to BrainWeb and manual tracings, respectively. Similarity indices indicated excellent agreement with the BrainWeb segmentation (0.858-0.975, for various levels of noise and rf inhomogeneity). The scan-rescan reproducibility test resulted in a mean coefficient of variation of 1.1% for GM fraction. Tests of the effects of varying the size of MS lesions revealed a moderate and consistent dependence of GM volumes on T2 lesion volume, which suggests that GM volumes should be corrected for T2 lesion volumes using a simple scale factor in order to eliminate this technical artifact. The new segmentation algorithm can be used for improved measurement of GM volumes in MS patients, and is particularly applicable to retrospective datasets.

Evidence for relative cortical sparing in benign multiple sclerosis: a longitudinal magnetic resonance imaging study

BACKGROUND

Using double inversion recovery (DIR) MRI, cortical lesions can be seen in the brain of patients with multiple sclerosis (MS). The burden of such lesions seems to be well correlated with the severity of MS-related disability.

OBJECTIVE

To investigate whether the extent of cortical damage in patients with benign MS (BMS) might contribute to explain their favorable clinical status.

METHODS

Forty-eight patients with BMS (Expanded Disability Status Scale [EDSS] score < or =3.0 and disease duration > or =15 years) and 96 patients with non-disabling, early relapsing-remitting (RR) MS (EDSS score < or =3.0 and disease duration < or =5 years) were studied. Brain MRI, including a DIR and a fluid-attenuated inversion recovery (FLAIR) sequence, was acquired at baseline and after 12 months. On DIR images, intracortical (ICL) and cortical-subcortical lesions (CSL) were identified and their number and volume calculated. Total white matter (WM) lesion volume was quantified on FLAIR images.

RESULTS

Compared with early RRMS, patients with BMS had lower number of ICL at both study time points (P < or = 0.001 for both comparisons). At one-year follow-up, a significant increase of ICL and CSL number and total volume was observed only in early patients with RRMS. The number and volume of cortical lesions was not correlated with WM lesion volume. Total ICL number at baseline, total cortical lesion volume at baseline, and total cortical lesion volume change were independent predictors of MS phenotype.

CONCLUSION

In patients with BMS, the selective sparing of the cortex from disease-related focal pathology might be one of the factors associated to their favorable clinical status, independently of the (possible) accrual of WM lesions.

Morphology and evolution of cortical lesions in multiple sclerosis. A longitudinal MRI study

Cortical lesions (CLs) can be detected in the majority of patients with established multiple sclerosis (MS), but little is known about their evolution over time. This study was performed to investigate the short-term MRI evolution of CLs, with the ultimate aim to achieve a better in vivo understanding of their nature. Seven hundred and sixty-eight CLs from 107 MS patients (76 with relapsing-remitting [RR] and 31 with secondary progressive [SP] MS) were followed with brain MR examinations, including a double inversion recovery (DIR) sequence, every 6 months for 1 year. CLs' number, volume and morphological features were assessed at each time-point. Six hundred and eighty CLs (88.5%) remained morphologically unchanged during the follow-up period, while 74 (9.6%) showed an increase in size. Only 6 (0.8%) CLs seen at baseline (all in RRMS patients) disappeared at follow-up MRI scans. No enlarging CLs spread into the subcortical white matter. No CLs ever showed gadolinium enhancement. At baseline, the mean number of CLs was higher in SPMS than in RRMS patients (p<0.001), whereas the mean number of new CLs per patient after 1 year did not differ between the two groups. Over a one-year period, CLs can increase their number and size in a relevant proportion of MS patients, without spreading into the subcortical white matter or showing inflammatory features similar to those of white matter lesions. The short-term rate of CLs accumulation does not seem to vary according to the clinical stage of MS.