Magnetization Transfer Imaging in Multiple Sclerosis

Magnetization transfer (MT) is a relatively new way of generating contrast in magnetic resonance (MR) images that is sensitive to the density of the macromolecules found throughout tissue structures such as membranes, myelin, and organelles. MT imaging (MTI) can provide a quantitative measure of macromolecular density, and therefore of tissue damage, and has been applied in the central nervous system in multiple sclerosis (MS) and other diseases. This article introduces the contrast mechanisms behind MTI and gives some practical guidance about implementing MTI and about quantitative analysis of the MT scans. An overview of MT measurements made in animal studies, in postmortem tissue samples, and in other demyelinating diseases attempts to rationalize the pathological basis of changes in MT contrast in MS. The application of MTI to MS is reviewed, with emphasis on the contribution that MTI has made to the current understanding of the MS disease process, both its natural history and the response to treatment. The pathological basis of abnormal MT contrast is still open to debate, with many conflicting reports; indeed, it is unlikely that a simple measure of MT effect will reveal the details of pathology that is a combination of inflammation, demyelination, remyelination, and axonal loss. There is no doubt, however, that MT measurements have contributed to the current understanding of both disease progression and the response to treatment and will prove to be a valuable tool in the future, particularly if more refined techniques can be applied practically in multicenter studies.     

Magnetic Resonance Imaging of Multiple Sclerosis

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

A Magnetization Transfer MRI Study of Deep Gray Matter Involvement in Multiple Sclerosis

BACKGROUND/PURPOSE: Gray matter involvement in multiple sclerosis (MS) is of growing interest with respect to disease pathogenesis. Magnetization transfer imaging (MTI), an advanced MRI technique, is sensitive to disease in normal appearing white matter (NAWM) in patients with MS. DESIGN/METHODS: We tested if MTI detected subcortical (deep) gray matter abnormalities in patients with MS (n= 60) vs. age-matched normal controls (NL, n= 20). Magnetization transfer ratio (MTR) maps were produced from axial proton density, conventional spin-echo, 5 mm gapless slices covering the whole brain. Region-of-interest-derived MTR histograms for the caudate, putamen, globus pallidus, thalamus, and NAWM were obtained. Whole brain MTR was also measured. RESULTS: Mean whole brain MTR and the peak position of the NAWM MTR histogram were lower in patients with MS than NL (P < .001) and mean whole brain MTR was lower in secondary progressive (SP, n= 10) than relapsing-remitting (RR, n= 50, P < .001) patients. However, none of the subcortical gray matter nuclei showed MTR differences in MS vs. NL, RR vs. SP, or SP vs. NL. CONCLUSIONS: The MTI technique used in this cohort was relatively insensitive to disease in the deep gray matter nuclei despite showing sensitivity for whole brain disease in MS. It remains to be determined if other MRI techniques are more sensitive than MTI for detecting pathology in these areas.     

Seven‐Tesla Magnetization Transfer Imaging to Detect Multiple Sclerosis White Matter Lesions

BACKGROUND AND PURPOSE

Fluid‐attenuated inversion recovery (FLAIR) imaging at 3 Tesla (T) field strength is the most sensitive modality for detecting white matter lesions in multiple sclerosis. While 7T FLAIR is effective in detecting cortical lesions, it has not been fully optimized for visualization of white matter lesions and thus has not been used for delineating lesions in quantitative magnetic resonance imaging (MRI) studies of the normal appearing white matter in multiple sclerosis. Therefore, we aimed to evaluate the sensitivity of 7T magnetization‐transfer‐weighted (MT_w) images in the detection of white matter lesions compared with 3T‐FLAIR.

METHODS

Fifteen patients with clinically isolated syndrome, 6 with multiple sclerosis, and 10 healthy participants were scanned with 7T 3‐dimensional (D) MT_w and 3T‐2D‐FLAIR sequences on the same day. White matter lesions visible on either sequence were delineated.

RESULTS

Of 662 lesions identified on 3T‐2D‐FLAIR images, 652 were detected on 7T‐3D‐MT_w images (sensitivity, 98%; 95% confidence interval, 97% to 99%). The Spearman correlation coefficient between lesion loads estimated by the two sequences was .910. The intrarater and interrater reliability for 7T‐3D‐MT_w images was good with an intraclass correlation coefficient (ICC) of 98.4% and 81.8%, which is similar to that for 3T‐2D‐FLAIR images (ICC 96.1% and 96.7%).

CONCLUSION

Seven‐Tesla MT_w sequences detected most of the white matter lesions identified by FLAIR at 3T. This suggests that 7T‐MT_w imaging is a robust alternative for detecting demyelinating lesions in addition to 3T‐FLAIR. Future studies need to compare the roles of optimized 7T‐FLAIR and of 7T‐MT_w imaging.     

Magnetic Resonance Imaging Of The Central Nervous System

Magnetic resonance (MR) is a powerful new imaging modality which has recently become competitive with X-ray computed tomography (CT) for imaging of the central nervous system (CNS). The advantages of MR include lack of ionizing radiation and the necessity to use iodinated contrast. MR is able to image directly in the transaxial, coronal, and sagittal planes. With appropriate pulsing sequences, MR is more sensitive than CT in the detection of early disease associated with increased water content. Included in this category are multiple sclerosis, early infarcts, small tumours, and inflammatory lesions. MR is superior to CT in the posterior fossa due to beam hardening artifacts in the latter modality. In the cord, MR is useful in the evaluation of syringomyelia, spinal dysraphism, and intramedullary tumours.

Due to its increased sensitivity in the detection of early disease, MR should generally be used as the initial screening procedure in the evaluationof possible intracranial disease. Current limita-tionsof MR include longer single slice imaging times, thicker slices, inability to use contrast agents to define blood/brain barrier breakdown, and the inabilityto image calcification and cortical bone. Patients on cardiac monitors or on respirators and those with intracranial aneurysm clips and cardiac pacemakers are currently excluded from MR imaging.     

多发性硬化脑内磁共振病灶分布及其特征(附203例2年MRI随访结果)

目的　为了解多发性硬化 ( multiple sclerosis,MS)的病灶特点 ,对确诊的 2 0 3例 MS患者进行系列磁共振 ( magnetic resonance,image,MRI)观察。方法　选择确诊的缓解 -复发型 MS患者 2 0 3例 ,每 6个月检查头颅MRI一次。结果　 ( 1 ) 2 0 3例 MS患者中 ,1 72 ( 84 .7% )例脑 MRI显示脱髓鞘病灶。其中有胼胝体病灶者 90例( 5 2 % ) ,有脑干病灶者 1 0 6例 ( 6 2 % ) ,有小脑病灶者 4 6例 ( 2 8% ) ,有与脑室连接的病灶者 1 5 7例 ( 91 % ) ,有典型的卵圆形病灶者 98例 ( 5 7% ) ,病灶长轴与侧脑室切线垂直的病灶占总病灶一半以上者 1 30例 ( 76 % )。( 2 ) 2 0 3例MS患者中 ,大脑半球内和脑内无病灶者分别为 4 1例 ( 2 0 % )和 31例 ( 1 5 % )。仅脑干有病灶者 6例 ( 3% ) ,仅小脑有病灶者 2例 ( 1 % ) ,脑干和小脑都有病灶者 2例 ( 1 % )。 ( 3) 2 0 3例共检查 82 7例次 MRI,有活动病灶者 77例( 4 1 % ) ,共有活动病灶 2 6 1个 ,分布在大脑、小脑和脑干者依次为 2 2 3、1 0和 2 8个。结论　 ( 1 )在确诊 MS患者中 ,多数 ( 85 % )脑 MRI有脱髓鞘病灶 ,与欧美资料相近。( 2 )脑内有病灶者中 ,小脑有病灶者占 2 8% ,较欧美报道为低。 ( 3) T2像发现活动病灶的机率不高 ,多次复查能提高病灶的检出率 ( 4 1     

Magnetization transfer imaging of multiple sclerosis

While conventional magnetic resonance imaging (MRI) measures signal primarily from the hydrogen nuclei of water, magnetization transfer (MT) MRI indirectly detects macromolecular associated hydrogen nuclei via their magnetic interaction with the observable water. In the normal adult CNS, white matter exhibits the largest MT effect due to the macromolecular content of the highly structured and lipid rich myelin. Pathologies which alter the structural integrity and the relative macromolecular-water composition, such as multiple sclerosis (MS), therefore show abnormal MT. Conventional MRI, which has a high MS lesion detection sensitivity but poor specificity in terms of differentiating the pathological state of a plaque, can thus be supplemented by MT to provide more specific information on the extent of demyelination and axonal loss. In this paper we review the basic concepts of MT imaging and its role in MS lesion characterization.Financial support was provided by the Medical Research Council of Canada, Fonds de la Recherche en Santé du Québec, and the Killam Foundation.     

Functional Magnetic Resonance Imaging of Working Memory among Multiple Sclerosis Patients

BACKGROUND AND PURPOSE: Verbal working memory (VWM) deficits have been a well-replicated finding among patients with multiple sclerosis (MS). Functional magnetic resonance imaging (FMRI) studies have described a VWM system in healthy samples; however, functional neuroimaging of this system among MS patients is just beginning to appear. METHODS: Fifteen MS patients and 15 sex-, age-, education-, and IQ-matched healthy control (HC) participants completed a 2-Back VWM task as whole-brain FMRI was conducted. RESULTS: Each group exhibited increased brain activity compared to the O-Back control task in regions associated with the 2-Back in previous neuroimaging studies. These included Broca's area, supplementary motor area (SMA), premotor cortices (PMC), and dorsolateral prefrontal cortices (DLPFC). MS patients exhibited greater cortical activity than did HC participants in left primary motor and somatosensory cortices, PMC, DLPFC, anterior cingulate, and bilateral SMA. MS patients exhibited relatively less activation in Broca's area, bilateral cerebellum, and other regions not typically associated with the 2-Back (e.g., right fusiform gyrus, left lingual gyrus, right hippocampus). Performance accuracy and reaction time did not differ between groups. CONCLUSIONS: Normal performance of a challenging VWM task among high-functioning MS patients is associated with a shift toward greater activity in regions related to sensorimotor functions and anterior attentional/executive components of the VWM system. Posterior memory storage systems appeared unaffected, while portions of the visual processing and subvocal rehearsal systems were less active. Although a shift in neural activity was noted relative to HC participants, deviation from regions normally involved in VWM function was not observed in this patient sample.     

磁共振弥散张量成像在脑血管病中的应用

磁共振弥散张量成像（DTI）是一种较新的成像技术,主要用于评估影响脑白质尤其是白质纤维束完整性的疾病,是当前惟一的一种能有效观察和追踪脑白质纤维束的非侵入性检查方法。该技术可定量分析病变组织和正常组织的弥散特征,直观显示颅内病变与白质纤维之间的关系,为诊断疾病和判断预后提供更多的信息。本文就DTI基本原理及其在脑血管病中的临床应用作一概述。     

Magnetic Resonance Imaging of Neurodegenerative Diseases

Magnetic resonance imaging (MRI) has become an important diagnostic tool in the evaluation of neurodegenerative diseases. Although MRI currently does not yield sufficient predictive power to provide a diagnosis in most individual cases, important features have been identified in population studies that help support or exclude a clinical diagnosis under consideration. In parkinsonian patients, putamenal signal hypointensity is commonly observed in patients with atypical parkinsonism. In demented patients, hippocampal atrophy and prolonged T2 relaxation may help identify individuals with Alzheimer's disease. Caudate and putamenal atrophy are seen in Huntington's disease and may serve as markers of disease progression.     

颞叶癫患者的头颅磁共振显像异常表现分析

目的对颞叶癫(TLE)患者头颅磁共振成像(MRI)异常表现进行分析,为临床诊治TLE提供参考。方法对56例TLE患者的头颅MRI异常表现进行分析总结。结果 56例TLE患者头颅MRI主要表现为海马硬化、颞叶软化灶、颞叶肿瘤、颞叶皮质萎缩等。其中,颞叶肿瘤类型多样,主要为少突胶质瘤、星形细胞瘤、脑膜瘤。结论 TLE患者头颅MRI异常表现复杂多样,正确掌握其特点有助于TLE的诊治。     

Multimodal Magnetic Resonance Imaging for Brain Disorders: Advances and Perspectives

Modern brain imaging technologies play essential roles in our understanding of brain information processing and the mechanisms of brain disorders. Magnetic Resonance Imaging (MRI) and Diffusion Tensor Imaging (DTI) can image the anatomy and structure of the brain. In addition, functional MRI (fMRI) can identify active regions, patterns of functional connectivities and functional networks during either tasks that are specifically related to various aspects of brain function or during the resting state. The merging of such structural and functional information obtained from brain imaging may be able to enhance our understanding of how the brain works and how its diseases can occur. In this paper, we will review advances in both methodologies and clinical applications of multimodal MRI technologies, including MRI, DTI, and fMRI. We will also give our perspectives for the future in these fields. The ultimate goal of our study is to find early biomarkers based on multimodal neuroimages and genome datasets for brain disorders. More importantly, future studies should focus on detecting exactly where and how these brain disorders affect the human brain. It would also be also very interesting to identify the genetic basis of the anatomical and functional abnormalities in the brains of people who have neurological and psychiatric disorders. We believe that we can use brain images to obtain effective biomarkers for various brain disorders with the aid of developing computational methods and models.