Pathological correlates of 7T MRI: how far can we image MS pathology in the living patient
ECTRIMS Online Library. Hametner S. 09/13/19; 279559; 299
Simon Hametner
Simon Hametner
Contributions
Abstract

Abstract: 299

Type: Educational Session

Abstract Category: Educational Session 24: Pathology of MS

S. Hametner

Institute of Neurology, Medical University of Vienna, Vienna, Austria

Magnetic resonance imaging (MRI) delivers indispensable information already at 1.5 and 3 Tesla (T) in the context of Multiple Sclerosis (MS). Lesion numbers, total lesion volume, lesion localization, blood-brain barrier damage, edema, hypoxia, axonal loss, myelin loss and remyelination can be detected and in part also quantified using 1.5 and 3T scanners. With the availability of 7T systems, additional features of MS pathology can be imaged in-vivo. Particular advantages of ultra-high field systems are higher resolution, shorter scan times and larger susceptibility effects, which can be exploited for specialized, e.g. iron-sensitive, MRI contrasts. The mentioned advantages allow better depiction of MS pathology in individual patients and smaller study cohort sizes to detect significant progression of MS pathology at the group level.
Advanced MRI techniques applied in MS imaging studies include different iron-sensitive methods, such as susceptibility-weighted imaging (SWI), T2* / R2* imaging and quantitative susceptibility mapping (QSM). However, these methods are not specific for iron but influenced by other brain constituents such as myelin and fiber orientation. Presence of diamagnetic myelin leads to a signal decrease in QSM, while it increases R2*. This differential effect of myelin has recently been demonstrated using MRI-histopathological correlations. Therefore, iron-sensitive imaging is challenging in myelin-rich white matter. Furthermore, signal alterations in MS lesions need to be interpreted considering lesional myelin loss. Cortical MS lesions are difficult to visualize by standard MRI, however, their concomitant myelin and iron loss delivers superior depiction of cortical lesions in e.g. 7T R2* images.
Iron-sensitive MRI can be used for imaging of the central vein sign (CVS) in MS lesions, which helps differentiating MS lesions from lesions of other etiology. Iron-sensitive imaging furthermore reveals iron rims around a subset of MS lesions. Histopathological correlations revealed ongoing and chronic rim inflammation and demyelination, which corresponded to lesion expansion in-vivo. However, the clinical meaning of iron rims still needs to be determined. The early evolution of iron-rim lesions has been studied using the contrast agent Gadolinium, which revealed that only a fraction of centripetally enhancing lesions but no centrifugally enhancing lesions developed into iron-rim lesions.
Disclosure: Simon Hametner: nothing to disclose

Abstract: 299

Type: Educational Session

Abstract Category: Educational Session 24: Pathology of MS

S. Hametner

Institute of Neurology, Medical University of Vienna, Vienna, Austria

Magnetic resonance imaging (MRI) delivers indispensable information already at 1.5 and 3 Tesla (T) in the context of Multiple Sclerosis (MS). Lesion numbers, total lesion volume, lesion localization, blood-brain barrier damage, edema, hypoxia, axonal loss, myelin loss and remyelination can be detected and in part also quantified using 1.5 and 3T scanners. With the availability of 7T systems, additional features of MS pathology can be imaged in-vivo. Particular advantages of ultra-high field systems are higher resolution, shorter scan times and larger susceptibility effects, which can be exploited for specialized, e.g. iron-sensitive, MRI contrasts. The mentioned advantages allow better depiction of MS pathology in individual patients and smaller study cohort sizes to detect significant progression of MS pathology at the group level.
Advanced MRI techniques applied in MS imaging studies include different iron-sensitive methods, such as susceptibility-weighted imaging (SWI), T2* / R2* imaging and quantitative susceptibility mapping (QSM). However, these methods are not specific for iron but influenced by other brain constituents such as myelin and fiber orientation. Presence of diamagnetic myelin leads to a signal decrease in QSM, while it increases R2*. This differential effect of myelin has recently been demonstrated using MRI-histopathological correlations. Therefore, iron-sensitive imaging is challenging in myelin-rich white matter. Furthermore, signal alterations in MS lesions need to be interpreted considering lesional myelin loss. Cortical MS lesions are difficult to visualize by standard MRI, however, their concomitant myelin and iron loss delivers superior depiction of cortical lesions in e.g. 7T R2* images.
Iron-sensitive MRI can be used for imaging of the central vein sign (CVS) in MS lesions, which helps differentiating MS lesions from lesions of other etiology. Iron-sensitive imaging furthermore reveals iron rims around a subset of MS lesions. Histopathological correlations revealed ongoing and chronic rim inflammation and demyelination, which corresponded to lesion expansion in-vivo. However, the clinical meaning of iron rims still needs to be determined. The early evolution of iron-rim lesions has been studied using the contrast agent Gadolinium, which revealed that only a fraction of centripetally enhancing lesions but no centrifugally enhancing lesions developed into iron-rim lesions.
Disclosure: Simon Hametner: nothing to disclose

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