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Resolution-Dependent Estimates of Multiple Sclerosis Lesion Loads

Published online by Cambridge University Press:  02 December 2014

M.K. Erskine ,
L.L. Cook ,
K.E. Riddle ,
J.R. Mitchell  and
S.J. Karlik
M.K. Erskine
Affiliation:
Department of Physiology, University of Western Ontario, London, Ontario, Canada
L.L. Cook
Affiliation:
Department of Physiology, University of Western Ontario, London, Ontario, Canada
K.E. Riddle
Affiliation:
Department of Diagnostic Radiology and Nuclear Medicine, London Health Sciences Centre, London, Ontario, Canada
J.R. Mitchell
Affiliation:
Calgary Neuroscience Research Group, University of Calgary, Calgary, Alberta, Canada
S.J. Karlik
Affiliation:
Department of Physiology, and Department of Pathology, University of Western Ontario, and Department of Diagnostic Radiology and Nuclear Medicine, London Health Sciences Centre, London, Ontario, Canada
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Abstract:

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Background:

Changes in brain lesion loads assessed with magnetic resonance imaging obtained at 1.5 Telsa (T) are used as a measure of disease evolution in natural history studies and treatment trials of multiple sclerosis.

Methods:

A comparison was made between the total lesion volume and individual lesions observed on 1.5 T images and on high-resolution 4 T images. Lesions were quantified using a computer-assisted segmentation tool.

Results:

There was a 46% increase in the total number of lesions detected with 4 T versus 1.5 T imaging (p<0.005). The 4 T also showed a 60% increase in total lesion volume when compared with the 1.5 T (p<0.005). In several instances, the 1.5 T scans showed individual lesions that coalesced into larger areas of abnormality in the 4 T scans. The relationship between individual lesion volumes was linear (slope 1.231) showing that the lesion volume observed at 4 T increased with the size of the lesion detected at 1.5 T. The 4 T voxels were less than one quarter the size of those used at 1.5 T and there were no consistent differences between their signal-to-noise ratios.

Conclusions:

The increase in signal strength that accompanied the increase in field strength compensated for the loss in signal amplitude produced by the use of smaller voxels. This enabled the acquisition of images with improved resolution, resulting in increased lesion detection at 4 T and larger lesion volumes.

Résumé:

RÉSUMÉ:Introduction:

Les changements du fardeau lésionnel cérébral évalués par imagerie par résonance magnétique obtenue à 1,5 Telsa (T) sont utilisés comme mesure de l’évolution de la maladie dans les études sur l’histoire naturelle de la maladie et au cours des essais thérapeutiques dans la sclérose en plaques.

Méthodes:

Le volume total des lésions et les lésions individuelles observées sur des images 1,5 T ont été comparés aux données obtenues sur des images 4 T à haute résolution. Un outil de segmentation assistée par ordinateur a été utilisé pour quantifier les lésions.

Résultat:

L’imagerie 4 T détectait 46% plus de lésions que l’imagerie 1,5 T (p < 0,005) et un volume total de lésions 60% plus élevé (p < 0,005). Dans plusieurs cas, les scans 1,5 T montraient des lésions individuelles qui se fusionnaient en zones anormales plus vastes sur les scans 4 T. La relation entre le volume individuel des lésions était linéaire (pente de 1,231) démontrant que le volume des lésions observées sur l’imagerie 4 T augmentait selon la taille de la lésion détectée à l’imagerie 1,5 T. Les voxels 4 T étaient moins que le quart de la taille de ceux utilisés à 1,5 T et il n’y avait pas de différence constante entre leur rapport signal-bruit.

Conclusions:

L’augmentation de la forcedu signal qui accompagnait l’augmentation de la force du champ magnétique compensait pour la perte d’amplitude du signal produit par l’utilisation de voxels plus petits, ce qui permettait l’acquisition d’images dont la résolution était meilleure et donc une meilleure détection des lésions et une meilleure appréciation de leur volume par l’imagerie 4 T.

Type
Original Articles
Information
Canadian Journal of Neurological Sciences , Volume 32 , Issue 2 , May 2005 , pp. 205 - 212
Copyright
Copyright © The Canadian Journal of Neurological 2005

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