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Investigating the spinal cord atrophy measurement on MRI from two aspects : physiological variations and longitudinal measurement methods Wang, Chunfang

Abstract

Spinal cord atrophy is a valuable biomarker in multiple sclerosis (MS) for its significant correlation with physical disability. Measurement of spinal cord atrophy on MRI may be possibly confounded by fluctuations in water content, and the high measurement variance in previous longitudinal studies can be possibly reduced by registration-based methods. In this thesis, we investigated the effect of change in water content due to hydration status on cord cross-sectional area (CSA) measurement, and the applicability of three registration-based methods for longitudinal cord atrophy measurement. Our first hypothesis is that dehydration can decrease the cord CSA measurement on MRI. We found a mean decrease of 0.65% in CSA on scans collected from ten controls following a dehydration protocol using two independent cross-sectional CSA measurement methods. Our result demonstrates that change in water content of the cord is associated with measurable change in cord CSA. The second main hypothesis is that registration-based methods can decrease the variance in longitudinal cord atrophy measurement by using the signal from multiple scans to improve robustness to image noise and artifacts and by regularization of the registration to constrain the degrees of freedom. We implemented three algorithms: boundary shift integral based on rigid registration, Jacobian integration based on deformable registration and scale factor computation based on constrained registration (composed of rigid and scale transformation). We evaluated the three registration-based methods by comparing them to two cross-sectional methods, as applied to three longitudinal data sets: 1) images with simulated cord atrophy; 2) images acquired in the dehydration study described above; and 3) images of 15 MS patients over a two-year interval. Our main result was that while registration-based methods achieved more accurate results on simulation data sets and overall smaller measurement variance, they were not as sensitive, reporting no dehydration effect and smaller magnitude of patient cord atrophy. We argue that the limited spatial resolution of 1mm of MR scans in our experiment is possibly the main reason and future studies of cord atrophy measurement using registration-based methods should be conducted on MR scans with a high spatial resolution such as 0.5mm.

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Attribution-NonCommercial-NoDerivs 2.5 Canada

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