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X. Wang, M.C.Valdés Hernández, P.A. Armitage, F. Doubal and J.M. Wardlaw University of Edinburgh

Pilot Study to assess white matter lesion progression in longitudinal studies: preliminary findings from The Mild Stroke Study 1. X. Wang, M.C.Valdés Hernández, P.A. Armitage, F. Doubal and J.M. Wardlaw University of Edinburgh. Background and Purpose.

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X. Wang, M.C.Valdés Hernández, P.A. Armitage, F. Doubal and J.M. Wardlaw University of Edinburgh

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  1. Pilot Study to assess white matter lesion progression in longitudinal studies: preliminary findings from The Mild Stroke Study 1 X. Wang, M.C.Valdés Hernández, P.A. Armitage, F. Doubal and J.M. Wardlaw University of Edinburgh

  2. Background and Purpose • White Matter Lesion (WML) segmentation is known to be sensitive to intensity distributions (Valdés Hernández MC et al. European radiology 2010;20(7):1684-91) • A lack of consensus exists in a methodology to assess longitudinal changes in WMLs • We investigate the constraints of assessing WML progression by thresholding on the FLAIR image and by a multispectral approach: MCMxxxVI • We tested the effect of visual intensity normalisation, bias field inhomogeneities correction and automatic intensity normalisation on both methods in 8 representative patients – measuring WML volume at baseline and on average 2.5 years later

  3. Thresholding in FLAIR • Optimum threshold selected in each slice • WML boundary delineation under 3 conditions: • Visual intensity adjustment of the sequence (if needed) • Correction of inhomogeneities in the bias field • Automatic intensity normalisation in each slice Valdés Hernández et. al. European Radiology 2010;20(7):1684-91 Corrected for bias field inhomogeneities: Guillemaud filter Intensity auto. adjusted: 1% of data saturated at low and high intensities Original intensity value

  4. Process of obtaining the WML masks with MCMxxxVI Masks obtained by thresholding in the FLAIR image only. The mask of the stroke lesion is shown in green. The rest of the WMLs are masked in red colour. Original T2*W (left) and FLAIR (middle) images used for the fusion Registered and fused Fused T2*W_FLAIR image after modulating the original sequences in the red-green space (left), Lesion mask before (middle) and after (right) manually removing the false positives in the insular cortex (a typical place for false hyperintense signal).

  5. Numerical results in 8 patients with ischaemic lacunar or minor cortical stroke Abbreviations: BFC: Bias Field Correction IN: Intensity Normalisation

  6. Conclusions • Both FLAIR thresholding and MCMxxxVI methods are highly sensitive to image lesion intensity changes • Similar and more consistent results were obtained by: - MCMxxxVI with and without bias field correction - Thresholding in FLAIR with previous bias field correction and intensity normalisation

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