EURON and THEME joint PhD meeting

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38 EURON and THEME joint meeting 2011 Tract specific morphological and parametric reproducibility RMH Besseling 1,2,3 , JFA Jansen 1,2 , GM Overvliet 1,2,3 , MJ Vaessen 1,2,3 , PAM Hofman 1,2,3 , AP Aldenkamp 1,2,3 , WH Backes 1,2 1 Department of Radiology; 2 School for Mental Health and Neuroscience, Maastricht University Medical Center (MUMC+), Maastricht, the Netherlands; 3 Epilepsy Center Kempenhaeghe, Heeze, the Netherlands. Rationale Tractography based tract segmentations were used to study reproducibility characteristics of tract volume as well as diffusion tensor metrics at the tract level. In addition, the relatively new diffusion contrast tract density imaging (TDI) was studied at the tract specific level. Furthermore, the reproducibility of the shape of the tracts (tract morphology) was assessed, which included the reproducibility of complete tract segmentations (extended) compared to tract segmentation excluding the directly subcortical projections (proximal). Methods Diffusion weighted imaging (DWI) was performed twice in 9 healthy subjects (28±6 y) on an 3T Philips Achieva scanner using: 128 gradient directions, voxel size of 2x2x2 mm 3 , and b=1200 s/mm 2 . Standard space seed and inclusion ROIs were mapped non-linearly to native DWI space, and subsequently constrained spherical deconvolution (CSD) probabilistic tractography was performed. The selected tracts were the genu of the corpus callosum, the cingulum, the pyramidal tract, the optic radiation, and the arcuate fasciculus. Tractograms were converted to tract density maps and thresholded to create tract segmentations that were used as ROIs to investigate tract fractional anisotropy (FA), apparent diffusion coefficient (ADC), volume and TDI. In addition, tract segmentations were mapped back to standard space to calculate between-session morphological overlap using the Dice similarity coefficient (DSC). Reproducibility of FA, ADC, volume and TDI was quantified using the coefficient of variation (COV) and the interclass correlation coefficient (ICC). Results For all metrics, reproducibility differed strongly between tracts and between proximal and extended tract segmentations. For FA, the proximal reproducibility values were: COV=1.6-2.7%, ICC=0.65-0.94. For ADC, comparable values were found (COV=1.5-3.5%, ICC=0.66-0.92). For volume, proximal COV=6.1-22%, proximal ICC=0.64-0.96 (0.029 for the arcuate fasciculus). For TDI, proximal
39 EURON and THEME joint meeting 2011 COV=7.7-27% and not in all tracts accurate ICC values could be estimated. Morphological overlap as expressed by DSC ranged from 0.70 (arcuate fasciculus, extended) to 0.92 (corpus callosum, proximal). For a data subset of 66 gradient directions, DSC values were reduced for each tract with approximately 5%. Conclusion Estimates of tract FA and ADC are reliable, based on favorable COV and ICC values. Tract volume has worse COV values but maintains high ICC values. Tract TDI is the least reliable contrast, due to high COV combined with low ICC. Furthermore, our approach results in very high between-session morphological correspondence (up to DSC=0.92). Reliability is reduced in extended tract segmentations compared to the proximal segmentations. Since both types of segmentations differ primarily in their extent of subcortical projections, a reduced sensitivity in detection of subcortical changes in tract morphology can be expected.
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List of Participants 103 EURON and
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Nuersailike Abuduwali University of
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Marianne Eisenhardt University of B
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Sabine Klein University of Bonn PhD
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Viktoriya Peeva University of Bonn
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Sylvie van der Kruijs Maastricht Un
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EURON and THEME joint PhD meeting

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