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Fast automatic segmentation of thalamic nuclei from MP2RAGE acquisition at 7 Tesla

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Document pages: 13 pages

Abstract: Purpose: Thalamic nuclei are largely invisible in conventional MRI due topoor contrast. Thalamus Optimized Multi-Atlas Segmentation (THOMAS) providesautomatic segmentation of 12 thalamic nuclei using white-matter-nulled (WMn)MPRAGE sequence at 7T. Application of THOMAS to Magnetization Prepared 2 RapidGradient Echo (MP2RAGE) sequence acquired at 7T has been investigated in thisstudy.Methods: 8 healthy volunteers and 5 pediatric-onset multiple sclerosispatients were recruited at the Children s Hospital of Philadelphia and scannedat Siemens 7T with WMn-MPRAGE and multi-echo MP2RAGE (ME-MP2RAGE) sequences.White-matter-nulled contrast was synthesized (MP2-SYN) from T1 maps fromME-MP2RAGE sequence. Thalamic nuclei were segmented using THOMAS joint labelfusion algorithm from WMn-MPRAGE and MP2-SYN datasets. THOMAS pipeline wasmodified to use majority voting to segment the bias corrected MP2-UNI images.Thalamic nuclei from MP2-SYN and MP2-UNI images were evaluated againstcorresponding nuclei obtained from WMn-MPRAGE images using dice coefficients,volume similarity indices (VSI) and distance between centroids.Results: For MP2-SYN, dice > 0.85 and VSI > 0.95 was achieved for the 5larger nuclei and dice > 0.6 and VSI > 0.7 was achieved for the 7 smallernuclei. The dice and VSI were slightly higher whilst the distance betweencentroids were smaller for MP2-SYN compared to MP2-UNI, indicating improvedperformance using the synthesized WMn image.Discussion: THOMAS algorithm can successfully segment thalamic nuclei inroutinely acquired bias-free MP2RAGE images with essentially equivalent qualitywhen evaluated against WMn-MPRAGE, hence has wider applicability in studiesfocused on thalamic involvement in aging and disease.

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