Segmentation of cranial bone after craniectomy

Tato práce se zabývá segmentací klenby lebeční v CT snímcích pacientů po kraniektomii. Zadaná problematika byla řešena pomocí segmentační architektury U-Net, konkrétně její 2D i 3D variantou. S první verzí architektury bylo dosaženo průměrné hodnoty Jaccardova indexu 89,4 %, u druhé úspěšnosti 67,1 % vyhodnocené stejnou metrikou. Při zaměření na oblasti po chirurgickém zákroku nebyl u výsledků jednotlivých variant již tak velký rozdíl, zjištěný Jaccardův index pro 2D síťě byl průměrně 98,4 % a pro 3D verze 97,0 %.This thesis deals with the segmentation of cranial bone in CT patient’s data after craniectomy. The U-Net architecture in 2D and 3D variant were selected for the intention of solving this problem. Jaccard index for 2D U-Net was evaluate as 89,4 % and for 3D U-Net it was 67,1 %. In the area after surgical intervention evaluating index has smaller difference between both variant, the average success rate of skull classification was 98,4 % for 2D U-Net and 97,0 % for 3D U-Net.

Soft-max boosting

International audienceThe standard multi-class classification risk, based on the binary loss, is rarely directly minimized. This is due to (i) the lack of convexity and (ii) the lack of smoothness (and even continuity). The classic approach consists in minimizing instead a convex surrogate. In this paper, we propose to replace the usually considered deterministic decision rule by a stochastic one, which allows obtaining a smooth risk (generalizing the expected binary loss, and more generally the cost-sensitive loss). Practically, this (empirical) risk is minimized by performing a gradient descent in the function space linearly spanned by a base learner (a.k.a. boosting). We provide a convergence analysis of the resulting algorithm and experiment it on a bunch of synthetic and real-world data sets (with noiseless and noisy domains, compared to convex and non-convex boosters)