In fetal brain MRI, most of the high-resolution reconstruction algorithms rely on brain segmentation as a preprocessing step. Manual brain segmentation is however highly time-consuming and therefore not a realistic solution. In this work, we assess on a large dataset the performance of Multiple Atlas Fusion (MAF) strategies to automatically address this problem. Firstly, we show that MAF significantly increase the accuracy of brain segmentation as regards single-atlas strategy. Secondly, we show that MAF compares favorably with the most recent approach (Dice above 0.90). Finally, we show that MAF could in turn provide an enhancement in terms of reconstruction quality.
DESCRIPTION OF THE PURPOSEMost of the high-resolution reconstruction algorithms used in fetal MRI 1-10 rely only on brain tissue-relevant voxels of low-resolution (LR) images. In general, those algorithms need to perform brain segmentation as a preprocessing step. This brain extraction is essential to ensure good results of the subsequent image processing steps (denoising, bias correction, motion estimation, and super-resolution reconstruction). Despite of manual brain segmentation can be performed, it is highly time-consuming (around 15 minutes per stack of 15 slices) and not a realistic solution for large-scale studies. In the literature, accurate brain extraction tools have been developed for adult and infant brain MRI. 11, 12 But, fetal brain MRI differs a lot from neonatal or adult imaging in terms of image content (with maternal tissues surrounding the fetal brain), image contrast and brain size. Consequently, those tools are not well adapted to fetal MRI.Few works have addressed the automatic extraction of fetal brain in MRI. Two major types of approaches can be distinguished, either template-based segmentation 13-15 or machine learning 16-18 techniques. The first attempt 13 of fetal brain extraction proposed first to estimate the location of the eyes (based on rigid template registration) in order to segment the fetal brain using contrast, morphological and biometrical prior information. This method gave precise results in 22 out of 24 stacks of fetuses aged between 30 and 53 gestational weeks (GW). However, they relied on the assumption of low motion between slices that limits the robustness of the method to clinical databases where large motion can occur. More recently, Taleb et al. 14 presented an efficient brain extraction method based on single age-specific template segmentation (affine template registration) and fusion of orthogonal segmentations (transversal, coronal and sagittal) where final brain masks were successfully estimated in 82% of the cases. The validation was however rather qualitative (i.e. only success or failure label was given to the results). A supervised approach, 16 based on a two-phase random forest classifier, was adopted in order to obtain a method applicable to all fetal ages and more robust with respect to motion between slices. This method has shown comparable results to the method 13 but the whole brain was c...