A Skeleton and Deformation Based Model for Neonatal Pial Surface Reconstruction in Preterm Newborns

Abstract

Though quantification of cortical thickness characterizes a main aspect of morphology in developing brains, it is challenged in the analysis of neonatal brain MRI due to inaccurate pial surface extraction. In this study, we propose a pial surface reconstruction method to address for the relatively large partial volume (PV) within the sulcal basin. The new approach leverages the benefits of using new skeletonization and the deformation models with a new gradient feature. The proposed skeletonization method combines the voxels representing the skeleton of cerebrospinal fluid partial volume (CSF-PV) with the voxels of the medial plane of the gray matter (GM) volume of the sulcus where no CSF-PV is estimated due to the squashed sulcal bank and the limited resolution. Subsequently, the outer cortical boundary is identified by first deforming the initial surface to the skeleton, then refining it using the gradient model characterizing the subtle edges representing the “ground truth” of the GM/CSF boundary. Our landmark-based evaluation showed that the initial boundary identified by the skeletonization was already close to the “ground truth” of the GM/CSF boundary (0.4 mm distant). Furthermore, this was significantly improved by the reconstruction of the final pial surface $( \lt 0.1$ mm; $\mathrm {p}\lt 0.0001)$. The mean cortical thickness measured through our pipeline positively correlated with postmenstrual age (PMA) at scan $( \mathrm {p}\lt 0.0001)$. The range of the measurement was biologically reasonable (1.4 mm at 28 weeks of PMA to 2.2 mm at term equivalent $vs$. young adults: 2.5–3.5 mm) and was quite close to past reports (2.1 mm at term).