Image Processing Reference
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neonate brain atlas [ 10 ]. Brain masks for the early 30 week EGA scan were
propagated from the 40 week EGA mask. All masks were checked and manually
corrected to exclude any non-brain tissue that can generate mislabelled voxels.
We segmented each infant brain into six different parts: grey matter, white
matter, cerebrospinal fluid (CSF), deep gray matter, cerebellum and brainstem,
using a preterm specific Expectation-Maximization (EM) segmentation with
prior relaxation [ 11 ].
Fig. 1. Brain segmentation into grey matter (GM), white matter (WM), cerebrospinal
fluid (CSF), deep grey matter, cerebellum and brainstem of the same infant for the
two different time points: 30 and 40 weeks EGA respectively
In order to separate the prefrontal cortex from the rest of the brain, we used
a multi-contrast human neonatal brain atlas [ 12 ] registered to the space of the
early and late scans using non-rigid registration. The corresponding regions of
the prefrontal cortex were grouped by hemisphere: left and right PFC.
The white matter segmentation was then combined with the delineation of
the PFC. Any segmentation errors were corrected by morphological operations
(largest component and filling of the holes) to ensure a topologically correct
surface. The processed left and right white matter PFC segmentation were used
to create smooth triangle-based meshes of each surface.
Joint-Spectral Matching of the Cortical Surface. A rigid Coherent Point
Drift (CPD) algorithm (translation and rotation) was used to find an initial
correspondence for the intra-subject prefrontal cortex at the two different time-
points [ 13 ]. Since the two paired meshes are very different in shape, size and mor-
phology, the CPD is preferable to the Feature Oriented Correspondence using
Spectral Regularization (FOCUSR) [ 14 ], a conventional spectral method that
requires a robust eigenvector reordering, which is challenging with our meshes.
After initial correspondence was established, Joint-Spectral Matching (JSM) was
used to find the correspondence for the intra-subject prefrontal cortex at 30 week
EGA and term equivalent age for each subject [ 9 ]. The use of a joint-spectral
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