Falx Cerebri Segmentation via Multi-atlas Boundary Fusion

Abstract

The falx cerebri is a meningeal projection of dura in the brain, separating the cerebral hemispheres. It has stiffer mechanical properties than surrounding tissue and must be accurately segmented for building computational models of traumatic brain injury. In this work, we propose a method to segment the falx using T1-weighted magnetic resonance images (MRI) and susceptibility-weighted MRI (SWI). Multi-atlas whole brain segmentation is performed using the T1-weighted MRI and the gray matter cerebrum labels are extended into the longitudinal fissure using fast marching to find an initial estimate of the falx. To correct the falx boundaries, we register and then deform a set of SWI with manually delineated falx boundaries into the subject space. The continuous-STAPLE algorithm fuses sets of corresponding points to produce an estimate of the corrected falx boundary. Correspondence between points on the deformed falx boundaries is obtained using coherent point drift. We compare our method to manual ground truth, a multi-atlas approach without correction, and single-atlas approaches.

Keywords: Falx cerebri; MRI; boundary fusion; segmentation.

Fig. 1

Shown is a (a) 3D rendering of the falx (red) with the cerebrum overlaid as a gray transparency, the manual delineation of the falx (red contour) in (b) MPRAGE-PG, and (c) SWI. The inferior sagittal sinus (red arrow), straight sinus (green arrow) and superior sagittal sinus (blue arrow) are highlighted.

Fig. 2

Coronal view of the steps in the initial falx segmentation method: (a) the multi-atlas segmentation; (b) the fast march extended segmentation labels; (c) the label map showing voxels belonging to left hemisphere GM labels (pale yellow) and right hemisphere GM labels (blue); and (d) the initial falx segmentation (yellow). The inner and outer cortical surfaces are overlaid as green and cyan contours respectively.

Fig. 3

(a) Yellow, green, magenta, and cyan points show the boundary coordinates after deformable registration from the four atlases, overlaid on the MPRAGE-PG. (b) Fused boundary (red contour) using traditional STAPLE. (c) Fused boundary coordinates (red dots) using continuous-STAPLE. The white rectangle shows an area of interest.

Fig. 4

3D rendering of the falx showing (a) the manual delineation, the results of single atlas registration for the (b) worst and (c) best cases; (d) the initial falx estimate and (e) after refinement. The color of the surface indicates the distance in mm to the manual delineation on a log-scale.