Image processing steps for acquiring skull-stripped CT template.
(a) Inhomogeneity correction and segmentation of MR, (b) creation of whole brain mask, (c) creation of CSF mask, (d) extraction of whole brain with whole brain mask, (e) spatial normalization of whole brain extract to skull-stripped MNI template, (f) normalization of whole brain mask, (g) normalization of CSF mask, (h, i) creation of probabilistic template for whole brain and CSF, (j) coregistration to inhomogeneity-corrected MR, (k) extraction of skull, (l) spatial normalization of CT coregistered to MR, (m) spatial normalization of skull, (n) creation of probabilistic template for skull, (o) creation of CT template, (p) creation of template mask for scalp-stripping, (q) spatial normalization of original CT with normalization parameter normalizing CT to CT template, (r) inverse normalization of template mask for scalp-stripping to individual mask by using inverse normalization parameter, (s) creation of scalp-stripped CT with individual mask for scalp-stripping, (t) segmentation of scalp-stripped CT into skull, whole brain and CSF by using skull, whole brain and CSF probabilistic templates, (u) creation of skull-stripped CT with whole brain segment, (v) skull stripped CT coregistered to MR, (w) spatial normalization of skull-stripped CT, (x) creation of skull-stripped CT template by averaging. CSF = cerebrospinal fluid, MNI = Montreal Neurological Institute