		       Colin 27 Average Brain
		    Stereotaxic Registration Model


This is a stereotaxic average of 27 T1-weighted MRI scans of the same
individual.  This average dataset was created in a two step process.
First, each of the 27 T1-weighted scans were registered to stereotaxic
space using the mritotal procedure and resampled onto a 1mm grid in
stereotaxicc space.  All 27 scans were averaged together to create an
initial average.  This average volume was used as a target for the
second phase of registration where each original T1-weighted MRI was
re-registered in stereotaxic space.  This procedure has the advantage
of removing the small variance in intra-subject mapping in stereotaxic
space associated with the use of a multi-subject average.  This
procedure has been described in detail in:

   Holmes CJ, Hoge R, Collins L, Woods R, Toga AW, Evans AC.
   "Enhancement of MR images using registration for signal averaging."
   J Comput Assist Tomogr. 1998 Mar-Apr;22(2):324-33.

The volumes here are specially adapted for use with the MNI Linear
Registration Package (mni_autoreg).  Included in this package are the
following files:

     colin27_t1_tal_lin.mnc 
	a version of the average of 27 scans described above. This
        volume covers the whole brain (unlike the original Talairach
        atlas), and is sampled with 1mm cubic voxels
     colin27_t1_tal_lin_mask.mnc 
	a mask of the intra-cranial cavity of colin27.mnc, created
        manually.
     colin27_t1_tal_lin_headmask.mnc 
	a rough mask of the whole head, required for nonlinear mode
