Hi Don,
these matrices are all very tricky. Try looking at:
ftp://surfer.nmr.mgh.harvard.edu/transfer/outgoing/flat/greve/fscoordinates.ppt
I don't the the lta is documented in there explicitly, but it has the same interpretation as the MNI xfm.
doug
Don Hagler wrote:
Hi Bruce,
I thought that the talairach.lta file was not actually registering to talairach, but instead to the atlas in advance of the nonlinear registration.
When I load the lta file in matlab (with read_lta.m) and then resample a volume using that registration matrix, the brain goes to a different place for each subject if I assume that the registration matrix is from subject to atlas. If I assume that the matrix is instead from atlas to subject, then the resampled brain goes to roughly the same location for different subjects.
Don
From: Bruce Fischl fischl@nmr.mgh.harvard.edu To: Don Hagler dhaglerjr@hotmail.com CC: freesurfer@nmr.mgh.harvard.edu Subject: Re: [Freesurfer] talairach.lta Date: Mon, 11 Jun 2007 23:44:20 -0400 (EDT)
Hi Don,
I believe it is from subject ras to talairach ras, and it is definitely affine (not just rigid). The .lta format is generic enough that it will list what type of transform it is (e.g. voxel or ras). Here are most of the relevant types: #define LINEAR_VOX_TO_VOX 0 #define LINEAR_VOXEL_TO_VOXEL LINEAR_VOX_TO_VOX #define LINEAR_RAS_TO_RAS 1 #define LINEAR_PHYSVOX_TO_PHYSVOX 2 #define TRANSFORM_ARRAY_TYPE 10 #define MORPH_3D_TYPE 11 #define MNI_TRANSFORM_TYPE 12 #define MATLAB_ASCII_TYPE 13 #define LINEAR_CORONAL_RAS_TO_CORONAL_RAS 21 #define LINEAR_COR_TO_COR LINEAR_CORONAL_RAS_TO_CORONAL_RAS
cheers, Bruce
On Mon, 11 Jun 2007, Don Hagler wrote:
Can someone please explain what transformation matrix is contained in talairach.lta?
Is this the registration matrix from atlas to subject or subject to atlas?
Also, is this matrix for rigid body registration only, or does it have the affine registration?
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