Coregistration is only supposed to do a rigid-body registration (ie rotations
and translations). Provided the voxel sizes are set correctly, then this
should be all that is needed for within subject registration of the head.
Scaling parameters are therefore all set to one.
Best regards,
-John
On Thursday 24 July 2008 19:47, Henrique Amaral wrote:
> Hi SPMers,
>
> I've used the SPM2 to perform coregister in SPECT images. I am using the
> "Mutual Information" cost function, and the "Trilinear" interpolation, with
> "Wrap X, Y and Z", and "don't mask images".
> The rotations and translations are perform perfectly, but, the scaling
> isn't work, once that the image object don't wrap.
>
> I'm storing the parameters of the coregister (i get the P vector in rotine
> spm_matrix) and during the coregister the scaling parameters didn't change
> the value, remaining invariable in 1:
>
> function [A] = spm_matrix(P)
> % returns an affine transformation matrix
> % FORMAT [A] = spm_matrix(P)
> % P(1) - x translation
> % P(2) - y translation
> % P(3) - z translation
> % P(4) - x rotation about - {pitch} (radians)
> % P(5) - y rotation about - {roll} (radians)
> % P(6) - z rotation about - {yaw} (radians)
> % P(7) - x scaling
> % P(8) - y scaling
> % P(9) - z scaling
> % P(10) - x affine
> % P(11) - y affine
> % P(12) - z affine
>
> q = [0 0 0 0 0 0 1 1 1 0 0 0];
> P = [P q((length(P) + 1):12)];
>
> T = [1 0 0 P(1);
> 0 1 0 P(2);
> 0 0 1 P(3);
> 0 0 0 1];
>
> R1 = [1 0 0 0;
> 0 cos(P(4)) sin(P(4)) 0;
> 0 -sin(P(4)) cos(P(4)) 0;
> 0 0 0 1];
>
> R2 = [cos(P(5)) 0 sin(P(5)) 0;
> 0 1 0 0;
> -sin(P(5)) 0 cos(P(5)) 0;
> 0 0 0 1];
>
> R3 = [cos(P(6)) sin(P(6)) 0 0;
> -sin(P(6)) cos(P(6)) 0 0;
> 0 0 1 0;
> 0 0 0 1];
>
> Z = [P(7) 0 0 0;
> 0 P(8) 0 0;
> 0 0 P(9) 0;
> 0 0 0 1];
>
> S = [1 P(10) P(11) 0;
> 0 1 P(12) 0;
> 0 0 1 0;
> 0 0 0 1];
>
> A = T*R1*R2*R3*Z*S; % A is the affine transformation matrix.
>
> Why the scaling don't work in coregister?
>
> Thanks
>
> Henrique Amaral
> Hospital das Clínicas
> University Of São Paulo - Ribeirão Preto - Brazil
