| Can you telle me please the meaning of X ,Y, Z, when i use the mutual
| information registration method?
| I have used a PET cardiac images and I want to compare the angles that
| I've imposed with the results of SPM.
The matrix multiplication displayed after running mutual information
coregistration, shows a mapping from voxels in the stationary image,
to those in the image that was rotated and translated. This mapping
is derived from a series of rotations and translations (and zooms where
voxel sizes differ between the images). The X, Y and Z refer to voxel
co-ordinates in the stationary image, whereas X1, Y1 and Z1 refer to
co-ordinates in the other one. The matrix can be decomposed into a
series of translations, rotations, zooms and shears using the spm_imatrix
function. For example, if the display says:
X1 = 0.9998*X - 0.0175*Y + 0*Z - 10.0000
Y1 = 0.0174*X + 0.9997*Y + 0.0175*Z + 0
Z1 = -0.0003*X - 0.0174*Y + 0.9998*Z + 10.0000
Then typing:
M = [0.9998 -0.0175 0 -10.0000
0.0174 0.9997 0.0175 0
-0.0003 -0.0174 0.9998 10.0000
0 0 0 1.0000];
spm_imatrix(M)
should produce:
ans =
Columns 1 through 7
-10.0000 0 10.0000 0.0175 0 -0.0175 1.0000
Columns 8 through 12
1.0000 1.0000 0.0000 0 0
which describes translations in the x and z directions of -10 and 10 voxels
and rotations about the x and z axes (pitch and yaw) of 1 and -1 degrees
(0.0175 and -0.0175 radians). The parameters are probably better explained
if you type:
help spm_matrix
All the best,
-John
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