Hi,

I've used `bbregister` to generate a transform `bold2T1.lta` from `bold.nii` to 
`T1.mgz` (assume we have a `T1.nii` as well for the sake of ANTs). 

The following produces a well-aligned output:

    mri_convert --apply_transform bold2T1.lta bold.nii bold_space-T1.nii

As does the following:

    lta_convert --inlta bold2T1.lta --outfsl bold2T1.mat
    c3d_affine_tool -ref T1.nii -src bold.nii bold2T1.mat -fsl2ras -oitk 
bold2T1.txt
    antsApplyTransforms -i bold.nii -r T1.nii -o bold_space-T1.nii -t 
bold2T1.txt

However, if one skips the FSL step, the registration is quite far off:

    lta_convert --inlta bold2T1.lta --outitk bold2T1.txt
    antsApplyTransforms -i bold.nii -r T1.nii -o bold_space-T1.nii -t 
bold2T1.txt

Comparing the ITK transform files:

LTA-FSL-ITK

    #Insight Transform File V1.0
    #Transform 0
    Transform: MatrixOffsetTransformBase_double_3_3
    Parameters: 0.9895096215486424 0.011126830936108464 -0.00042204653562094823 
-0.01079971161879626 0.872329255299452 -0.42602926756857834 
-0.004755964529051335 0.42420535065804454 0.8878552541301569 
-1.3066136395454464 -45.60342165876236 -43.10584860730749
    FixedParameters: 0 0 0


LTA-ITK

    #Insight Transform File V1.0
    #Transform 0
    Transform: AffineTransform_double_3_3
    Parameters: 0.98950976133346558 0.011126830242574215 
-0.00042204943019896746 -0.010799713432788849 0.87232941389083862 
-0.42602935433387756 -0.0047559700906276703 0.42420542240142822 
0.88785547018051147 -2.2848172187805176 -2.9065067768096924 11.744022369384766
    FixedParameters: 0 0 0


To 5 significant digits, these are the same, except the last three 
(translation) parameters. And the `AffineTransform_double_3_3` is different 
from `MatrixOffsetTransformBase_double_3_3`, though I'm not sure whether this 
has any effect.

Here is the original LTA:

    type      = 1 # LINEAR_RAS_TO_RAS
    nxforms   = 1
    mean      = 0.0000 0.0000 0.0000
    sigma     = 1.0000
    1 4 4
    1.010462999343872e+00 -1.063966564834118e-02 4.625014495104551e-03 
-2.332115173339844e+00 
    1.228639855980873e-02 9.293417930603027e-01 -4.459420144557953e-01 
2.507942199707031e+00 
    4.575361963361502e-04 4.440840482711792e-01 9.132194519042969e-01 
-1.201664733886719e+01 
    0.000000000000000e+00 0.000000000000000e+00 0.000000000000000e+00 
9.999998807907104e-01 
    src volume info
    valid = 1  # volume info valid
    filename = 
/scratch/fmriprep_wf/single_subject_02_wf/func_preproc_task_short_wf/bold_reg_wf/bbreg_wf/bbregister/uni_masked_xform.nii.gz
    volume = 64 64 34
    voxelsize = 3.125000000000000e+00 3.125000000000000e+00 
4.000000000000000e+00
    xras   = -1.000000000000000e+00 0.000000000000000e+00 0.000000000000000e+00
    yras   = 0.000000000000000e+00 1.000000000000000e+00 0.000000000000000e+00
    zras   = 0.000000000000000e+00 0.000000000000000e+00 1.000000000000000e+00
    cras   = -1.090248107910156e+00 -1.071614074707031e+01 1.619928741455078e+01
    dst volume info
    valid = 1  # volume info valid
    filename = 
/scratch/fmriprep_wf/single_subject_02_wf/anat_preproc_wf/t1_merge/sub-02_T1w_template.nii.gz
    volume = 160 192 192
    voxelsize = 1.000000000000000e+00 1.333333015441895e+00 
1.333333015441895e+00
    xras   = 1.000000000000000e+00 0.000000000000000e+00 0.000000000000000e+00
    yras   = 0.000000000000000e+00 1.000000000000000e+00 0.000000000000000e+00
    zras   = 0.000000000000000e+00 0.000000000000000e+00 1.000000000000000e+00
    cras   = -3.000000000000000e+00 2.999969482421875e+00 -8.000030517578125e+00
    subject sub-02
    fscale 0.100000


If it would be useful, I can provide any relevant images for testing.

--
Chris Markiewicz
Center for Reproducible Neuroscience
Stanford University


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