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Hello,

I am currently working on registering MRI and PET data from the ADNI dataset, processed using our custom preprocessing pipeline, to the fsaverage template. My goal is to align both the MRI and PET data to the fsaverage template.

To achieve this, I followed these steps:

Step 1: I used mri_coreg to create an LTA file for registering the MRI data to the fsaverage template. Then, I used mri_vol2vol to perform the registration of the MRI data to the fsaverage template. Commands Used: mri_coreg --mov $MRI_PATH --targ $FREESURFER_HOME/subjects/fsaverage/mri/brain.mgz --reg ${OUTPUT_DIR}/mri${num}_reg.lta mri_vol2vol --mov $MRI_PATH --targ $FREESURFER_HOME/subjects/fsaverage/mri/brain.mgz --reg ${OUTPUT_DIR}/mri${num}_reg.lta --o ${OUTPUT_DIR}/mri${num}_to_atlas.nii.gz

Step 2: I used the LTA file generated in Step 1 and applied mri_vol2vol to register the PET data to the MRI data. Commands Used: mri_vol2vol --mov $PET_PATH --targ ${OUTPUT_DIR}/mri${num}_to_atlas .nii.gz --reg ${OUTPUT_DIR}/mri${num}_reg.lta --o ${OUTPUT_DIR}/pet${num}_to_atlas.nii.gz

However, when visualizing the results using Freeview, I noticed that the registration of both the MRI and PET data to the fsaverage template is not accurate. (The MRI and PET data were successfully co-registered.)

I have attached some images of the results and the output from the mri_info command for your reference.

# mri_info results ## T1w MRI niiRead(): detected input as 64 bit double, reading in as 32 bit float Volume information for {my_mri_data} type: nii dimensions: 128 x 128 x 128 voxel sizes: 1.000000, 1.000000, 1.000000 type: FLOAT (3) fov: 128.000 dof: 1 xstart: -64.0, xend: 64.0 ystart: -64.0, yend: 64.0 zstart: -64.0, zend: 64.0 TR: 0.00 msec, TE: 0.00 msec, TI: 0.00 msec, flip angle: 0.00 degrees nframes: 1 PhEncDir: UNKNOWN FieldStrength: 0.000000 ras xform present xform info: x_r = -1.0000, y_r = -0.0000, z_r = 0.0000, c_r = -13.0000 : x_a = -0.0000, y_a = 1.0000, z_a = -0.0000, c_a = 16.5000 : x_s = 0.0000, y_s = 0.0000, z_s = 1.0000, c_s = 11.5000 Orientation : LAS Primary Slice Direction: axial

voxel to ras transform: -1.0000 -0.0000 0.0000 51.0000 -0.0000 1.0000 -0.0000 -47.5000 0.0000 0.0000 1.0000 -52.5000 0.0000 0.0000 0.0000 1.0000

voxel-to-ras determinant -1

ras to voxel transform: -1.0000 -0.0000 -0.0000 51.0000 -0.0000 1.0000 -0.0000 47.5000 -0.0000 -0.0000 1.0000 52.5000 -0.0000 -0.0000 -0.0000 1.0000

## brain.mgz Volume information for /usr/local/freesurfer/7.4.1/subjects/fsaverage/mri/brain.mgz type: MGH dimensions: 256 x 256 x 256 voxel sizes: 1.000000, 1.000000, 1.000000 type: UCHAR (0) fov: 256.000 dof: 0 xstart: -128.0, xend: 128.0 ystart: -128.0, yend: 128.0 zstart: -128.0, zend: 128.0 TR: 0.00 msec, TE: 0.00 msec, TI: 0.00 msec, flip angle: 0.00 degrees nframes: 1 PhEncDir: UNKNOWN FieldStrength: 0.000000 ras xform present xform info: x_r = -1.0000, y_r = 0.0000, z_r = 0.0000, c_r = 0.0000 : x_a = 0.0000, y_a = 0.0000, z_a = 1.0000, c_a = 0.0000 : x_s = 0.0000, y_s = -1.0000, z_s = 0.0000, c_s = 0.0000

talairach xfm : /usr/local/freesurfer/7.4.1/subjects/fsaverage/mri/transforms/talairach.xfm Orientation : LIA Primary Slice Direction: coronal

voxel to ras transform: -1.0000 0.0000 0.0000 128.0000 0.0000 0.0000 1.0000 -128.0000 0.0000 -1.0000 0.0000 128.0000 0.0000 0.0000 0.0000 1.0000

voxel-to-ras determinant -1

ras to voxel transform: -1.0000 -0.0000 -0.0000 128.0000 -0.0000 -0.0000 -1.0000 128.0000 -0.0000 1.0000 -0.0000 128.0000 -0.0000 -0.0000 -0.0000 1.0000

Could you please help me identify any potential issues with my approach or the commands I used? I would greatly appreciate any guidance you can provide.

Thanks a lot!

Best regards, Junho Moon