Registration of PAM50 to T2star

SCT
1

Hi,

We are trying to register PAM50 template to our axial T2star data using sct_register_to_template. Since we need properly registered template/PAM50_levels.nii.gz, we use -lspinal flag and levels created by sct_label_utils.
Moreover, we use WM segmentation to take into account both GM and SC shape (flag -s-template-id 4).

Part of our pipeline is:

# Create WM segmentation from SC and GM masks
sct_maths -i sub-0001_ses-01_T2star_seg.nii.gz -sub sub-0001_ses-01_T2star_gmseg.nii.gz -o sub-0001_ses-01_T2star_wmseg.nii.gz
sct_maths -i sub-0001_ses-01_T2star_wmseg.nii.gz -o sub-0001_ses-01_T2star_wmseg.nii.gz -thr 0

# Create mid-vertebral levels. These labels are needed for template registration.
sct_label_utils -i sub-0001_ses-01_T2star_seg_labeled.nii.gz -vert-body 3,4,5,6,7 -o sub-0001_ses-01_T2star_labels_vert.nii.gz

# Register PAM50 template to t2star file using labels created in previous step
sct_register_to_template -i sub-0001_ses-01_T2star.nii.gz -s sub-0001_ses-01_T2star_seg_wmseg.nii.gz -lspinal sub-0001_ses-01_T2star_labels_vert.nii.gz -s-template-id 4 -ref subject -c t2s -param step=1,type=seg,algo=centermassrot,smooth=0:step=2,type=seg,algo=columnwise,smooth=0,smoothWarpXY=2

# Warp template without the white matter atlas
sct_warp_template -d sub-0001_ses-01_T2star.nii.gz -w warp_template2anat.nii.gz -a 0 -ofolder label_t2star

The resulting label_t2star/template/PAM50_levels.nii.gz however does not correspond with original vertebral levels, see images below.

T2star_seg_labeled and T2star_labels_vert (the cursor is placed to the red point with the value 3):

t2star_seg_labeled
t2star_seg_labeled1920×943 124 KB

template/PAM50_levels and T2star_labels_vert (the cursor is still placed to the same red point with the value 3, but PAM50_levels has value 2).

PAM50_levels
PAM50_levels1920×935 119 KB

In addition, PAM50_wm does not correspond well with the actual WM segmentation.

T2star:

t2star
t2star938×552 8.06 KB

T2star_gmseg:

t2star_gmseg
t2star_gmseg938×552 110 KB

T2star_wmseg:

t2star_wmseg
t2star_wmseg938×552 108 KB

template/PAM50_wm and T2star_gmseg:

t2star_PAM50wm_and_gmseg
t2star_PAM50wm_and_gmseg938×552 115 KB

Here we assumed that PAM50_wm would be alligned to T2star_wmseg.

SCT info:

sct_check_dependencies -short
--

SCT info:
- version: git-master-afdb05da537a75a34f3434f5512473f4e34f55bf*

Link to our data:

Thank you!
Jan and René

2

Hey Jan and René,

Thank you for the thorough description of the issue. As described in sct_register_to_template usage, more than two labels cannot be used with the flag -ref subject.

In your case, since you are dealing with highly isotropic voxels, I would suggest to only use two labels and keep the -ref subject flag.

I hope that helps!
Julien

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3

Hi Julien,

Thank you for your response. You are right! We missed the information that only two labels can be used with the flag -ref subject.

We have tried the registration with two labels and PAM50_levels are now correctly aligned.

PAM50_wm also looks much better.

Thank you!
Jan and René

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