Laterality issue on fMRI image
The laterality issue: different software will interpret fMRI images in different way (mainly refer to right/left side display), so will the functions offered by them. NIFTI toolbox provides series explanations on the issued. Here are some notes.
Definition of LEFT and RIGHT
If the display does not have labels, we define LEFT as the Left-Hand-Side
of the Axial view, and RIGHT as the Right-Hand-Side of the Axial view.
RAS (neurological convention): left cerebral hemisphere is at LEFT and
right cerebral hemisphere is at RIGHT;
LAS (radiological convention): right cerebral hemisphere is at LEFT and
left cerebral hemisphere is at RIGHT;
If the display has labels, note will be added to bring your attention.
Laterality case in common softwares
| Software | Input format | Input laterality | Input display | Output format | Output laterality |
|---|---|---|---|---|---|
| SPM5/later | ANALYZE | RAS | LAS | NIfTI | LAS |
| SPM5/later | ANALYZE | LAS | RAS | NIfTI | RAS |
| MRIcro | ANALYZE | RAS | RAS | ANALYZE | RAS |
| MRIcro | ANALYZE | LAS | LAS | ANALYZE | LAS |
| MRIcron | ANALYZE | RAS | RAS | NIfTI | RAS |
| MRIcron | ANALYZE | LAS | LAS | NIfTI | LAS |
| load/save/view_nii | ANALYZE | RAS | RAS | NIfTI | RAS |
| load/save/view_nii | ANALYZE | LAS | LAS | NIfTI | LAS |
| load/save_untouch_nii | ANALYZE | RAS | N/A | ANALYZE | RAS |
| load/save_untouch_nii | ANALYZE | LAS | N/A | ANALYZE | LAS |
Interpret laterality using load_nii command
- NIfTI toolbox never saves any file with sform = qform = 0. When you see that sform = qform = 0 in the structure that is loaded by "load_nii.m", it only means that the affine matrix has been properly interpreted. As a matter of fact, the file written by "save_nii.m" is always a NIfTI file with sform = 1 and qform = 0, and you can always check the real header information stored in any NIfTI (ANALYZE) file by using "load_untouch_nii.m". In other words, you can never save your data to a NIfTI file with sform = qform = 0.
If you want to save your data to an ANALYZE format, you can do so by using "save_untouch_nii.m". In that case, there is neither sform nor qform in the
ANALYZE header. - Many other software assume that ANALYZE files are in neurological convention (RAS). Because there is really no orientation information stored in ANALYZE header, the laterality of an ANALYZE file is all based on the assumption.
