NIfTI-1 Data Format
File type: Various data file
Files with nii file extension use the NIfTI-1 Data Format, a standard for storing neuroimaging data.
Neuroimaging applications use these files to store image data together with information needed to interpret the images.
File type category:
Various data file
Date updated: October 17, 2026
Record marked as obsolete and not updated for a long time.
NIfTI-1 was developed by the Neuroimaging Informatics Technology Initiative for exchanging neuroimaging data. It was adapted from the widely used ANALYZE 7.5 data format.
A nii file normally contains both the image header and the voxel data in one file. The header can describe the image dimensions, voxel data type, voxel sizes, spatial orientation and other information required by neuroimaging software.
NIfTI-1 is platform-independent and is supported by neuroimaging applications on Windows, macOS and Linux. It is an older specification, but remains widely used; NIfTI-2 is available for datasets that require capabilities beyond NIfTI-1.
Open a nii file with a NIfTI-aware neuroimaging application such as 3D Slicer or MRIcroGL. These applications are available for Windows, macOS and Linux. Software libraries such as NiBabel can also read NIfTI-1 files for Python-based analysis.
NIfTI-1 files can be imported or exported by neuroimaging software such as 3D Slicer and FSL. Neuroimaging software can also convert DICOM imaging data to NIfTI.
Conversion may lose spatial orientation, scaling information or other metadata, so the original file should be retained when possible.
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