NIfTI-1 Statistical parametric data
Other data intentions in NIfTI-1
NIfTI-1 is a somewhat new data format, proposed by the NIfTI DFWG as a short-term measure to facilitate inter-operation of functional MRI data analysis software packages. It is adapted from the widely used ANALYZETM 7.5 file format. The hope is that older non-NIfTI-aware software that uses the ANALYZE 7.5 format will still be compatible with NIfTI-1. NIfTI-1 uses the "empty space" in the ANALYZE 7.5 header to add several new features. These features are described in the current document.
To flag such a struct as being conformant to the NIFTI-1 spec, the last 4 bytes of the header must be either the C String ”ni1” or ”n+1”; in hexadecimal, the
4 bytes 6E 69 31 00 or 6E 2B 31 00 (in any future version of this format, the ’1’ will be upgraded to ’2’, etc.). Normally, such a ”magic number” or flag goes
at the start of the file, but trying to avoid clobbering widely-used ANALYZE 7.5 fields led to putting this marker last. However, recall that ”the last shall be
first” (Matthew 20:16).
If a NIFTI-aware program reads a header file that is NOT marked with a NIFTI magic string, then it should treat the header as an ANALYZE 7.5 structure.
”ni1” means that the image data is stored in the ”.img” file corresponding to the header file (starting at file offset 0).
”n+1” means that the image data is stored in the same file as the header information.
We recommend that the combined header+data filename should be ”.nii”. When the dataset is stored in one file, the first byte of image data is
stored at byte location (int)vox_offset in this combined file.
Most NIFTI-aware programs will only be able to handle a subset of the full range of datasets possible with this format. All NIFTI-aware programs should
take care to check if an input dataset conforms to the program’s needs and expectations (e.g., check datatype, intent_code, etc.). If the input dataset can’t
be handled by the program, the program should fail gracefully (e.g., print a useful warning; not crash).
This information is provided in the nifti-1.h code by Robert W. Cox (NIH)
.