NIfTI-1 Data Format

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Source Code, Documentation, Example Files and further information

Introduction

NIfTI-1 is adapted from the widely used ANALYZE™ 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 innovations are summarized in the OHBM poster [PDF], and include

Affine coordinate definitions relating voxel index (i,j,k) to spatial location (x,y,z);
Codes to indicate spatio-temporal slice ordering for FMRI;
"Complete" set of 8-128 bit data types;
Standardized way to store vector-valued datasets over 1-4 dimensional domains;
Codes to indicate data "meaning";
A standardized way to add "extension" data to the header;
Dual file (.hdr & .img) or single file (.nii) storage;

and many more. The goal is to foster interoperability at the file-exchange level between FMRI data analysis software packages. The authors of AFNI, BrainVoyager, FSL, and SPM have all committed to support this format for both input and output.

Note: The specification is now called NIfTI-1.1, with the finalization of the format for "extension" data, and a few other minor tweaks to the format that took place in early 2005.

Documentation

Summary

OHBM Poster (June 2004) [PDF] - A quick introduction to the NIfTI-1.1 Data Format.
Diagrams of the NIfTI-1.1 file structure [PDF] (Author: Hester Breman)

Formal Specification

NIfTI-1 header file - C header file that defines the NIfTI-1.1 format (Author: RW Cox)
Description of NIfTI-1.1 Fields with links to other useful cross references
Statistical Codes [PDF] - Documentation for NIfTI-1 statistical codes and sample C library for statistical distributions.
This file [PDF] shows how different FMRI software packages use the ANALYZE 7.5 fields in the .hdr file. (Deciding what was commonly used in FMRI data analysis was the first step in deciding which parts of the ANALYZE 7.5 format were "empty" and could be reclaimed for other purposes.)