Introduction

The NIfTI committee, in conjunction with public discussion on the NITRC forum, have created a final version for the NIfTI-2 format that is a very simple extension of the current NIfTI-1 format, but updated to allow 64-bit storage and addressing for large images and matrices.

It is intended that this format:

• will enable the storage of large images and matrices, with all dimensions being coded by 64-bit integers rather than the current limitation of 16-bit signed integers (which currently gives a restrictive 32767 size limit in each dimension)
• will be very simple to implement and update software (a couple of hours coding or less generally)
• contains the same information and logic as a NIfTI-1 file (no new fields and all current fields still retained)
• will support the existing file formats and naming: a .nii single-file, a .hdr/.img file-pair and their gzipped versions
• has a very simple test (see below) to determine if the file is NIfTI-1 or NIfTI-2
• does not replace NIfTI-1 in the short term but is supported alongside it

Documentation

• Formal Specification

• NIfTI-2 header file - C header file that defines the NIfTI-2 format (not final)

• Description of NIfTI-2 Fields
• description matches that of the NIfTI-1.1 Fields of the NIfTI-1 header file
  
• field types and field order have been altered
  
• extentions match those of NIfTI-1.1 when the extender bytes are 1 0 0 0
  
• in the future, extenders may be added using other byte sequences
  

Test Data Sets

• Test Data - A few valid structural (3D) files in NIfTI-2 format.

Supporting Software

• AFNI, BrainVisa, BrainVoyager, Caret, Connectome Workbench, Fiswidgets, FreeSurfer, FSL, ITK, LONI-DIRAC, Mango, MRIcron, NiBabel, R, SPM and TractoR have all agreed to support the NIfTI-2 version in their upcoming releases, but that NIfTI-1 will remain a default output, or a configurable default, in the short-term

• the sourceforge supporting libraries in niftilib will be updated so that they seemlessly support both NIfTI-1 and NIfTI-2

• conversion utilities to and from NIfTI-1 will be made available via sourceforge as well as in some of the software packages mentioned above