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nifti1.h header documentation

pixdim[i] = voxel width along dimension #i, i=1..dim[0] (positive) - cf. ORIENTATION section below for use of pixdim[0] - the units of pixdim can be specified with the xyzt_units field (also described far below).

/---------------------------------------------------------------------------/ /* UNITS OF SPATIAL AND TEMPORAL DIMENSIONS: ---------------------------------------- The codes below can be used in xyzt_units to indicate the units of pixdim. As noted earlier, dimensions 1,2,3 are for x,y,z; dimension 4 is for time (t). - If dim[4]=1 or dim[0] < 4, there is no time axis. - A single time series (no space) would be specified with - dim[0] = 4 (for scalar data) or dim[0] = 5 (for vector data) - dim[1] = dim[2] = dim[3] = 1 - dim[4] = number of time points - pixdim[4] = time step - xyzt_units indicates units of pixdim[4] - dim[5] = number of values stored at each time point

Bits 0..2 of xyzt_units specify the units of pixdim[1..3] (e.g., spatial units are values 1..7). Bits 3..5 of xyzt_units specify the units of pixdim[4] (e.g., temporal units are multiples of 8).

The toffset field can be used to indicate a nonzero start point for the time axis. That is, time point #m is at t=toffset+m*pixdim[4] for m=0..dim[4]-1.


  1. B.: Method 2 uses a factor qfac which is either -1 or 1; qfac is stored in the otherwise unused pixdim[0]. If pixdim[0]=0.0 (which should not occur), we take qfac=1. Of course, pixdim[0] is only used when reading a NIFTI-1 header, not when reading an ANALYZE 7.5 header.

Created by Alex Clark
Last modified 2005-04-14 18:42

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