questions > Voxel values 500 times higher with dcm2niix
Oct 23, 2016  12:10 PM | Pascal Pas
Voxel values 500 times higher with dcm2niix
After converting Philips DICOM with the october 2016 version of dcm2niix, voxel values in scans have increased by approximately 500 times. This does not happen when using the June 2015 version. This happens for both anatomical scans and EPI's.

Unfortunately I cannot find a download for the compiled 2015 linux version, so I'm now stuck with greatly inflated values; what is causing this? Or are previous versions available to download somewhere?

EDIT: I've discovered a change in the information displayed using spm_vol for the 2015 and 2016 converted images. For the June 2015 version the v_b.pinfo information is as follows:

5.46715497970581
0
352

However, for the 2016 version the following is displayed for a nifti converted from the same DICOM source:

2316.35791015625
0
352

Where:
V.pinfo - plane info for each plane of the volume.
% V.pinfo(1,:) - scale for each plane
% V.pinfo(2,:) - offset for each plane
% The true voxel intensities of the jth image are given
% by: val*V.pinfo(1,j) + V.pinfo(2,j)
% V.pinfo(3,:) - offset into image (in bytes).
% If the size of pinfo is 3x1, then the volume is assumed
% to be contiguous and each plane has the same scalefactor
% and offset.

So the scaling seems to be indeed off by a factor of (2316/5.5) 421.

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TitleAuthorDate
Voxel values 500 times higher with dcm2niix
Pascal Pas Oct 23, 2016
Chris Rorden Feb 19, 2017
Chris Rorden Oct 26, 2016
Felix Navarro Guirado Feb 9, 2017
Chris Rorden Feb 9, 2017
Felix Navarro Guirado Feb 10, 2017
Pascal Pas Oct 26, 2016
Chris Rorden Oct 25, 2016
Pascal Pas Oct 25, 2016