By default the BIAC processing daemon writes image data out as signed 16-bit integers. This data type has a maximum value of 32767. The recon sometimes writes out values greater than this value. If so, those values will be clipped to 32767. If you are seeing the "potentially-clipped" message, it is showing you the number of voxels that may be affected by this.
You can window the data in an image viewer to see which particular voxels are hitting this value. Also the following command:fmriqa_count --granularity voxel --ge 32767 /path/to/image/file
will give a list of voxel indices. The image file can be a .bxh file or .nii.gz or DICOM, or any other supported image format.
One solution is to ask Chris to have the daemon write out future image data as 32-bit floating point for your experiment. If you do this, the raw data will take twice as much disk space. Since data analysis accounts for most of the disk space you use, and since many data analyses write out floating point anyway, you may not notice the increased disk usage. But it's worth mentioning.
potentially-clipped voxels in QA
Posted - Sep 28 2012 : 1:36:33 PM
