Hi,

I'm getting the following warning message when trying to unpack epi data using to3d: "Slice-based center is different from mosaic center."

I only get this for some subjects who were run under a particular protocol in which all the epi parameters were constant across subjects. So, I'd be curious to know:

1.) Why might I get this error only for some subjects and not others and
2.) Is this something I should worry about?

I found two relevant posts on the message board:

[afni.nimh.nih.gov]
[afni.nimh.nih.gov]

In the first post, Daniel Glen says that this warning is only potentially a problem if your data is oblique, which mine is, which is what is leading me to worry.

From Daniel's reply to the second post, I get the impression that this warning is potentially a problem when the data is oblique because the mosaic center is used in computing how oblique a given data set is, and an inconsistency with the slice-based center indicates that the obliquity calculation could be incorrect (or something like that). I also get the impression that you should only worry about this if you're unhappy with the alignment of the epis with the anatomy, post-3dAllineate (i.e., align_epi_anat) or 3dvolreg.

Is this right?

Thanks!
-Joe

Here's the command I'm using:
"$ to3d -prefix unpackedFunc -time:zt nSlices nTRs 0 alt+z firstEpiFile"

And here's the relevant output from to3d:

++ to3d: AFNI version=AFNI_2008_07_18_1710 (Sep 10 2008) [64-bit]
++ Authored by: RW Cox
++ Counting images: total=8784 2D slices
++ DICOM NOTICE: 6x6 Siemens Mosaic of 36 96x96 images in file dicom/947000-000005-000001.dcm
++ Data detected to be oblique
++ Each 2D slice is 96 X 96 pixels
++ Voxel dimensions: 3.0000 X 3.0000 X 3.4800 mm
++ Image data type = short
++ Reading images: ++ DICOM NOTICE: 6x6 Siemens Mosaic of 36 96x96 images in file dicom/947000-000005-000002.dcm
++ DICOM NOTICE: no more Siemens Mosaic messages will be printed
..........................................
*+ WARNING: Slice-based center is different from mosaic center
*+ WARNING: Origin computation of obliquity may be incorrect
Mosaic Center: -0.316288 -13.2615 -4.00681
Slice-based Center: -0.333387 -13.2618 -4.00796
Mosaic Center: -0.316288 -13.2615 -4.00681
Origin Coordinates: -142.204 -167.943 -20.2511