[Insight-users] is DICOM volume origin calculation correct?

[Bill Lorensen]

ITK uses a right handed coordinate system. That is why in this case, the
last slice is the origin slice. At last that's what I recall.



On Thu, Aug 8, 2013 at 1:10 PM, marianabb <marianabb at gmail.com> wrote:

> Hello,
>
> I am using ITK-4.3.2 to create a volume from a stack of DICOM single-frame
> images of the heart.
>
> Most of the code is taken from the example DicomSeriesReadImageWrite2.cxx,
> and the basics work, but I'm confused about whether the volume origin
> produced is correct.
>
> The volume is composed of 14 slices, with spacing [1.0, 1.0, 8.0], the
> first
> and last slices have the following origins (Image Position Patient, DICOM
> tag 0020,0032):
> - First slice: 42.021, -174.562, 159.592
> - Last slice: -27.608, -102.908, 188.461
>
> The resulting file created with ITK has the last slice IPP as the image
> origin, but if I open the original DICOM files with Slicer or Matlab the
> resulting image has the first slice IPP as the origin.
>
> I thought that maybe ITK was just using the IPP of the last file it read,
> but if I read the slices in the opposite order (last slice as first as so
> on) the resulting origin is still the same as before.
>
> I understand also that Slicer and DICOM files use the top-left voxel as the
> origin, while ITK uses the bottom-left voxel, but this still doesn't
> explain
> using the last slice IPP.
>
> Any thoughts on this matter would be of great help.
>
> Thanks!
> --
> Mariana
>
>
>
> --
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