[Insight-users] GE diffusion data - extract orientation from DICOM header

[Mathieu Malaterre]

Hi Michael,

On Thu, Jan 8, 2009 at 11:40 PM, Michael Scheel
<mscheel at eyecarecentre.org> wrote:
> Hi everybody,
>
> i have a question if anybody can give me some advise on a problem with a DTI
> series acquired on a General Electric Signa 3T.
> I have the DICOM dataset and the file for the gradient directions in the
> Scanner Coordinates.
> To avoid artefacts we aquired the data parallel to a plane (frontal sinus -
> cerebellum) - that gives quite a big angulation of the xy-plane.
>
> What I need to do is to take into account this angulation and correct the
> gradient-direction-file.
> My problem is that I don't know how to extract the amount of angulation from
> the DICOM header.

See the wiki page:

http://wiki.na-mic.org/Wiki/index.php/NAMIC_Wiki:DTI:DICOM_for_DWI_and_DTI#Private_vendor:_GE

> So I guess my question boils down to:
>
> How do I extract the angulation parameters from the DICOM header and use it
> to correct the gradient-direction-file?
>
> Here is what the header says:
> ....
> ImagePositionPatient (0020,0032) -129.492\-147.271\35.8859
> value -129.492
> value -147.271
> value 35.8859
> ImageOrientationPatient (0020,0037) 1\-0\0\-0\0.844841\-0.535018
> value 1
> value -0
> value 0
> value -0
> value 0.844841
> value -0.535018
> .....
>
> I just don't know how to translate this, especially why are there 6 values
> for the orientation when there are 3 planes that can be angulated?


That's the Direction Cosines of the plane. The 6 values are 2 vector
in 3D spaces. They are normalized and their cross product gives you
the 3rd vector.

See DICOM PS 3.3-2008, C.7.6.2.1.1 Image Position And Image Orientation

HTH
-- 
Mathieu