[Insight-users] DICOM reader

[Mathieu Malaterre]

Salut Delphine,

On Tue, Apr 21, 2009 at 10:52 AM, Delphine Ribes <delphine.ribes at epfl.ch> wrote:
> Dear itk users,
>
> I've implemented a DICOM reader and I wanted to compare it with itk DICOM
> reader.
> The output of the DICOM reader I've implemented is an itk Image.
>
> I have some MPRAGE saggital data. First I've realized that I was not reading my
> data the same direction as itk.
> Me from 1 to 160
> itk from 160 to 1
> Is it a convention?

What is '1' ? what is '160' ? My cristal ball is telling me you are
refering to Instance Number, right ? Since this is a DICOM Type 3,
this cannot be used to order the individual DICOM slice. Instead the
only other information you can use reliably in cross-sectional
aquisition (CT, MR...) is the pair Image Orientation (Patient) (IOP)
and Image Positon (Patient) (IPP). Then the ordering is defined along
this normal, with a positive spacing.

It is described as 'jolinda' algorithm in gdcm. I could find this old ref:
http://www.itk.org/pipermail/insight-users/2003-September/004762.html

> In addition, when I write for example a .mhd file, and I read directly the
> header.
> The Tag : TransformMatrix is = to 0 0 -1 1 0 0 0 -1 0
> or it should be = to TransformMatrix = 0 1 0 0 0 -1 -1 0 0 as for the itk DICOM
> reader.
>
> In "My" DICOM reader, I get the direction from the DICOM header tag :
> 0x0020,0x0037
> For direction 0 and 1 and then I do a cross product to get direction 2.
> I suppose there is something I miss understood concerning the image direction in
> itk.
> I should obtain the same as the itk dicom reader as output !

I believe we are doing the same. could there be an issue in inverting
columns and rows ?

HTH
-- 
Mathieu