[Insight-users] direction cosines question

[Luca Pamparana]

Hi Mathieu,

Thanks for the link. A lot of my doubts have been cleared. It seemed I had
misunderstood the whole concept.

I have a couple of questions though that I hope someone could help me with:

- The patient coordinate system. How is that determined? Is it relative to
the scanner?

- I saw that the normal along a slice could be determined from the direction
cosines as follows:

normal[0] = cosines[1]*cosines[5] - cosines[2]*cosines[4];
normal[1] = cosines[2]*cosines[3] - cosines[0]*cosines[5];
normal[2] = cosines[0]*cosines[4] - cosines[1]*cosines[3];

Can someone explain how this works? I know that the cross product of the
unit vector along x axes and the unit vector along y axes willpoint towards
the z axes but cannot figure out how the above relationships translate to
that. If someone can explain this to me, I would be grateful.

Thanks a lot.

Luca

On 6/4/07, Mathieu Malaterre <mathieu.malaterre at gmail.com> wrote:
>
> Hi Luca,
>
>   I would suggest you to read:
>
> http://www.itk.org/Wiki/Proposals:Orientation#Some_notes_on_the_DICOM_convention_and_current_ITK_usage
> and
> PS 3.3 - 2007, section:
> C.7.6.2.1.1 Image Position And Image Orientation
>
> HTH
> -Mathieu
>
> On 6/4/07, Luca Pamparana <luca.pamparana at gmail.com> wrote:
> > Hi everyone,
> >
> > I am pretty new to medical imaging and trying to learn some vector
> > mathematics behind it. I have a question about the "Image Orientation
> > Patient" tag. It says this tag gives the direction cosines for the rows
> and
> > colums for the 3 axes.
> >
> > Now my question is, rows and colums direction cosines wrt to which
> plane??
> >
> > Also, each slice has this tag and a slice is just a 2D image. So, how
> come
> > we get 3 pairs of direction cosine values?
> >
> > I am sorry if these questions are very stupid. I would be really
> grateful if
> > someone can clarify these doubts for me...
> >
> > Thanks a lot,
> >
> > Luca
> >
> > _______________________________________________
> > Insight-users mailing list
> > Insight-users at itk.org
> > http://www.itk.org/mailman/listinfo/insight-users
> >
> >
>
>
> --
> Mathieu
>
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