[Insight-users] direction cosines question

[Luis Ibanez]

Hi Luca,

You may want to read the following Wiki page:

   http://www.itk.org/Wiki/Proposals:Orientation

In particular the section:

http://www.itk.org/Wiki/Proposals:Orientation#Some_notes_on_the_DICOM_convention_and_current_ITK_usage


Regards,


   Luis


--------------------
Luca Pamparana wrote:
> 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 
> <mailto: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
>     <mailto: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
>      >
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>      >
>      >
> 
> 
>     --
>     Mathieu
> 
> 
> 
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