[ITK-users] [ITK] Is image direction taken into account during registration?

[Matt McCormick]

Hi Vincent,

ITK reads in and accounts for directions cosines for you in the
registration process.  Every ITK Image has a Direction matrix
associated with it.  Hans Johnson has made sure this is described in
the latest versions of the ITK Software Guide. [1].

Thanks,
Matt

[1] http://itk.org/ItkSoftwareGuide.pdf

On Mon, May 5, 2014 at 2:46 AM, vincent ngai <vincent.ngai at gmail.com> wrote:
> Hi all, apologies if this has been asked, but a cursory search of image
> direction and registration did not turn up what i was looking for.
>
> Specifically I am trying to find out whether image direction is required for
> proper registration.
>
> From what I understand image direction comes from the DICOM directional
> cosines. So say for sagittal images, image origin correspond to the the top
> left pixel centre in world space, and the x index ideal direction is [LPS
> +ve Y]( 0, 1, 0 )  and y index direction is [LPS -ve Z] ( 0, 0, -1 ). The
> direction cosines comes from the table tilt of the scanner and the scanner's
> sampling space remains fixed and cartesian as the LPS coordinate system, and
> actual orientation of the patient's head may deviate from the table's
> directions.
>
> If my understanding of the above is correct(?) Then should the images to be
> used for registration have their direction cosines replaced with the given
> view's( sagittal, coronal etc ) ideal directions? I have read its dangerous
> to change the image direction, but in this case I'm preserving the view's
> orientation and ensuring that the registration process is comparing 2
> similarly oriented spaces with differently oriented samples (i.e head tilt,
> multimodal ).
>
> What I am trying to do is based on the different DICOM scans e.g sagittal,
> coronal, bring both images into the common LPS coordinate system, then
> perform the registration in that space. And it would seem that preserving
> the original direction cosines doesn't make any sense, since they do not
> infer the actual scanner's sampling space.
>
>
> Thank you.
>
>
> --
> Regards,
> Vincent
>
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