[vtkusers] [python-medphys] Re: [Insight-users] [Gdcm2] Matching CT and RT dose coordinates

[Jothy]

You are absolutely corrcet - the data set is from dicompyler.

Thanks for providing the data set as part of the dicompyler.

Jothy

On Thu, Feb 24, 2011 at 6:16 AM, Adit Panchal <apanchal at bastula.org> wrote:

> The dataset looks like the test data from dicompyler. If that is the
> case, then I know for a fact that the CT images and the dose planes
> are coincident, since they I exported them from Varian Eclipse.
>
> The only issue I can think of is that the incorrect rendering has
> something to do with the pixel spacing of [1.074, 1.074] vs [2.5, 2.5]
> for the dose grid and the CT data respectively along with an incorrect
> origin. The top right corner of the dose plane is almost at the center
> of the CT image, which needs to be transposed. The same test data
> renders correctly in dicompyler.
>
> Adit
>
> On Wed, Feb 23, 2011 at 23:39, Karthik Krishnan
> <karthik.krishnan at kitware.com> wrote:
> > As others already mentioned, you need to re-inteprolate the dose volume
> onto
> > the CT data. To do that you must use the grid frame offset vectors.
> >
> > For all dose images I've encountered, the spacing between these grid
> planes
> > (as specified by the grid frame offset vectors) is a constant, but this
> need
> > not always be the case. If you want to be thorough you need to account
> for
> > this. Several folks don't (for instance below is an excerpt from Varian's
> > conformance statement):
> >
> > "Dose Plane Spacing:
> > If Grid Frame Offset Vector (3004,000C) is present, it must contain
> offset
> > values yielding equally spaced dose planes. Therefore, those values
> follow
> > option a. in C.8.8.3.1 in Part 3 of [1]. RT Dose Instances having
> unequally
> > spaced dose planes are not supported."
> >
> > So for this specific case, where the grid plane spacing is the same, you
> > could use the using the starting grid frame offset vector and the grid
> plane
> > spacing and use the itk::ResampleImageFilter. Simply use GDCM to convert
> the
> > images to MHD. Then set the spacing and origin to match the starting grid
> > plane offset vector and the grid plane spacing..
> >
> > If you load the images in to 3DSlicer, I believe they should already be
> > re-interpolated and placed in the right coordinate system.
> >
> >
> > --
> > karthik
> >
> >
> >
> >
> > On Thu, Feb 24, 2011 at 2:36 AM, Mark Roden <mmroden at gmail.com> wrote:
> >>
> >> Hi Jothy,
> >>
> >> What are the direction cosines?
> >>
> >> There is a problem where VTK reinterprets the direction cosines to
> >> change the directions of images produced by the dicom reader.
> >>
> >> DICOM specifies that the image patient position is always the upper
> >> left pixel (if you look at the image as a 2D image on a plane like a
> >> monitor).  VTK will take the direction cosine and potentially flip the
> >> image along those cosines.
> >>
> >> Mark
> >>
> >> On Wed, Feb 23, 2011 at 9:38 AM, Jothy <jothybasu at gmail.com> wrote:
> >> > Hi all,
> >> >
> >> > I am trying to overlay an dose shade on a CT slice.I am using
> >> > vtkDICOMImageReader to read the CT and vtkGDCMImageReader to display
> the
> >> > dose shade.But I am having problem with the coordinates.How to relate
> >> > the
> >> > coordinates? For e.g: I  get ImagePositionPatient of CT image for
> >> > central
> >> > slice as [-275,-524,-128.25] and ImagePositionPatient for dose as
> >> > [-228.65,-419.25,-122.5] adn their spacings are [1.074,1.074,3] and
> >> > [2.52.5.2.5] respectively for CT and Rt dose.
> >> >
> >> > The image looks as in the attached figure.
> >> >
> >> > Any hint
> >> >
> >> > Thanks
> >> >
> >> > Jothy
> >> >
> >> >
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