As others already mentioned, you need to re-inteprolate the dose volume<span class="il"></span> <span class="il"></span>onto the CT data. To do that you must use the <span class="il">grid</span> <span class="il">frame</span> offset vectors.<br>
<br>For all dose images I've encountered, the spacing between these <span class="il">grid</span> 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):<br>
<br><i><font size="2"><span class="il">"Dose</span> Plane Spacing:<br>
If <span class="il">Grid</span> <span class="il">Frame</span> Offset Vector (3004,000C) is present, it must contain offset values yielding equally spaced <span class="il">dose</span> planes. Therefore, those values follow option a. in C.8.8.3.1 in Part 3 of [1]. RT <span class="il">Dose</span> Instances having unequally spaced <span class="il">dose</span> planes are not supported.</font></i>"<br>
<br>So for this specific case, where the grid plane spacing is the same, you could use the using the starting <span class="il">grid</span> <span class="il">frame</span> offset vector and the <span class="il">grid</span> 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.. <br>
<br>If you load the images in to 3DSlicer, I believe they should already be re-interpolated and placed in the right coordinate system.<br><br><br>--<br>karthik<br><br><br><br><br>
<div class="gmail_quote">On Thu, Feb 24, 2011 at 2:36 AM, Mark Roden <span dir="ltr"><<a href="mailto:mmroden@gmail.com">mmroden@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Hi Jothy,<br>
<br>
What are the direction cosines?<br>
<br>
There is a problem where VTK reinterprets the direction cosines to<br>
change the directions of images produced by the dicom reader.<br>
<br>
DICOM specifies that the image patient position is always the upper<br>
left pixel (if you look at the image as a 2D image on a plane like a<br>
monitor). VTK will take the direction cosine and potentially flip the<br>
image along those cosines.<br>
<br>
Mark<br>
<div><div></div><div class="h5"><br>
On Wed, Feb 23, 2011 at 9:38 AM, Jothy <<a href="mailto:jothybasu@gmail.com">jothybasu@gmail.com</a>> wrote:<br>
> Hi all,<br>
><br>
> I am trying to overlay an dose shade on a CT slice.I am using<br>
> vtkDICOMImageReader to read the CT and vtkGDCMImageReader to display the<br>
> dose shade.But I am having problem with the coordinates.How to relate the<br>
> coordinates? For e.g: I get ImagePositionPatient of CT image for central<br>
> slice as [-275,-524,-128.25] and ImagePositionPatient for dose as<br>
> [-228.65,-419.25,-122.5] adn their spacings are [1.074,1.074,3] and<br>
> [2.52.5.2.5] respectively for CT and Rt dose.<br>
><br>
> The image looks as in the attached figure.<br>
><br>
> Any hint<br>
><br>
> Thanks<br>
><br>
> Jothy<br>
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