[vtkusers] Fwd: how to position/orient a DICOM volume

[Elvis Chen]

hi all,

I should mention that I'm writing my own volume viewer in straight
OpenGL so that multiple (and overlapping) volume can be rendered
correctly.  This is why I need to know how to position/orient the
dicom volume (outside of the vtk framework).  I'm using
vtkDICOMImageReader and vtkImageExport to read dicom volumes and
access them within OpenGL context.

Any help is very much appreciated,

Elvis

---------- Forwarded message ----------
From: Elvis Chen <elvis.chen at gmail.com>
Date: Oct 12, 2007 5:04 PM
Subject: how to position/orient a DICOM volume
To: vtkusers at vtk.org


hi all,

I would like to display multiple DICOM volumes in a common coordinate
system (MRI machine, for example) so that volumes of different
anatomies are displayed in their correct poses (relative to each
other).  Using DataExtent and DataSpacing, one can compute the *real*
size of the volume, but I'm not clear on how to position and orient a
DICOM volume.

>From the documentation the following two functions seems to give the
absolute geometry of a DICOM volume (from vtkDICOMImageReader):

GetImageOrientationPatient()
Get the (DICOM) directions cosines. It consist of the components of
the first two vectors. The third vector needs to be computed to form
an orthonormal basis.

GetImagePositionPatient()
Get the (DICOM) x,y,z coordinates of the first pixel in the image
(upper left hand corner) of the last image processed by the
DICOMParser

However, the descriptions are not informative enough for me to render
the DICOM volumes correctly.  Can someone please explain if I'm on the
right track, or is there another to get the absolute geometry of a
DICOM volume?

any help is very much appreciated,

Elvis