[vtkusers] Yet another VTK, DICOM and Orientation problem

Romain LEGUAY romain.leguay at gmail.com
Tue Dec 11 08:12:15 EST 2018

Hello everyone,

I'm trying to create a viewer of dicom with anatomical views (axial,
sagittal and coronal) from a radiologist point of view.

As starting point, I use the example provided in vtkDICOM module :
It uses vtkDICOMReader with SetMemoryRowOrderToFileNative activated.

When I try to display an axial CT scan, I don't obtain expected orientation
as you can see in pic1: the sagittal view is in Posterior -> Anterior
[image: pic1.png]

When I try to display a sagittal CT scan, I have different orientations:
[image: pic2.png]

To fix this orientation problem, I tried to create some transformation
matrices that converts
Patient Coordinates (DICOM) to World Coordinate (VTK coordinates).

To do this, I follow those steps:
* get the patient matrix (Pm) using the method
vtkDICOMReader::GetPatientMatrix (if I understand correctly, this matrix is
in DICOM space)
* create the rotation (Rm) from DICOM space to VTK space (rotation on VTK
X-axis around the origin point):
1 0 0 0
0 -1 0 0
0 0 -1 0
0 0 0 1
* Multiply Pm by Rm to obtain the matrix PRm to go from Patient Coordinates
to VTK Coordinates.
* Use the Matrix PRm with a point in IJK coordinates (voxel coordinates)
multiplied by the spacing.

I know I made a mistake because I don't have the result expected but I
don't know what I did wrong...

Can someone provide me some tips please?

Thank you,

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