vtk memory and time consumption

[fmri]

Dear list members,

to visualize 3D CT or MRI data of the skull I am using variants of

vtkVolume16Reader->vtkMarchingCubes->vtkDecimatePro->vtkStripper->vtkPolyDataMapper->vtkLODActor

or

vtkVolume16Reader->vtkVolumeRayCastMapper->vtkVolume->vtkRenderer

In either case memory requirements are tremendous. In the case of ~100MB
CT data all memory and swap space are eaten up bringing a RedHat 6.1
Linux box to complete standstill.
In case of a moderately sized MRI volume (~25 MB) it takes 3-5 minutes
to render the polygon mesh or up to 10 minutes to bring the ray casted
volume to screen (500MHz PIII, Matrox GS400, 16MB).
A costum written raycaster manages to render the MRI scenes in less than
20sec, the CT derived bone even faster.

Is there a way to improve the memory consumption and speed (while
keeping the current hardware) ?
How can I find out which parts of the pipeline consume the memory ?
In the meshing case I'd like to dispose of the source object
vtkVolume16Reader after performing the isosurface extraction to return
its memory - how can this be done best ?
Which recipe was the ray casting algorithm derived from ?

Above I used unsegmented data, but actually I should prefer using a
labelled atlas volume (which in my case would be half the size of the
greylevel volume) and resort to the surface normals of the grey level
volume only for the ray casting. Can somebody please give me a clue to a
reasonable way to do this in vtk ?

Thanks a lot !

Arno R. Schleich, MS, MD
Dpt. of Otorhinolaryngology
Freie Universitaet Berlin


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