opacity based rendering


Most people usually think of colour as a composite of Red, Green, and Blue; or Cyan, Magenta, Yellow.  Computer graphics cards that deal with tridimensional rendering also use a fourth component - Alpha, or opacity.  By mapping or converting the luminance of an image to an Alpha value, this opacity component can be used to reconstruct a virtual radiograph from CT data and viewed from any angle with or without stereo aids and the viewer can alter the viewpoint or opacity of the image in real time.

Display of reconstructed CT or MRI data has been done as a surface structure with lighting algorithms applied.  This has mainly been due to the fact that using a surface model decreases the amount of data that needs to be processed.  It does have drawbacks: One cannot "see-into" the volume, the surface generation algorithms smooth over regions than one may want to see, and the lighting algorithms also come at increased computational cost.  With the advances in computer technology, viewing the full volumetric data set can be done on a modest computer platform with a reasonable graphics card at home or on the move - this reduces the surgeon's dependency on the radiology department and their expensive Silicon Graphics workstations.

I have not uploaded any full volumes here, as it is all real patient data and will not be made freely available.  If you are interested and want some examples, email me with your professional details.

Opacity rendering tutorials

The two programs that I use are VolView from Kitware and AMIDE, an opensource development by Andy Loening.

Kitware has very kindly built in DICOM file support to VolView which makes it easy to open a 3D DICOM file or convert a stack of DICOM images into a single 3D file.

AMIDE is a useful program that allows volume rendering in parallel view stereo with alteration of the stereo parameters, as well as tools to remove extras such as plaster casts or CT tables.

To use either of the programs to look at CT data like a "virtual radiograph" follow the links below:

VolView tutorial

AMIDE tutorial