The rendering on the left is the one based on ambient Occlusion. The right one is the default rendering. The scene graph is defined in the $OIVHOME/src/Medical/Rendering/Techniques/ambientOcclusion/medicalAmbientOcclusion.iv file. Set ambientOcclusion field from SoVolumeRenderingQuality to TRUE to activate ambient occlusion.
SoVolumeRender, SoVolumeRenderingQuality, SoVolumeData, SoTransferFunction