Visualizing medical data involves combining various data sets into a single scene, and exploring the scene interactively. Using Slicer typically involves creating a scene from volume data sets, surface models derived from those volumes, and transformations derived from 3D registrations of both the volumes and models. We have found that the proper coordination of these items is easier to attain by using a hierarchical modeling paradigm, similar to the modeling systems and languages of graphics and CAD/CAM.

Toward this end, we created the Medical Reality Modeling Language (MRML) as a format for describing scenes that consist of various types of data sets collected in various geometric locations. These scenes can then be explored using programs that are essentially MRML browsers, such as Slicer.

MRML files describe three aspects of data:

• Disk Location: MRML files are not a copy of the data in another format. Instead, a MRML file describes where the data is stored, so that the data can remain in its original format and location.

 
• Geometric Position: A MRML file describes how to position the data sets relative to each other in 3D space.

 
• Appearance: A MRML file describes how to display the data, by specifying parameters for rendering and coloring.