Using Amira I simplified two meshes and created a Level-of-Detail node in Inventor. Close up, the high resolution, high polygon count model is seen. When moved away, the low resolution, low polygon model is seen. Because the model is far away and takes up less screen real estate, the object should appear the same, because details are visible due to the reduction in size.
In practice this theory worked well for the brain model, but not the bunny model. For some unknown reason Amira decided to grossly decimate the bunny model instead of getting rid of some of the noise polygons in the background. This was disappointing. The solution is to get rid of the noise polygons (from the MRI data set) in the background, and this was attempted, but the attempt was unsuccessful, and I currently do not know how to remove them (easily).
Note: In order to view the level-of-detail model changes below, I have produced the animations without the model actually moving further away. I keep the model close so you can see it well, but this is only for the animations here. Using the actual Inventor node you would have to move the model away to see the change.