The shell collimation algorithm attenuates primary radiation which passes through the shell of a plaque. Secondary scatter effects are ignored. There are two algorithms available.

The circular lip algorithm is quite fast, but is appropriate only for plaques with thin, circular lips such as the standard COMS plaques. The complex lip algorithm employs a much slower ray-trace methodology but provides good results for plaques with arbitrarily shaped faces and perimeters.

When the Analyze plaque item is checked Plaque Simulator will automatically switch to the faster circular algorithm if the plaque has a nearly circular perimeter.