The geometry may be captured by a variety of imaging modalities, or it may be analytically defined for very regular structures or symmetric cells. Internal structures that are included in the physiological model, but are not spatially resolved, may be mapped continuously as a volume fraction of the enclosing compartment. Segmentation is necessary to define discrete regions that represent the anatomical features of interest. Membranes are implicitly represented as the boundary between dissimilar compartments. A compartmental model represents a single point simulation based on the defined physiological model, the surface to volume ratio and volume fractions.
Compartmental models are useful in calculating quick approximate solutions.
The regions defined in the geometry model are mapped to structures defined in the physiology model. Compartmental models represent a single point simulation. Multiple regions within such a model are still mapped to a single compartment. Simulation context allows for the specification of spatially accurate initial conditions and boundary conditions for each species of each structure. This results in a set of nonlinear ordinary differential equations that typically are solved in seconds.