Apparatus for radiation based imaging of a non-homogenous target area having distinguishable regions therein, comprises: an imaging unit configured to obtain radiation intensity data from a target region in the spatial dimensions and at least one other dimension, and an image four-dimension analysis unit analyzes the intensity data in the spatial dimension and said at least one other dimension in order to map the distinguishable regions. The system typically detects rates of change over time in signals from radiopharmaceuticals and uses the rates of change to identify the tissues. In a preferred embodiment, two or more radiopharmaceuticals are used, the results of one being used as a constraint on the other.