Apparatus for radiation based imaging of a non-homogenous target area having distinguishable regions therein, the apparatus comprising: an imaging unit configured to: obtain four-dimensional radiation intensity data of at least two radioactive markers, from said target area in three spatial dimensions and a time dimension, where said at least two radioactive markers comprise: a first marker having a plurality of distinguishable region-dependent first marker radiation intensity time profiles; and a second marker having a plurality of distinguishable region-dependent, second marker radiation intensity time profiles, different from said first maker radiation intensity time profiles; detect radiation emitted by said at least two markers, where each said marker emits radiation at a different, distinguishable energy, and an image four-dimension analysis unit associated with said imaging unit for analyzing said obtained intensity data in said spatial and time dimensions configured, for each marker, to: identify, for said first marker, a first set of regions based on said plurality of distinguishable region-dependent, first maker radiation intensity time profiles; identify, for said second marker, a second set of regions based on said plurality of distinguishable region-dependent, second marker radiation intensity time profiles; and distinguish said distinguishable regions using said first set of regions and said second set of regions; output an image, based on said distinguishable regions. an imaging unit configured to: obtain four-dimensional radiation intensity data of at least two radioactive markers, from said target area in three spatial dimensions and a time dimension, where said at least two radioactive markers comprise: a first marker having a plurality of distinguishable region-dependent first marker radiation intensity time profiles; and a second marker having a plurality of distinguishable region-dependent, second marker radiation intensity time profiles, different from said first maker radiation intensity time profiles; detect radiation emitted by said at least two markers, where each said marker emits radiation at a different, distinguishable energy, and obtain four-dimensional radiation intensity data of at least two radioactive markers, from said target area in three spatial dimensions and a time dimension, where said at least two radioactive markers comprise: a first marker having a plurality of distinguishable region-dependent first marker radiation intensity time profiles; and a second marker having a plurality of distinguishable region-dependent, second marker radiation intensity time profiles, different from said first maker radiation intensity time profiles; a first marker having a plurality of distinguishable region-dependent first marker radiation intensity time profiles; and a second marker having a plurality of distinguishable region-dependent, second marker radiation intensity time profiles, different from said first maker radiation intensity time profiles; detect radiation emitted by said at least two markers, where each said marker emits radiation at a different, distinguishable energy, and an image four-dimension analysis unit associated with said imaging unit for analyzing said obtained intensity data in said spatial and time dimensions configured, for each marker, to: identify, for said first marker, a first set of regions based on said plurality of distinguishable region-dependent, first maker radiation intensity time profiles; identify, for said second marker, a second set of regions based on said plurality of distinguishable region-dependent, second marker radiation intensity time profiles; and distinguish said distinguishable regions using said first set of regions and said second set of regions; output an image, based on said distinguishable regions. identify, for said first marker, a first set of regions based on said plurality of distinguishable region-dependent, first maker radiation intensity time profiles; identify, for said second marker, a second set of regions based on said plurality of distinguishable region-dependent, second marker radiation intensity time profiles; and distinguish said distinguishable regions using said first set of regions and said second set of regions; output an image, based on said distinguishable regions.