A computer-implemented method for obtaining a light distribution located inside an animal, the method comprising: obtaining multiple fluorescence images of at least a portion of the animal; obtaining a three dimensional representation of a surface portion of the animal; dividing the representation of the surface portion into a set of surface elements; mapping fluorescence image data from a subset of the multiple fluorescence images to surface elements to create fluorescent light emission data from the surface portion of the animal (206, 306), converting fluorescence light emission data for each one of the surface elements into a photon density just inside the surface; determining a first three-dimensional representation of a fluorescent probe distribution internal to the animal using the photon density, wherein said determining includes: modeling autofluorescence and separating the contributions of tissue autofluorescence from the fluorescent light emission data (208, 308), dividing the interior volume of the animal into volume elements; modelling internal light propagation from a position of an excitation illumination source to the surface elements (314, 316); determining the three-dimensional representation of a fluorescent probe distribution using the modelled internal light propagation and the photon density and characterised by determining, in an iterative solution process, multiple additional three-dimensional representations of a fluorescence probe by varying the subset of fluorescence images; comparing the determined three-dimensional representations; and selecting one of the determined three-dimensional representations on the basis of the comparison. obtaining multiple fluorescence images of at least a portion of the animal; obtaining a three dimensional representation of a surface portion of the animal; dividing the representation of the surface portion into a set of surface elements; mapping fluorescence image data from a subset of the multiple fluorescence images to surface elements to create fluorescent light emission data from the surface portion of the animal (206, 306), converting fluorescence light emission data for each one of the surface elements into a photon density just inside the surface; determining a first three-dimensional representation of a fluorescent probe distribution internal to the animal using the photon density, modeling autofluorescence and separating the contributions of tissue autofluorescence from the fluorescent light emission data (208, 308), dividing the interior volume of the animal into volume elements; modelling internal light propagation from a position of an excitation illumination source to the surface elements (314, 316); determining the three-dimensional representation of a fluorescent probe distribution using the modelled internal light propagation and the photon density and characterised by determining, in an iterative solution process, multiple additional three-dimensional representations of a fluorescence probe by varying the subset of fluorescence images; comparing the determined three-dimensional representations; and selecting one of the determined three-dimensional representations on the basis of the comparison.