1. A system comprising: a display unit; one or more processors configured to display an image and associated information on the display unit, wherein the image comprises an external representation of at least a portion of an object superimposed with a light representation, the light representation corresponding to the location and magnitude of electro-magnetic radiation emitted from an internal portion of the object; and a graphical user interface running on one or more of the processors and providing the image on the display, wherein the graphical user interface further comprises a first selectable tool for defining a region of interest on the image and a second selectable tool for performing a measurement on the defined region of interest; and wherein the one or more processors are configured so that when a user activates the second tool, the one or more processors calculate information about a portion of the image within the defined region of interest.