1. A device for presenting a halftone pictorial representation of radioactivity distribution within a specimen, said device comprising: a. means for detecting a number of radioactive events at X, Y locations within the specimen; b. computer means operatively connected to said detecting means for generating coded signals proportional to the number of radioactive events detected at each X, Y location; c. display means for presenting a pictorial representation comprised of a plurality of like profile picture elements, each said picture element defining a matrix having a plurality of like profile sections; and d. conversion means operatively connected to said computer means and display means, said coded signal selectively applied to said display means via said conversion means, said conversion means generating character code signals in response to said coded signals, said character code signals representing a specified number of dot elements per unit area for each said picture element, the number of dot elements per unit area in each said picture element defining a shade in the Gray scale, said dot elements and said sections having like profiles, said pictorial representation presented by said display means being a halftone presentation of radioactivity distribution within the specimen.