Introduction: PET is a technique for measuring the concentrations of positron-emitting radioisotopes within the body by registering the emitted annihilation radiation. At present, the basic process employed in PET is the annihilation of the emitted positron an electron that results in two almost co-linear gamma-photons travelling in opposite directions, each with 511 keV energy. In the conventional PET decay events are just localized in space and counted, but no other characteristics of the annihilation radiation is explored. Recently it has been shown, that extra information could also be obtained in PET by registering the annihilations into three photons. In spite of the relative rareness of positron annihilation into three photons, it may still be exploited to develop a new imaging modality. Although the rate of 3gamma decays is small, the positioning information conveyed by a single event is much larger than in the case of two gamma, so the total information gained from three gamma may be significant.Methods: Three high resolution detectors arranged in a plane forming angels of about 120o with respect to each other to form a primitive 3-gamma scanner. Each detector generates pulse, which passes to a time pickoff units. Timing signals from the pick-off units are passed to a coincidence unit with timing window of t. If pulses overlap, then logic signal is generated and passed as a trigger to simultaneous sampling analogue-todigital converter (ADC).Results and Conclusion: Three gamma imaging would provide information not only about the local concentration of radionuclide, but also, by virtue of chemical interactions of Positronium, the local chemical environment in tissue. In particular, the concentration of free oxygen could be determined, which would be a significant advantage in oncological applications of PET.