Method for forming a gamma image by combining a compton imaging modality and a coded mask imaging modality

A method of estimating positions of irradiating sources in a field of observation, using a gamma camera, the gamma camera comprising:

• a detection material;
• pixels distributed over a detection surface of the detection material, each pixel being configured to form a detection signal associated with the detection of an interaction of an ionizing photon in the detection material;
• a collimator, facing the detection material, and defining a first field of observation, included in the field of observation of the gamma camera;
• a location unit, configured to assign a position to each interaction in the detection material, using the detection signal generated by said interaction;
• a spectrometry unit, configured to assign an energy to each interaction detected, on the basis of the detection signal associated with said interaction;
• a coincidence unit, configured to identify each interaction as a single or multiple interaction, a multiple interaction being formed from two scattering interactions detected in temporal coincidence;
• a memory, configured to store detected interaction parameters;
• the method comprising:
• a) acquiring detection signals by the pixels within an acquisition period, each detection signal being associated with a detected interaction;
• b) on the basis of the detection signals, assigning a position and an energy to each interaction detected;
• c) identifying each detected interaction as a single or multiple interaction;
• d) using the memory to store the parameters of each interaction, whether single or multiple, the parameters of each interaction comprising the position and energy of said interaction;
• wherein the method further comprises:
• e) selecting an isotope from a list of isotopes;
• f) according to the energy assigned to each interaction, whether single or multiple, calculating a probability of emission by the isotope;
• g) on the basis of the parameters of each interaction, whether single or multiple, calculating a probability of emission of the photon that has generated the interaction, from different points in the field of observation;
• h) calculating an a priori probability of emission of a photon for the selected isotope, from the different points of the field of observation;
• i) according to the probabilities resulting from g) and h), calculating a spatial distribution of emission intensity in the first field of observation for the isotope selected in step e).