1. A GAMMA/RF compact, hybrid and integrated system for PET-SPECT/MR simultaneous imaging, having a GAMMA/RF device comprising: an RF coil comprising spaces that allow a passage of at least a significant part of a GAMMA radiation generated internally; and a set of GAMMA radiation detector modules arranged radially around the RF coil, wherein each GAMMA radiation detector module comprises: a scintillator crystal configured to emit light when it receives GAMMA emission, a focusing system comprising: a first face coupled to the scintillator crystal configured to receive the light, and a second face comprising: lenses configured to focus the light received from the scintillator crystal to photodetectors of an array of photodetectors, wherein a configuration of the lens is such that the total width of the focused light coincides with each photodetector, and spaces between lenses which are dead zones of the focusing system, an RF shielding layer, placed between the focusing system and the array of the photodetectors, comprising circular holes aligned with the respective lenses, wherein each of the circular holes is configured to allow the focused light from respective ones of the lenses to pass through to the respective photodetectors, wherein the RF shielding layer provides shielding in the dead zones of the focusing system, the array of the photodetectors placed behind the RF shielding layer so as to receive the light, faced to the second face of the focusing system, and a processor configured to process signals generated by the photodetectors.