View article

Progress in nuclear physics acquired during World War II has naturally led many scientists to devote their research activities to the field of tomographic imaging techniques using ionizing radiation. This was, in the post-war booming economy, particularly of great importance for medical diagnostic as well as for industrial non destructive evaluation (NDE). As the objective is to extract information on the inner part of objects of interest, penetrating radiation was the most appropriate agent for this purpose. With the availability of high quality X-ray and gamma-ray sources (either directly originated from nuclear transitions or from pair annihilation) and the emergence of sensitive detectors, three types of imaging have been introduced and developed throughout half a century. Nowadays they have emerged as mature standard investigation methods for several domains of application.

These are: a) the X-ray transmission Computed Tomography (CT), which exploits the physical law of radiation attenuation in matter, b) the Single Photon Emission Tomography (SPECT), which uses the possibility of implanting radiation sources inside objects, c) the Positron Emission Tomography (PET), which uses the possibility of implanting positron sources in objects and exploits the properties of electron-positron pair annihilation. Milestones of their sensational evolution throughout decades are vividly recalled in recent reviews, see eg [35, 47].