title: [Principles and theoretical basis for photon and x-ray mineral determination].
abstract: The increasing spread of osteoporosis has made it necessary to develop improved diagnostic systems and to pay special attention to new techniques for the prediction of future risks. From a theoretical standpoint, it is known that by inserting between a radioactive source and a detector some higher density material, we obtain a decrease in the absorption counting rate. Through special mathematical models it is possible to determine the thickness of the absorbing material. This principle is at the basis of the first densitometer designed by Cameron and Sorenson. However such an absorption equation is valid only in case of constant density, while the human body is neither uniform nor linear. A first improvement is based on the use of radioactive sources characterized by two types of emission so as to be able to discriminate between various levels of tissue density. Improved densitometers include double photonic rays and use two variables mathematical models. The use of X rays instead of radioactive sources makes it possible to obtain clearer images, higher scanning speed, lower costs and total body examinations. Special attention is to be paid to machine calibration so to reach a perfect association between a well determined absorption counting rate and a well determined tissue thickness.
authors.forename: F
authors.initials: F
authors.lastname: Rudella
mesh_terms: D015502:Absorptiometry, Photon; D015519:Bone Density; D003198:Computer Simulation; D005260:Female; D005682:Gadolinium; D006801:Humans; D008297:Male; D008961:Models, Structural; D010024:Osteoporosis / Q000175:diagnosis*
chemical_list: D005682:Gadolinium
vernacular_title: Principi e basi teoriche della mineralometria a raggi fotonici ed a raggi X.