title: [Basic concepts of radiology physics].
abstract: An x-ray tube mainly emits low-energy X-rays, with few maximum energy E₀ (equal in keV to the voltage U in kV) x-rays. Aluminium filtration (mandatory minimum thickness of 1.5 to 2.5 mm based on tube voltage) reduces soft X-rays and provides a mean energy equal to 2/3 E₀. The half value layer of a reference material characterizes the spectrum. X-ray attenuation in tissues is due to secondary electron interactions: photoelectric effect at low-energy, especially in dense materials with high Z number; compton effect at intermediate-energy, proportional to density. The optimization of acquisition parameters of a medically necessary examination is based on appropriate selection of the highest voltage (U in kV) providing the best contrast and lowest tube current (Q in mAs) providing a diagnostic image.
authors.affiliation: Service Central de Médecine du Travail, Hôtel Dieu, 1 place du Parvis Notre Dame, 75004 Paris, France.
authors.forename: D-J
authors.initials: DJ
authors.lastname: Gambini
mesh_terms: D000535:Aluminum; D004583:Electrons; D005374:Filtration / Q000379:methods; D006283:Health Physics / Q000379:methods*; D006801:Humans; D011829:Radiation Dosage; D011835:Radiation Protection / Q000379:methods*; D011871:Radiology / Q000379:methods*; D013679:Technology, Radiologic
chemical_list: D000535:Aluminum