ABSTRACT
This chapter focuses on the several applications and discusses some definitions concerning interactions of radiation with matter, with special regard to imaging methods used in medical physics. It presents a summary of the most important points for readers new in the field, and a selection of the most important equations. As early as the eighteenth century it was shown by macroscopic observations that the attenuation of visible light relates to the properties of the material through which the light is travelling. Similar to visible light, W. K. Rontgen observed that the attenuation of X-rays in matter as measured as exposure on a photographic film followed the J. H. Lambert–A. Beer law. In the particle picture of X-rays, the aforementioned mean intensities should equalize mean numbers of photons, together with the associated variances. In the range used for clinical radiography, the scattered X-rays are emitted predominantly in the lateral direction, and change insignificantly as the incident photon energy is increased.
