In film/screen radiography, optical density of resulting films, if used in conjunction with sensitometry-based quality control programs, provides a built-in, generic mechanism for maintaining stable technique factors and consistent image quality--improperly exposed films are recognizably non-diagnostic and thus (hopefully) repeated. Automatic exposure control (AEC) systems are even more important with CR and DR as a tool to avoid underexposed (noisy) or overexposed (excessive radiation) images and exposure creep. In lieu of optical density, digital systems often provide some form of post-read “exposure” or “speed” indication based on radiation reaching the receptor: the Fuji S-number, Agfa LGM number, etc. This lecture discusses the meaning of these speed indicators, how they may be used to evaluate proper AEC performance, and how they may be used maintain proper and stable manual technique factors to assure good image quality and acceptable patient dose.

Although previous lectures discussed many aspects of R&F performance evaluation, this lecture would “tie it all together” and overview a complete physics inspection of a (digital) radiographic or R/F system. Traditionally, physics tests tended to measure component-level parameters appropriate for comparison to specific component-level criteria: for example, indicated focal spot size, kVp accuracy and reproducibility, linearity, etc. This lecture should also include recommendations for system levels tests: i.e., designed to evaluate overall performance, such as limiting spatial resolution, image contrast, system speed and patient exposure under specific conditions, much like those performed as part of MQSA tests. It may include material associated with the ACR's Barium Enema accreditation program, as well as other recommendations elsewhere in this program.