Principles and precautions of conventional radiography

The production of X-rays and the different techniques available to image them are described. The types and applications of contrast agents are discussed, along with side-effects and how to avoid/minimize them. Standard radiographic projections are detailed and the methods used to improve image quality mentioned. The radiation dose for a number of radiographic procedures is listed, along with regulations governing their administration; methods of reducing the radiation dose are discussed. X-rays are high-energy electromagnetic photons produced by bombarding an anode with electrons. X-rays are used in diagnostic imaging, in conventional radiography and CT. Tissues absorb X-rays according to their density. Conventional radiographs allow the resolution of four densities (air, fat, soft tissue, calcification). Imaging can also be performed fluoroscopically or digitally. If there is no natural contrast, exogeneous contrast agents may be used to artificially enhance visualization of tissue and have a wide spectrum of applications. Contrast agents may be classified as 'positive' (e.g. barium) or 'negative' (e.g. air) according to whether they are of high or low radiodensity. X-ray exposure should be performed only when it produces a net benefit to the patient and should be kept as low as reasonably achievable (the ALARA principle). The UK Ionising Radiation (Medical Exposure) Regulations require by law that all medical exposure to ionizing radiation is clinically justified and authorized.