DHA Radiology / Radiographer key terms

A radiation protection principle requiring that patient and staff doses be kept as low as reasonably achievable, weighing economic and practical factors while still obtaining the diagnostic information needed.

The maximum radiation dose a classified radiation worker may receive in a stated period, typically 20 mSv per year averaged over five years and 50 mSv in any single year.

A badge or device worn by a radiation worker that records cumulative radiation dose, usually by thermoluminescence or optically stimulated luminescence, and is read periodically to verify compliance with dose limits.

The three practical methods for reducing radiation exposure: minimising time near a source, increasing distance because dose falls with the square of distance, and inserting absorbing material.

The thickness of a given material that reduces the intensity of a radiation beam to half its original value, used to describe beam quality and to plan shielding.

Restricting the x-ray beam with adjustable shutters or cones so that only the region of clinical interest is irradiated, which lowers patient dose and reduces scattered radiation reaching the receptor.

A protective structure, such as a lead-lined wall or door, thick enough to attenuate the useful beam that may be aimed directly at it, unlike secondary barriers that stop only scatter and leakage.

A whole-body risk indicator, in sieverts, obtained by multiplying each organ's equivalent dose by a tissue weighting factor and summing the results so that different examinations can be compared.

The average absorbed dose in a tissue multiplied by a radiation weighting factor reflecting the biological harm of that radiation type; it is expressed in sieverts.

A radiation effect, such as cancer or heritable mutation, for which the probability of occurrence increases with dose while severity does not, and for which no threshold is assumed.

A tissue reaction such as skin erythema, epilation or cataract in which severity rises with dose and a practical threshold must be exceeded before the effect appears.

The principle that the intensity of radiation from a point source is inversely proportional to the square of the distance, so tripling the distance reduces intensity to one ninth.

The small area on the anode where electrons strike and x-rays are generated; a smaller focal spot sharpens detail, while a larger one tolerates greater tube current and heat.

X-rays produced when incident electrons are deflected and slowed by target nuclei, generating a continuous spectrum of photon energies whose maximum equals the kilovoltage peak.

The rule that receptor exposure depends on the product of tube current and exposure time, so different milliampere and time combinations giving the same mAs produce comparable image receptor exposure.

A device using chambers or detectors to measure radiation reaching the image receptor and terminate the exposure at a preset level, compensating for differences in patient thickness and attenuation.

An international standard that defines the format and communication protocols for medical images and associated data, enabling equipment from different manufacturers to store and exchange studies reliably.

Display controls that define the range of pixel values mapped to visible grey shades and the centre of that range, allowing structures of similar attenuation to be seen clearly.

The distance from the x-ray tube focal spot to the image receptor, which affects magnification, spatial resolution and the radiation intensity reaching the receptor.

The distance between the anatomical structure of interest and the image receptor; increasing it magnifies the structure and reduces the geometric sharpness of the recorded image.

The path of the central ray through the patient to the image receptor, named by the direction of entry and exit, for example anteroposterior or posteroanterior.

The height of the lead strips of an anti-scatter grid divided by the distance between them; a higher ratio removes more scatter but requires more precise alignment and higher dose.

A measure of how effectively an imaging system converts incident x-ray quanta into image signal while adding as little noise as possible, expressed as a percentage at a stated dose.

A measure of how well an imaging system transfers contrast at different spatial frequencies from object to image, indicating its ability to reproduce fine detail.

The ability of an imaging system to show two small structures close together as separate, often expressed as line pairs per millimetre or as the smallest discernible detail.

A number reported for a digital radiograph that indicates how much radiation reached the image receptor, used to judge technique adequacy rather than displayed image brightness.

A periodic review of radiographs that were repeated or discarded, classifying the reasons so that positioning, technique or equipment faults can be corrected and repeat dose reduced.

Scheduled tests and measurements of equipment performance, such as collimation accuracy, tube output and detector uniformity, compared with accepted limits to detect faults before they affect images.

A number on the computed tomography attenuation scale in which water is zero, air is about minus one thousand, and denser tissues have positive values.

A cross-sectional plane dividing the body into upper and lower portions, perpendicular to the long axis, which is the standard plane of computed tomography images.

Appearances on a radiograph: structures that absorb x-rays strongly appear white and are termed radiopaque, while those transmitting x-rays appear dark and are termed radiolucent.

Verifying identity using at least two independent details, such as full name and date of birth or file number, before any examination, procedure or administration of contrast.

Questioning patients of childbearing age about possible or known pregnancy before ionising examinations so that the procedure, shielding or timing can be adjusted to protect a fetus.

A water-soluble iodine-containing agent that attenuates x-rays and is given to outline blood vessels, organs or the urinary tract; concentration and osmolality affect tolerance and image quality.

Leakage of intravenously injected contrast medium from a vein into surrounding soft tissue, causing pain and swelling and occasionally skin injury; the injection must stop immediately.

A severe, immunoglobulin E-independent reaction to contrast medium with urticaria, bronchospasm or hypotension that can occur on first exposure and requires prompt emergency treatment.

Infection control measures applied to every patient regardless of diagnosis, including hand hygiene, gloves, gowns, eye protection and safe handling of sharps and body fluids.

Cleaning the hands with soap and water or an alcohol-based rub at specified moments, such as before and after patient contact, which is the single most effective way to prevent cross-infection.

A patient's voluntary agreement to an examination after receiving understandable information about its purpose, benefits, risks, alternatives and consequences, recorded before the procedure starts.

The legal and ethical duty to keep patient health information, including images and reports, private and to share it only with people involved in the patient's care or as authorised.