PRC RadTech key terms

The vacuum tube inside a protective housing where X-rays are produced: electrons boiled off a heated filament at the cathode are accelerated by high voltage and strike a metal target at the anode.

The release of electrons from a heated filament, usually tungsten, when current passes through it. In the X-ray tube this electron cloud at the cathode is the source of tube current.

German for braking radiation. It is produced when a fast electron is slowed or deflected by the electric field of a target nucleus, emitting X-ray photons of many energies and forming the continuous spectrum.

X-rays produced when an incoming electron ejects an inner-shell electron of a target atom and an outer-shell electron falls into the vacancy, releasing a photon with an energy fixed by that atom's binding energies.

Tube current in milliamperes multiplied by exposure time in seconds. It reflects the total number of electrons crossing the tube and therefore the number of X-ray photons produced, controlling receptor exposure.

The highest voltage applied across the X-ray tube during an exposure, in kilovolts. It determines electron energy and therefore beam penetrability, patient dose, and image contrast.

The intensity of radiation from a point source is inversely proportional to the square of the distance from that source. Doubling the distance reduces intensity to one quarter of its original value.

The thickness of a stated material, usually aluminum, that reduces the intensity of an X-ray beam to half its original value. It is a standard measure of beam quality and filtration.

A photon gives all its energy to an inner-shell electron, which is ejected; the vacancy is then filled with emission of characteristic radiation. It occurs mostly with low-energy photons and high-atomic-number tissues such as bone.

A photon transfers part of its energy to an outer-shell electron, which is ejected, and the photon continues in a new direction with lower energy. This produces scatter radiation and reduces image contrast.

A device with adjustable lead shutters mounted at the tube port that shapes the beam to the area of interest. It reduces patient dose and scatter and improves image contrast.

A plate of closely spaced lead strips separated by radiolucent spacers, placed between the patient and the receptor. It absorbs scatter before it reaches the receptor, raising contrast at the cost of higher dose.

A sheet of phosphor material in a cassette that converts X-ray photons into light, which then exposes film or a detector. The light exposes the receptor far more efficiently than X-rays alone, allowing lower exposure factors.

The reusable imaging plate used in computed radiography. X-ray energy is stored in a phosphor layer and later released as light when the plate is scanned by a laser, forming a digital image.

A solid-state digital receptor, commonly using amorphous silicon or selenium, that converts X-rays directly or indirectly into electrical charge held in a pixel matrix and read out as a digital image.

Picture Archiving and Communication System: a network of computers and storage devices that holds, transmits, and displays digital medical images so they can be viewed across a facility and beyond.

Digital Imaging and Communications in Medicine, the international standard defining how medical images and related information are formatted, stored, and exchanged between imaging equipment and information systems.

The central portion of the X-ray beam, travelling along the long axis of the tube and directed at the part being examined. Correct alignment of this ray limits distortion of the image.

The distance from the X-ray tube focal spot to the image receptor. It affects magnification, recorded detail, and the radiation intensity reaching the receptor.

The distance between the body part being imaged and the image receptor. Increasing it increases magnification and reduces recorded detail, so it is kept as small as is practical.

The standard reference posture: standing upright, facing forward, arms at the sides with palms forward, and feet together. Positioning terms such as anterior and proximal are defined relative to it.

A supine position in which the head is lowered and the feet raised, so the head lies below the hips. It is used for certain abdominal and contrast studies and for some patients in shock.

A position in which the patient lies down, commonly on one side, with a horizontal X-ray beam used to show air-fluid levels or free air. It is named for the side the patient lies on.

The ability of an imaging system to record small, closely spaced objects as separate structures. It improves with smaller pixels and focal spots and shorter object-to-image distance, and is measured in line pairs per millimeter.

The ability of an imaging system to distinguish tissues that differ only slightly in density or signal. Digital receptors have a much wider contrast resolution than film, so subtle differences can be displayed.

A grainy, mottled appearance caused by too few X-ray photons reaching the receptor, so statistical variation between pixels becomes visible. Increasing mAs or kVp reduces it.

A numeric value shown by a digital imaging system that indicates how much radiation reached the receptor. It is used to judge whether technique was adequate and is not itself a measure of image quality.

A graph of how many pixels in a digital image carry each signal value. Image processing uses it to locate the useful range of values and to set appropriate brightness and contrast.

Adjusting the displayed brightness (window level) and contrast (window width) of a digital image without altering the stored data, so different tissues can be assessed from a single exposure.

Misrepresentation of the size or shape of an object in the image. It results from magnification, unequal magnification of different parts, or misalignment of the part, receptor, and beam.

As Low As Reasonably Achievable: the principle that every radiation exposure should be kept as low as can reasonably be achieved, taking economic and social factors into account, using time, distance, and shielding.

A badge or ring worn by radiation workers, such as a thermoluminescent dosimeter or optically stimulated luminescence badge, that records the radiation dose received during a monitoring period.

Lead shielding placed over the reproductive organs of patients who are young or of childbearing age during examinations where the gonads lie in or near the beam, to reduce genetic dose.

A quantity in sieverts that expresses the overall risk from a partial or whole-body exposure by weighting the dose to each tissue for its radiation sensitivity, allowing different procedures to be compared.

The Radiologic Technology Act of 1992, the Philippine law that regulates the practice of radiologic technology, including licensure, scope of practice, and the board that administers the profession.

A patient's voluntary agreement to a procedure after being told its purpose, what will happen, the risks and benefits, and the alternatives, given by a patient able to decide.

The duty to keep a patient's personal and medical information private and to share it only with those who need it for care or as the law allows.

The legally defined set of duties and procedures that a licensed radiologic technologist is permitted to perform, established by law and by the profession's rules and regulations.

Failure to provide the standard of care that a reasonably competent radiologic technologist would provide in the same circumstances, resulting in harm to a patient.