Glossary - General Radiography


Absorbed Dose

Energy transferred/deposited from ionizing radiation per unit mass of irradiated material; expressed in rad or gray.

Actual Focal Spot Size

Area on the anode target that is exposed to electrons from the tube current.

Air Kerma

A measure of the amount of radiation energy, in the unit of joules (J), actually deposited in or absorbed in a unit mass (kg) of air.  Therefore, the quantity, kerma, is expressed in the units of J/kg which is also the radiation unit, the gray (G).

Anatomic Programming Radiography (APR)

Technique by which graphics representing images of normal skeletal anatomy(human/animal) on the console guide the technologist in selection of a desired kVp and mAs by just selecting the particular body part(human/animal) to be examined.


Fluoroscopic process by which the X-Ray examination is guided toward visualization of blood vessels.


Fixed collimation of a diagnostic X-Ray tube, as in an aperture diaphragm.

Automatic Brightness Control (ABC)

Feature on a fluoroscopy system that allows the radiologist to select an image-brightness level that is subsequently maintained automatically by varying the kVp, mAs, or both.

Automatic Exposure Control (AEC)

Feature that determines radiation exposure during radiography in most X-Ray imaging systems.


Backscatter Radiation

X-Rays that have interacted with an object and are deflected backward.

Beam limiting device

Device that provides a means of restricting the size of an X-Ray field.


A Bucky is a device that moves the grid while the X-Ray is being taken. The motion keeps the lead strips from being seen on the X-Ray picture reducing noise giving clearer image for diagnosis.



Device used to restrict X-Ray beam size and shape.

Computed Radiography (CR)

Radiographic technique that uses a photostimulable phosphor (storage phosphor) as the image receptor. The resultant image can be digitized, stored and shared on computers.

Computed Tomography (CT)

Creation of a cross sectional tomographic section of the body by rotating an X-Ray fan beam and detector array  around the patient, and using computed reconstruction to process the image.


Degree of difference between the light and dark areas of a radiograph.

Contrast medium

Agent that enhances differences between anatomic structures.


Data Acquisition System (DAS)

Computer-controlled electronic amplifier and switching device to which the signal from each radiation detector of a multi-slice spiral computed tomographic scanning system is connected.

Detective quantum efficiency (DQE)

Describes how effectively an X-Ray imaging system can produce an image with a high signal-to-noise ratio (SNR) relative to an ideal detector.

Detector Array

Group of detectors and the interspace material to separate them; the image receptor in computed tomography.


Standard that enables imaging systems from different manufacturers to communicate.


Digital X-Ray imaging system that produces a series of dynamic images with the use of an area X-Ray beam and an image intensifier or flat panel detector.

Digital Radiography (DR)

Digital X-Ray imaging where digital X-ray sensors including flat panel detectors are used instead of traditional photographic film for static radiographs.

Dose Area Product (DAP)

Is a multiplication of the dose and the area exposed, often expressed in Gy.cm2. Modern X-Ray systems are fitted with a DAP meter, able to record accumulated DAP during an examination.


Instrument that detects and measures exposure to ionizing radiation.


Effective Focal Spot Size

Area projected onto the patient and image receptor.

Electron Volts (eV)

Is the amount of energy gained by the charge of a single electron moved across an electric potential difference of one volt.

Energy Subtraction

Technique that uses the two X-Ray beam energies alternately to provide a subtraction image that results from differences in photo electric interaction.


Measure of the ionization produced in air by X-Rays or gamma rays.  Quantity of radiation intensity expressed in Roentgen, Coulombs per kilogram or air kerma.


Falling load generator

Design in which exposure factors are adjusted automatically to the highest mA at the shortest exposure time allowed by the high voltage generator.

Fan beam

X-Ray beam pattern used in computed tomography projected as a slit.


Removal of low-energy X-Rays from the useful beam with aluminum or another metal.  It results in increased beam quality and reduce patient dose.


Imaging modality that provides a continuous image of the motion of internal structures while the X-Ray tube is energized.  Real time imaging.

Focal spot

Region of the anode target in which electrons interact to produce X-Rays.


Grid (antiscatter Grid)

Device used to reduce the intensity of scatter radiation in the remnant X-Ray beam.


Half Value Layer (HVL)

Thickness of the X-Ray absorber necessary to reduce the an X-Ray beam to half of its original intensity.

Hard X-Ray

X-Ray that has high penetrability and therefore is of high quality.



Image Intensifier

An electronic device used to produce a fluoroscopic image with a low-radiation exposure. A beam of X-Rays passing through the patient is converted into a pattern of electrons in a vacuum tube.

Inherent filtration

Filtration of useful X-Ray beams provided by the permanently installed components of an X-Ray tube housing assembly and the glass window of an X-Ray tube insert.

Inverse square law

Law that states that the intensity of radiation at a location is inversely proportional to the square of its distance from the source of radiation.

Ionization Chamber

The Ionization chamber is the simplest of all gas-filled radiation detectors, and is used for the detection or measurement of ionizing radiation.


Kilovolt peak (kVp)

Measurement of maximum electrical potential across an X-Ray tube; expressed in kilovolts.



Radiographic examination of the breast using low kilovoltage.

Milliampere (mA)

Measurement of X-Ray tube current.

Milliampere second (mAs)

Product of exposure time and X-Ray tube current.

Moving grid

Grid that moves during the X-Ray exposure.  Commonly found in a bucky.

Multi slice computed tomography

Imaging modality that used two detector arrays to produce two spiral slices at the same time.


Off focus radiation

X-Rays produced in the X-Ray tube anode but not at the focal spot.

Object to image receptor distance (OID)

Distance from the image receptor to the object that is to be imaged.


Photoelectric effect

The emission of electrons from a material, such as a metal, as a result of being struck by photons.

Photomultiplier Tube (PMT)

An electron tube that converts visible light into an electrical signal.


Electromagnetic radiation that has neither mass nor electric charge but interacts with matter as though it is a particle; X-Rays and gamma rays.



An X-Ray photon.


Radiation Absorbed Dose (Rad)

Special unit for absorbed dose and air kerma.  1 rad = 100 erg/g = 0.01 Gy.

Radiation quality

Relative penetrability of an X-Ray beam determined by its average energy; usually measured by half-value layer or kilovolt peak.

Radiographic technique

Combination of setting selected on the control panel of the X-Ray imaging system to produce a quality image on the radiograph.


Imaging modality that uses X-Ray film and/or detector and usually an X-Ray tube to provide fixed (static) images.


Scatter Radiation

X-Rays scattered back in the direction of the incident X-Ray beam.

Soft X-Ray

X-Rays that has low penetrability and therefore low quality.

Source to image receptor distance (SID)

Distance from the X-Ray tube to the image receptor.

Spatial resolution

Ability to image small objects that have high subject contrast.

Starter (tube starter)

Rotating anode X-Ray tubes utilize an induction motor to rotate the anode assembly.  A starter or motor controller is used to apply power to the X-Ray tube motor for rotation.



A sectional image is made through a body by moving an X-Ray source and the film in opposite directions during the exposure. Structures in the focal plane appear sharper, while structures in other planes appear blurred.

Total Filtration

Inherent filtration of the X-Ray tube plus added filtration.



Penetrating, ionizing electromagnetic radiation that has a wavelength much shorter than that of visible light.