Glossary

Actual focal spot	Area on the anode/target that is exposed to electrons emitted from the filament.
Anode	Postive side of the x-ray tube. Often used synonymously with the word target.
Anode angle	Angle (in degrees) between the target surface and a verticle line drawn from down from the center of the anode.
Artifact	A misrepresentation of structures or anatomy
Automatic Exposure Control	Device that terminates the x-ray exposure when a pre-determined target dose to the detector has been achieved. Also called the Phototimer
Bit depth	Determines the number of gray levels each pixel can display. A 10 bit system can display 210 =1024 shades of gray.
Blur	Spreading of the x-ray signal which results in decreased spatial resolution.
Bremmstreahlung x-ray	X-ray emitted when a charged particle (electron) interacts with the positively charged nucleus causing the electron to de-accelerate. Also called Radiative emission.
Bucky Factor	Ratio equal to the patient dose with a grid to the patient dose without a grid.
Cathode	Negative side of the x-ray tube that contains the filament and the focusing cup.
Characteristic x-ray	X-ray emitted when electrons transition from outer orbital shells to inner orbital shells. Characteristic x-ray energy is equal to the difference in shell binding energies.
Classical Scatter	X-ray photon interacts with the entire atom and results in scattering of the x-ray with no transfer of photone energy to patient tissues.
Coherent Scatter	See Classical Scatter
Collimation	Changing of the x-ray beam size through adjustment of the lead collimator blades.
Compton Scatter	Occurs when an x-ray photon transfers some of it’s energy to an outer shell electron which is ejected. The photon direction is changed, and it’s energy is reduced.
Contrast	The difference in gray scale between two adjacent areas in an image.
Direct DR	Type of digital detector that converts x-ray signal directly to charge.
Dynamic Range	The change in grayscale value displayed per unit change in dose to the imaging receptor.
Effective focal spot	The size of the x-ray beam path projected off the actual focal spot onto the image receptor.
Excitation	Charged particle interaction that produces heat.
Exposure time	Duration of x-ray beam emisssion from the target.
Field-of-view	Size of the x-ray beam projected onto the image receptor
Filament	Thin coil of wire through which a large current is passed, which heats the filament and boils off electrons. Part of the cathode.
Filtration	Thin pieces of metal placed between the x-ray tube and the collimator to absorb very low x-rays emitted from the target before they reach the patient.
Grid	Device located just above the image receptor to absorb scattered x-rays and improve image contrast.
Grid cutoff	Absorption of un-scattered, primary x-rays in the grid.
Grid ratio	Ratio equal to the height of the lead septa in the grid to the width of the interspace material between the lead septa.
Half-value layer	Thickness of material (typically given in aluminum) required to reduced the intensity of the beam to 50% of it’s original intensity. Measure of x-ray beam quality.
Heel effect	A decrease intensity of the x-ray beam on the anode side of the image receptor due to increased attenuation in the anode.
In-direct DR	Digital image receptor that contains a phosphor material that converts x-ray energy to visible light which is subsequently converted to charge.
Ionization	The removal of an orbital electron from the atom.
Kerma	Kinetic energy released in matter. Unit is the J/kg or Gray (Gy).
kV	unit of electrical potential difference applied between the cathode and the anode
Low contrast resolution / visibility	Ability to resolve objects that have very little difference in grayscale value from surrounding structures.
mA	Unit of electrical current.
mAs	The product of tube current (mA) and exposure time (s). Determines the total number of electrons that impact the anode target.
Matrix	The number of rows or columns of pixels in and image. In digital image receptors, the matrix size is equal to the number of rows and columns of detector elements.
Noise	Random variation in signal to the image receptor.
OID	Object-to-image distance.
Phosphor	A material that converts energy into visible light.
Photocell	An individual radiaton detector that is part of the automatic exposure control system.
Photoelectric Effect	Total absorption of an xray photon followed by the ejection of an orbial electron.
Phototimer	See Automatic Exposure Control
Pixel	A digtal picture element.
Quality	Describes the penetrating ability (energy) of the emitted x-ray beam.
Quantity	Describes the number of x-ray photons emitted in the x-ray beam.
Quantum Noise	Random distribution of x-ray signal onto the image receptor elements. Inversely related to the incident number (quanta) of x-ray photons reaching the receptor .
Scintillator	A material that converts energy into visible light.
SID	Source-to-image receptor distance. Distance of the x-ray tube target to the image receptor.
SOD	Source-to-object being imaged distance.
Spatial resolution	Ability to resolve two high contrast objects as they become smaller or closer together.
SSD	Source-to-skin distance. Distance of the x-ray tube target to the patient’s skin
TFT	Thin-film transistor. Controls the readout of signal from direct and indirect digital radiographic detectors.
Tube current	Rate at which electrons flow from the cathode to the anode in an x-ray tube.
Tube voltage	Electrical potential difference applied between the cathode and the anode.