Ch.7 Key Terms

Attenuation

Process by which beam of radiation is reduced in energy when passing through tissue or other materials

Automatic Rescaling

Process by which images are produced with uniform brightness and contrast, regardless of the amount of exposure

Brightness

Function of a display monitor; change image lightness/darkness

Contrast

Is the difference between the ranges of adjacent Image Receptor (IR) exposures represented as gray tones in an image

Contrast Resolution

Ability to distinguish between very subtle differences in image receptor exposures and differentiate them from the noise in the image

Data Drop

Condition due to extreme overexposure, which causes digital detector elements to become over-whelmed with photon energy and leads to drop of data during image reconstruction

Detector Element (DEL)

Pixel-size element of the digital radiography image receptor that has a fixed dimension in x- and y-orientation

Detector Saturation

Data drop that involves areas or regions of the digital detector

Digital Radiography (DR)

Digital image acquisition systems that convert x-ray energy into digital electronic signal for manipulation and display using direct or indirect conversion

Direct Conversion Flat-Panel Detector

Device that converts incident x-ray energy directly into an electronic signal, typically using a photoconductor as the x-ray absorber and a thin-film transistor as the signal collection area, which then sends the electronic signal to the computer for processing and viewing

Displayed Image Contrast

Relative brightness difference between the adjacent pixels in a digital image as viewed on a monitor

Distortion

Misrepresentation of the true size or shape of an object

Exposure Indicator

Numeric representation of the quantity of exposure received by a digital image receptor

Exposure Latitude

Range of exposures that produce a diagnostic-quality image

Fog

Undesirable exposure to the image receptor

Grayscale Bit Depth

Number of shades of gray that can be stored per detector element and displayed per pixel; ranges from 8 bits to 32 bits

Grid

Device consisting of thin lead strips designed to permit primary radiation to pass while absorbing scatter radiation

Half-Value Layer

Amount of filtration necessary to reduce the intensity of the radiation beam to one-half its original value

Image Receptor (IR)

Device used to capture the image for recording, such as photo-stimulable phosphor imaging plate or a digital flat-panel detector.

Image Receptor (IR) Exposure

Amount of ionizing radiation received by the image receptor

Indirect Conversion Flat-Panel Detector

Device that converts x-ray energy into light; the light is then detected by a charge-coupled device or photodiodes that are coupled with thin-film transistors, and converted into an electronic signal that is sent to the computer for processing and viewing

Inverse Square Law

Mathematic formula that describes the relationship between radiation intensity and distance from the source of the radiation

Kilovoltage Peak (kVp)

Measure of the potential difference, which controls the quality and affects the quantity of x-ray photons produced in the x-ray tube

Latent Image

Invisible image created after exposure but before processing

Raw Image Contrast

Contrast recorded in the image receptor prior to computer processing

Matrix

Series of picture elements (pixels) or detector elements arranged in rows and columns

Milliampere-Seconds (mAs)

Measurement of milliamperage multiplied by the exposure time in seconds, which controls the total quantity of x-ray photons produced in the x-ray tube

Penetrating Ability

X-ray beam passes through an object; controlled by the kilovoltage peak of the beam.

Penumbra

Fuzzy edge of an object as imaged radiographically; also known as image unsharpness

Photon

Quantum or particle of radiant energy

Pixel

Picture element and the smallest component of the matrix

Primary Radiation

X-ray beam after it leaves the x-ray tube and before it reaches the object or patient

Radiolucent

Permitting the passage of x-rays or other forms of radiant energy with little attenuation

Radiopaque

Not easily penetrable by x-rays or other forms of radiant energy

Remnant Radiation

Radiation resulting after the x-ray beam exits the object or patient

Scatter Radiation

Nondiagnostic Radiation produced from x-ray photon interactions with matter in such a way that resulting photons have continued in a different direction

Source-to-Image Receptor Distance (SID)

Distance between the source of the x-rays (usually the focal spot of the x-ray tube) and the image receptor

Spatial Resolution

Degree of accuracy of the structural lines actually recorded in the image

Subject Contrast

Range of differences in the intensity of the x-ray beam after it has been attenuated by the subject

Umbra

True edge of an object as imaged radiographically

Window Level

Digital image processing parameter that changes displayed image brightness on the monitor, usually through the use of a mouse

Window Width

Digital image processing parameter that changes displayed image contrast on the monitor, usually through the use of a mouse

Quantum mottle or quantum noise

Grainy image given to the lack of exposure

Two main categories of Image Quality factors

Image Signal and Image Resolution

Image Signal

Affects the visibility of the image

Image Resolution

Affects the sharpness and accuracy of the image

Two Image Signal Quality Factors

IR exposure and Contrast

Two Image Resolution Quality Factors

Spatial Resolution and Contrast Resolution

mAs Reciprocity Law

Any mA and time combinations producing equivalent mAs values that produce equivalent IR exposures(signal values).
mAs=to mAs.

mAs or Exposure Maintenance Formula

Conversion for compensation of distance of the Inverse Square Law