Ch. 9 Image Quality and Characteristics Flashcards
any unwanted image on a radiographic image
artifact
number of bits that determines the amount of precision in digitizing the analog signal, and therefore the number of shades of gray that can be displayed in the image
bit depth
the amount of luminance (light emission) of a display monitor
brightness
differences in the brightness levels to differentiate among the anatomic tissues
contrast
used to describe the ability of the imaging system to distinguish between small objects that attenuate the x-ray beam similarly in digital imaging
contrast resolution
a method of describing the contrast resolution compared with the amount of noise apparent in a digital image
contrast-to-noise ratio
a measurement of the efficiency of an image receptor in converting the x-ray exposure it receives to a quality radiographic image
detective quantum efficiency (DQE)
results from the radiographic misrepresentation of either the size (magnification) or shape of the anatomic part
distortion
the range of exposure intensities that an image receptor can respond to and acquire image data
dynamic range
refers to image of objects that appear longer than the true objects
elongation
provides a numeric value indicating the level of radiation exposure to the digital image receptor
exposure indicator
the dimensions of an anatomic area displayed on the monitor
field of view
refers to images that appear shorter than the true objects
foreshortening
the number of different shades of gray that can be stored and displayed by a computer system in digital imaging
grayscale
tissues that attenuate the x-ray beam very differently
high subject contrast
tissues that attenuate the x-ray beam similarly
low subject contrast
an increase in the image size of an object compared with its true, or actual, sizes; also known as size distortion
magnification
combination of rows and columns (array) of pixels that make up a digital image
matrix
a measure of the ability of the system to reserve signal contrast (display the contrast of anatomic objects varying in size), and the value will be between 0 (no difference in brightness levels) and 1.0 (maximum difference in brightness levels)
modulation transfer function (MTF)
also called number of bits, it affects the number of shades of gray available for image display
pixel bit depth
number of pixels per unit area
pixel density
the pixel spacing or distance measured from the center of a pixel to an adjacent pixel
pixel pitch
visible as brightness fluctuations on the image. Caused by too few photons reaching the image receptor to form the image
quantum noise
the ability of the imaging system to resolve or distinguish between two adjacent structures and can be expressed in the unit of line pairs er millimeter (lp/mm)
resolution
when the image receptor is extremely overexposed, cannot be properly processed, and the quality is severely degraded
saturation
the accuracy of the structural line is achieved by maximizing the amount of spatial resolution and minimizing the amount of distortion
sharpness factors
a method of describing the strength of the radiation exposure compared with the amount of noise apparent in a digital image
signal-to-noise ratio
refers to an increase in the object’s image size compared with its true, or actual, size; also known as magnification
size distortion
a term used to evaluate accuracy of the anatomic structural lines
spatial resolution
refers to the absorption characteristics of the anatomic tissue radiographed along with the quality of the x-ray beam
subject contrast
factors that make the anatomic structures visible and include the brightness and contrast of the image
visibility factors
sets the midpoint of the range of brightness visible in the digital image. in CT, it determines the midpoint of the range of CT numbers to be displayed
window level (WL)
a control that adjusts the radiographic contrast on the digital image. In CT, it adjusts how many CT numbers are visible in the image
window width
visibility factors of a quality radiograph include
brightness and contrast
this results in poor quality digital image because of improper processing due to extreme over exposure to the image receptor
saturation
what feature provides a numeric value indicating the level of radiation exposure to the digital image receptor
exposure indicator
anatomic tissues that attenuate the x-ray beam equally are said to have this
low subject contrast
an imaging system that can resolve 10 Lp/mm instead of 6 Lp/mm is said to have this
improved sharpness
unwanted scatter exposure to the image receptor will likely increase this
fog
what is defined as “the range of exposure intensities an image receptor can accurately detect”
dynamic range
for a given field of view, a large matrix size will result in this
more pixels
in digital imaging, which of the following determines the range of grayscale available for display
pixel bit depth
during digital image display, the contrast can be lowered by increasing this
window width
the ability of the imaging system to distinguish between small objects that attenuate the x-ray beam similarly defines this
contrast resolution
increasing the displayed field of view for a fixed matrix size will result in this
increased pixel size
the visibility of anatomic structures is increased with this
increased CNR and increased SNR
an imaging system with a higher detective quantum efficiency (DQE) does this
more efficient in converting x-ray exposure to a quality image
double exposing an image receptor will likely result in this
image artifact
