week 8: image quality Flashcards
What does a quality image accurately represent?
(1) accurately represents the anatomic area of interest and (2) information is well visualized for diagnosis
What two factors (2 types of resolution) determine the overall quality of the radiographic image?
contrast resolution, spatial resolution
visibility of detail
contrast resolution
sharpness of detail
spatial resolution
image density (optical density or OD): the ____________ represent the ___________ properties of the anatomic part imaged
varying optical densities, attenuation
amount of luminance (light emission) of a display monitor
image brightness
____________ are geometric qualities
Detail and distortion
___________ are photographic qualities
optical density and contrast
spatial resolution is used to evaluate the accuracy of the _____________________
anatomic structural lines displayed
high contrast images display _________________ but ____________
fewer shades of gray but greater differences among them
low contrast images display ________________ but _____________
greater number of gray shades but smaller differences among them
clear area of the image = ___ optical density
low
black area of the image = ____ optical density
high
with digital images, ________ is now the name for optical density
brightness
what is another definition for film densities (Bontrager)?
defined as the amount of “blackness” on the processed radiograph
clear area of the image = ________ brightness
increased
black area of the image = ________ brightness
decreased
optical density and brightness result from the ________ of radiation reaching a particular area
quantity
What is the primary technical factor that controls the amount of OD in an analog image (film/screen image)?
mAs; controls the quantity the reaches the film AND how the manifest image looks
What is the primary factor that controls the amount of OD in a digital image?
mAs; controls quantity that reaches the IR however the computer algorithms control how the manifest images look
true/false: mAs only controls the quantity of photons that reaches the IR/film in analog
false, it controls in both analog and digital systems
in a digital image _______ controls the brightness of the manifest image
computer algorithms
in an analog image __________ controls optical density of the manifest image
mAs
with respect to mAs, kVp, and optical densities/brightness, ______ “controls” and ____ “influences” quantity of photons
mAs, kVp
in an image, low density is _________
increased brightness
in an image, high density is __________
decreased brightness
Radiographic density and tissue density are ___________ to each other
inversely related
increased tissue density will make that particular area on an image _________
brighter/lighter
increased radiographic density will make that particular area on an image ___________-
darker
quantum mottle is due to ___________________; ______ photons and results in _________
insufficient mAs for anatomy of interest, too few, grainy appearance
number of different shades of gray that can be displayed
gray scale
range of shades of gray
scale of contrast
Low scale of contrast, long gray scale = _____________________
many shades of gray, small differences
High scale of contrast, short gray scale = ______________________________
not very many shades of gray; dramatic difference between high and low brightness/densities
What is the primary technical factor that controls the scale of contrast in an analog image (film/screen image)?
kVp
high kVp = ____ scale
low kVp = ____ scale
long, short
What is the primary factor that controls the scale of contrast in a digital image?
kVp
What is the difference between radiographic contrast and subject contrast?
- radiographic contrast = photographic property
- subject contrast = result of the absorption characteristics of the anatomic tissue and the quality of the x-ray beam
what is contrast resolution?
ability to distinguish between objects similar in subject contrast
How should mAs be set to reduce patient exposure?
high mA station, low seconds (reciprocity law)
what is the purpose of filtration of the beam?
remove low energy x-ray photons that have no diagnostic value
what are 2 types of filtration?
inherent, added
what is the type of added filtration?
aluminum
tube filtration (can/can not) be changed
can not
tube filtration is based on _____________
federal regulation standards
increased SID = (more/less) intense beam
less
inverse square law: intensity of the x-ray beam is ___________________ from the source
inversely proportional to the square of the distance
direct law: The mAs/distance compensation formula provides a mathematical calculation for adjusting the ____ when changing the ______.
mAs, SID
increasing or decreasing the kVp by 15% has the same effect as __________________
doubling or halving the mAs
what technical factor is responsible for patient radiation dose?
mAs
what equation interferes with intensity and distance?
inverse square law
