week 10: image quality cont. Flashcards
geometric properties of an x-ray is ________________________
how accurately the structural lines are recorded
geometric qualities, degree of sharpness of structural lines
spatial resolution
what is the leading cause of loss of recorded detail?
motion
degree of sharpness of structural lines
spatial resolution
results from radiographic misrepresentation of either the size (magnification) or the shape of the anatomic part
distortion
what is the most common type of motion?
involuntary
small focal spot (decreases/increases) recorded detail
increases
what are the two types of inherent unsharpness
focal spot blur (penumbra), scatter
What is the digital term for a loss of detail?
noise
what is noise?
random fluctuation in the OD of the image
lower noise is __________ contrast and recorded detail
improved
a _____ signal (diagnostic information) to noise (un-diagnostic information) improves contrast and spatial resolution
higher
what are the two types of distortion (general)
size and shape
why is there always magnification in an image?
no anatomy can be directly up against the IR
what do OID stand for?
object to image receptor distance
what do SID stand for?
source to image receptor distance
what do SOD stand for?
source to object distance
what happens when you increase OID?
magnification increases; decreases recorded detail
what happens when you increase SID?
magnification decreases; increases recorded detail
what happens when you increase SOD?
magnification decreases; increases recorded detail
what happens when you decrease OID?
magnification decreases; increases recorded detail
what happens when you decrease SID?
magnification increases; decreases recorded detail
what happens when you decrease SOD?
magnification increases; decreases recorded detail
how is magnification calculated?
magnification factor = SID/SOD
what does 3 part alignment do?
minimize shape distortion
anatomy appears shorter than true object
foreshortening
anatomy appears longer (wider) than true object
elongation
Any misalignment of the CR among the three factors—___________________—will alter the shape of the part recorded on the image receptor.
tube, part, or image receptor
why would we want shape distortion?
limitation of 2D image, can not see all anatomy of interest
how do you get wanted shape distortion?
oblique the patient, axial of CR
barium is considered to be ___________ contrast while air is considered to be ____________
positive, negative
in terms of comparing film and digital contrast resolution, which gives more?
digital gives a higher contrast resolution?
in terms of comparing film and digital spatial resolution, which gives more?
film gives higher spatial resolution
as focal spot size increases, _________ also increases
focal spot blur
