ch 26-27-28-29physics Flashcards
which of the 2 image properties determines if the IR was sufficiently exposed?
density
structural details are made up of ________ and _______.
density and contrast
density is considered an ______ _______ _______.
image quality factor
are brightness and density interchangeable?
no
a monitor control function that can change light and dark on an image on the display monitor
brightness
with film and digital radiography the key to a visible image is….
having the correct IR exposure
window level controls
brightness
when the IR receives too many photons and records to much information it is called
overexposure
when the IR did not receive enough information it is considered
underexposed
what is the controlling factor of density for film and digital radiography?
mAs
with film we need to adjust mAs _____% to see a visible change in density
30
why must we monitor density with the Ei number?
because regardless of the exposure the computer system will attempt to rescale the histogram so the images acceptable to the eyes
what is the general rule of thumb for density
make changes in increments of doubles or halves
what is the primary influencing factor of density?
mAs
in what two ways does kv alter the intensity of the beam that reaches the IR?
controls the energy of the e- that strike the anode
controls the average energy of the X Ray photons produced at the anode target
a change in kv alters the intensity of the beam when mAs and other factors _____ ______ ______.
stay the same
what is the minimum change in kv to see a noticeable change in density ? the recommended?
5%. 15%
when is the 15% rule used?
when you want to change the contrast of an image but keep the same density
what factor do you adjust if you only want to change density only?
mAs
what are the OTHER influencing factors for density?
focal spot size only from blooming anode heel effect distance filtration beam restriction anatomical part grid IR film speed
what makes up the detail of an image?
contrast
the difference between adjacent densities/IR exposure?
contrast
define dynamic range:
contrast as it is displayed on a monitor in digital imaging
“range of brightness”
what digital process controls brightness on a digital image?
window width
what affects grayscale bit depth?
contrast/dynamic range/ ww on the z axis
why is contrast hard to adjust?
because any change in density will effect contrast
why is low contrast often desired?
it has more differences in density
what are the two properties that make detail visible ?
density and contrast
how do we manipulate contrast in film?
digital?
kvp
ww
what are the 2 types of contrast?
IR contrast ( film/ digital)
subject contrast
these make up IMAGE CONTRAST
what are the 4 factors that can affect IR contrast in film?
intensifying screen
film density
d log e curve
processing
digital IR contrast:
as digital images go through post processing both the _______ and the ______ affect the final image contrast displayed
histogram and LUT
note: the correct mAs and kvp must be chosen by the tech to ensure the correct exposure to the IR and desired differential attenuation
define subject contrast:
the range of differences in the intensity of the X Ray beam AFTER attenuation
subject contrast depends on:
kv, amount and type of tissue radiated
higher kvp produces _____ contrast
decreased
what type of interaction creates decreased contrast
Compton
digital scatter causes ______ contrast
decreased
how does AMOUNT of irradiated material affect contrast?
affects the number of X rays that reach the IR
the anatomical structures of interest are visible only when ________ ________ exists between the densities
sufficient contrast
what type of interaction causes high contrast
photoelectric interactions
discerning contrast is difficult if an image has poor ___ _________
IR exposure/ density
in digital, KVP can no longer be assessed by viewing the difference between densities or brightness……why?
the response curve is LINEAR
what is the controlling factor of contrast?
main influencing factor ?
kvp
mAs
OTHER influencing factors of contrast:
focal spot size (not likely )
anode heel effect. (very little effect)
distance filtration beam restriction anatomical part grid f/s combo processing
what 3 things determine the actual recorded detail
matrix size
pixel size
grayscale bit depth
