Image Aquistion Flashcards
matrix size and pixel size relationship
inversely related
FOV and pixel size relationship
direct
pixel size and resolution relationship
inversely related
small pixel size and resolution
small pixel size has a high resolution
what pixel size has a 512X512 matrix with a 20 cm FOV
.40 mm/pixel
change 20 to mm then take 200/512 =.39
how do you find the pixel size
units?
take the FOV (mm) and divide it by the matrix (FOV/matrix)
units: mm/pixels
pixel depth
dynamic range
how many shades of gray
bit size equation
so a 6-bit =
2^n
6 bit = 2^6 = 64
spatial resolution is measured in?
line pairs/mm
lp/mm
matrix is made up of
columns and rows
what does filtration do to the intensity of the beam?
decreases it bc there are less photons
moire effect definition:
when is the moire effect seen
having wavy lines
seen when using stationary grids
grids are composed of
lead
aluminum
plastic fibers
kVp and contrast relationship
inversely related
what pulse does CT use?
short pulse
mAs and density
higher mAs has higher density
the component of a CR IP that records the radiologic image
PSP
PSP’s store what kind of image
how long does it store it for
latent
8 hours
DXA is used to see
bone mineral density
radiation dose in DXA
low
the luminescent light emitted by the PSP is transformed into the image seen on the CRT by the
ADC
insufficient back up time would have what effect on the image
underexposed
focal spot size is measured by what tests
pinhole camera
slit camera
star pattern type
kVp and exposure rate relationship
direct bc an increase in kV (photon energy) will result in a greater number (exposure rate) of scattered photons
as field size decreases, scatter ______, and image quality _______.
scatter decreases
image quality increases
what is very important when using AEC
accurate positioning
the negative aspect of CR
has a limited spatial resolution
best spatial resolution
film screen
windowing refers to
changing the image brightness and/or contrast
changes in window width
changes number of grays, which is contrast resolution
changes in window level
changes the image brightness
FOV describes how much ____ is included in the ____
pt
matrix
foreshortening can be caused by
angling the part
elongation can be caused by
angling the tube
size distortion is aka
magnification
each cm increase in pt thickness requires what adjustment to kVp?
increase 2 kV to the exposure
what is the proper way to store film screen inventory (if you were stocking) bc
upright bc if they are stacked on top of each other there is a loss of contrast
what contributes to film fog?
the age of the film
excessive exposure to safelight
processor chemistry
outdated film will have what kind of contrast
loss of contrast, which causes fog
photon energy and wavelength relationship
inverse
as kV is increased, more high energy photons are produced, the overall energy of the beam is increased. so the wavelength is decreased
an increase in mA does what to the number of photons produced at the target
increases
for an abdomen xray, which needs more exposure, supine or erect? why?
erect because everything in the stomach sits lower when they are standing, whereas when they lay everything spreads out and thickness of the stomach decreases
solid state detector plates (in DR) are made of
barium fluorohalide
height of the lead strips to the width of the interspaces describes
grid ratio
what type of grid ratio allows for more centering latitude?
low grid ratio
high grid ratios need to be accurate
TECHNICAL FACTORS
INCREASE OR DECREASE
TECHNICAL FACTORS
INCREASE OR DECREASE
Ascites
fluid in the abdomen
increase
Osteoporosis
weakening of bone
decrease
Osteomalacia
softening of bones
decrease
Rheumatoid arthritis
hardening of the joints
increase
paget disease
increase
pneumoperitoneum
air in the abdomen
decrease
pneumonia
fluid filled air sacs of the lungs
increase
atelectasis
collapsed lung
increase
emphysema
breaks down air sacs in the lungs
decrease
congestive heart failure
increase
edematous tissue
fluid in the tissues
increase
degenerative arthritis
decrease
atrophic and necrotic conditions
shrinkage or death
decrease
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low ratio grids and high ratio grids allow for how much scatter to reach the IR
low ratio grids allow for a great percentage of scatter to reach the IR
high ratio grids allow for a small percentage of scatter to reach the IR bc it will clean up more scatter
mAs and scatter
no relation
grids and contrast
grids improve contrast
exposure rate is determined by
kV
mA (most)
distance
high kV and scatter
high kV increases scatter
thick/dense structures and scatter
increases scatter
the degree of difference between adjacent denstities
radiographic contrast
mA and contrast
no relation
what is the equation for grid ratio
the height of the strips / the width between them
a 5 in object to be radiographed at 44 in. SID lies 6 in. from the IR. what will be the image width
Image size SID X 44in
__________ = _______ _____ = ______ = 5.78
object size SOD (SOD=SID-OID) 5in 38in
SOD =
SID-OID
in comparison with 60 kV, 80 kV will do what to scatter and exposure latitude
produce more scatter
and
allow for greater exposure latitude (margin of error)
two-dimensional, pixel element, thats measured in XY direction
pixel
how much of the patient is included in the matrix describes?
FOV
mosiaicked
pixelly
misalignment of the tube-part-IR relationship results in
shape distortion (elongation/foreshortening)
focal spot blur is caused by..
the use of a large focal spot
size distortion
magnification
what can cause grid cut-off when using a focused reciprocating grid?
inadequate SID
central ray angulation in the direction of the lead strips causes:
central ray angulation against the direction of the lead strips causes:
in the direction: causes nothing
against the direction: causes grid cut off
phantom images are a result of
incomplete erasure of the previous image on the PSP
what increases the anode heel effect
short SID with large IR
10 degree or less angle
low ratio grids and exposure latitude
low ration grids offer more exposure latitude than high grid ratios
Z direction in a matrix
voxel
volume element
to magnify an object 2X
the OID must be half the distance of the SID
what is the main difference between direct capture and indirect capture DR
direct capture has no scintillator
indirect capture has a scintillator
the direction electrons travel in the xray tube is
cathode to anode
Charges
Anode:
Cathode:
Which way do these charges travel in an xray tube
Anode: positive
Cathode: Negative
Cathode to Anode so negative to positive
when tissue densities are very different (like a chest xray) what can be done to “even out” the densities on the image
increase kV to use a longer scale of contrast (which results in more grays)
for the same FOV, spatial resolution will be improved using..
a larger matrix
or
smaller (NOT FEWER) pixels
matrix and pixel size are inversely related
FOV and resolution relationship
inverse relationship
Decreasing the FOV, decreases the pixel size, which improves resolution
which of the following are methods of limiting the production of scattered radiation and why/why not?
- using moderate grid ratios
- using prone position for abdominal xrays
- restricting the field size
- using prone position for abdominal xrays: because it will compress the stomach, causing less scatter
- restricting the field size: most effective means of reducing scatter
not 1. using grids: because grids cleanup scatter and have nothing to do with the PRODUCTION of scatter
the absorption of useful radiation by a grid is called?
grid cut off
radiographic density is found by what factors?
mAs and distance
high mAs with short distance produces the greatest density
which factor will produce the shortest scale of contrast 70 kV, 8:1 grid 70 kV, 6:1 grid 95 kV, 12: grid 95 kV, 8:1 grid
70 kV, 8:1 grid
want low kVp, bc low kV, high contrast, short scale
and
higher grid ratio cleans up scatter reaching the IR, therefor fewer grays
long scale contrast has___ kV and what type of grid ratio?
high kV, low contrast, long scale
lower grid ratio bc more scatter will reach the IR (producing more grays)
kV and exposure latitude relationship
direct
actual focal spot and effective focal spot size
actual focal spot is larger than the effective/projected focal spot
focal spot blur is greatest at what part of the xray beam
toward the cathode end of the x-ray beam
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mAs and pt dose relationship
direct relationship
IPs can be made from?
carbon fiber
and
magnesium
if the grid failed to move throughout the exposure, how would the image look?
there would be grid lines throughout the image
if the central ray was off center, how would the image look?
it would have a uniform loss of density
the whole image would have a loss of density/ increased brightness
if the SID is above or below the recommended focusing distance, what will the image look like?
there would be an increased brightness/loss of density at its lateral edges
what can be done to reduce the exposure time?
increase mA
or
increase kV
energy and wavelength
inverse
high energy, short wavelength
film processing order
develop, fix, wash, dry
SID and exposure factors relationship
direct
increased SID causes for increased exposure factors (kV or mA)
SID and density relationship
inverse
short SID, more density
Grid cut off is due to
Improper tube and grid alignment
Grid cut off and contrast relationship
Grid cut off increases contrast
the function of the developer in the film processor
change the EXPOSED silver bromide crystals to black metallic silver
quantum noise is due to what factor
whats its appearance
too low mAs
or too much kV
grainy
short SID results in? under/over exposure
overexposure
does the HVL affect tissue density?
no
magnification factor (MF)=
image size/ object size
DR patient dose
low
major advantage to CR
has best/widest dynamic range/latitude
screen speed and contrast
faster the screens the higher the contrast
direct relationship
health informatics aka
ex
health care information technology
PACS
HIS
RIS
the xray image seen on the computer monitor is?
analog image
.3mm or smaller focal spot size is for?
magnification
is the anode heel effect good for….
lateral T-spine
AP femur
RAO sternum
lateral T-spine
AP femur
