how easily details can be seen on a radiograph
radiographic quality
what 3 things affect detail/ quality
radiographic desity, contrast, and geometric factors
what are the 3 geometric factors
magnification, distortion, un-sharpness
what color do x-rays turn film
black
what can cause un-sharpness
patient moving, wrong SID
what does increasing mAs, kVp, developing time, temperature of developer do
create greater density
what can influence density
tissue density and patient thickness
what does decreasing SID do to density
increases it
what is inversely proportional to tissue density
radiographic density
the higher the tissue density, the___ the radiographic density
lower
if thickness of tissue doubles, x-rays reaching film is
halved
what primarily controls radiographic contrast
kVp level
difference in density and mass between 2 adjacent anatomical structures
subject contrast
what causes film fog
light exposure
what does not affect contrast
SID
high contrast=short scale=black to white= low kVp when radiographing what
bone
low contrast=long scale=gray tones=high kVp when radiographing what
soft tissue
what do you do if film background is grey
increase mAs by 30-50%
what does “overexposed” mean
too dark
what do you do if overexposed but bones are white
decrease mAs by 30-50%
what do you do if overexposed and bones are grey
decrease kVp by 10-15%
what does “underexposed” mean
too light
what do you do if underexposed but anatomic silhouetes are not visible
increase kVp by 10-15%
what do you do if underexposed and anatomic silhouetes are visible
increase mAs by 30-50%
how do you evaluate a radiograph
look at background, look at overall, expose with new exposure factors
what does scatter do to a radiograph
darkens film, inappropriate areas of film is exposed
radiation reflected from behind image plane back o image
backscatter
how can you control backscatter
collimate beam, lead foil backed cassettes
what is used to radiograph thicker body parts without all the scatter
a grid
where is the grid
under the table between patient and film
what is the thickness of the grid strips
0.5 mm
how many strips are in a grid
500-1500
what can spacer material be made of
fiber, aluminum, plastic
what are the lead strips lined up with
primary beam
how much can a grid reduce scatter
85-95%
distance from tube to grid
grid focus
decrease intensity near edges of grid due to absorption of primary beam
grid cutoff
what is caused by misalignment of the grid
grid cutoff
how do you get rid of grid cutoff
adjust SID
ability of grid to absorb scatter
grid effeciency
what is determined by height, thickness, and number of lead strips
grid efficiency
relation of the height of the strip to the distance between them
grid ratio
what grid absorbs more: 12:1 or 6:1
12:1
number of lead strips per cm area of grrid
lines per centimeter
more lines per centimeter means they are
thinner/absorb less
increase amount of exposure due to primary beam being absorbed
grid factor
orientation of lead strips and their longitudinal axis
grid pattern
what grid pattern is most common
linear
what grid has a higher grid ratio
crossed= double grid ratio
what grid pattern absorbs more scatter
crossed
what grid pattern cannot be used with oblique views
crossed
lead strips angled slightly to line up with the primary beam
focused grids
what grid type is most common
focused
lead strips parallel the whole way across
unfocused grid
what is used for smaller structures due to absorbing more x-rays
unfocused grids
what grid type is used in human and specialized large animal facilities
potter-bucky diaphragm
what grid type moves back and forth during exposure
potter-bucky diaphragm
what can large focal spot, motion, screens and film cause
geometric un-sharpness
variation in normal size and shape due to relation to x-ray source and film
geometric distortion
3 types of geometric distortion
magnification, elongation, foreshorting
what geometric distortion is often seen with severe hip dysplasia
foreshortening
measurable/visible difference between 2 radiographic densities
contrast
what primary exposure factor controls scatter
kVp
on a radiograph, what color is soft tissue
shades of grey
on a radiograph, what color is bone
white
on a radiograph, what color is gas/fluid
black
on a radiograph, what color is air
black
on a radiograph, what color is lead
clear
on a radiograph, what color are metals
white
used to describe image sharpness, clarity, distinctness, and perceptibility
radiographic detail
high contrast=___scale
short
low contrast=___ scale
long
increased number of grey tones=
long scale of contrast
black and white radiograph=
short scale of contrast
