Radiographic density is defined as the degree of blackness on the radiograph.
What is radiographic contrast?
Radiographic contrast is defined as the density difference between two areas of a finished radiograph (If the diffrence between two areas is great, the contrast is high. if there is a slight difference in density, the contrast is low.)
What mainly affects radiographic density?
mAs
What mainly affects radiographic contrast?
kVp
True or False:
Does higher kVp increase scatter radiation?
true
What two questions should be asked when evaluating radiographic technique?
1. Is the film too light or dark?
2. Is there proper penetration?
What does an overexposed radiograph look like?
The radiograph is too dark, and either the kVp or mAs should be decreased
What does an underexposed radiograph look like?
The radiograph is too light, and either the kVp or mAs should be increased
If penetration is inappropriate, should mAs or kVp be increased?
kVp
What to do when a radiograph is too light, and there is adequate penetration?
Increase mAs by 30-50%
For example, if you can see the anatomic parts clearly in an abdominal shot, but there lacks density (overall blackness).
What to do when a radiograph is too light, and there is inadequate penetration?
increase kVp by 10-15%
For example, if you can't see the anatomic parts clearly in an abdominal shot.
Does a high kVp result in a high or low contrast?
As a general rule, high kVp results in low contast- a gray radiograph.
What to do when a radiograph is too dark, and there is no over penetration?
Decrase mAs by 30-50%
For example, if upon examination of an abdominal radiograph, the spine and pelvis are relatively white compared with surrounding soft tissues indicates adequate pentration, but there is excessive density on the film (organs are hard to distinguish).
What to do when a radiograph is too dark, and there is over penetration?
Decrase kVp by 10-15%
For example, if upon examination of an abdominal radiograph, the spine and pelvis are gray (bone density) indicates overpentration.
What does a quality radiograph consist of?
A quality radiograph consist of adequate penetration, sufficient density, and good contrast.
What kind of contrast is desirable for a soft tissue radigraph?
low contrast (many shades of gray), so you want a high kVp.
What kind of contrast is desirable for bone tissue radigraphs?
high contrast is desirable (more white and black), so you want a low kVp.
What is radiographic quality?
Radiographic quality refers to how easily details can be perceived on a radiograph.
What does radiographic quality depend on?
radiographic density, contrast, and geometric factors.
What makes a radiograph black?
x-rays!
radiographic density is inversely porportional to tissue density.
In other words, if the density or thickness of tissue double, the number of x-rays reaching the film is approximately halved.
What is contrast? radiographic contrast? subject contrast?
Contrast is defined as the visible diffrence between two adjacent radiographic densities.
Radiographic contrast is the density difference between two adjacent areas on a radiograph.
Subject contrast is defined as the difference in density and mass between two adjacent anatomic structures (tissue densities)
What does mAs affect?
mAs affects the quantity of the x-rays and is the primary factor that affects density.
Scatter radiation is non-image-forming radiation that is scattered in all directions as a result of objects in the path of the beam.
Scatter radiation cuases contrast to decrease.
What is the function of a grid?
A grid is a device placed between the patient and the radiographic film that is designed to absorb scatter radiation.
What is the Focal Point for a grid?
The center point of the grid is the focal point.
What determines grid efficiency?
The height, thickness, and number of lead strips determines grid efficiency
what is grid ratio?
The relation of the height of the lead strips to the distance between them, is the grid ratio.
As the grid ratio increases, so does the grid efficiency.
Why are the lines per centimeter important in a grid?
More lines per centimeter in a grid means the lines are narrower.
As the lead lines decrease in width, the grid is less efficient in the absorption of higher energy scatter radiation.
What is grid factor?
Grid factor is used when forming a technique chart, in order to compensate for part of the main beam being absorbed by the grid.
what are the diffrent grid patterns?
Linear Grid: parallel, focused, and pseudofocused
Crossed Grid
A focused grid is made up of lead strips that are angled slightly so that they focus at the central point of the grid.
T/F: A focused grid is designed to be used with any source image distance (SID)
F, such grids are to be used at a specifeid source-image distance, with some allowance for variation in distance from the manufacturer's recommendations.
The grid must not be placed upside down= grid cutoff
What is an unfocused grid?
An ufocused grid is one in which the lead strips are parallel.
when an unfocused grid is used with a short focal-grid distance, grid cutoff occurs.
What is radiographic detail?
The definition of the edge of an anatomic structure on a radiograph.
radiograph quality?
The ease with which details can be perceived on a radiograph.
What are some reasons for loss of detail?
motion, large focal spot size, or a decreased SID, mixed up screen/film combos
what are some examples of geometric distortion
elongation and foreshortening from the object being radiographed is not parallel
magnification from using an incorrect SID
What is the function of the developer in film processing?
The developer is a chemical solution that converts the latent image on a film to a visible image.
the primary function of the developer is to convert the exposed silver halide crystals to black metallic silver.
What is the function of the rinse bath in film processing
the rinse bath stops the developing process and prevents carryover contamination to the fixer.
What is the function of the fixer in film processing
The unexposed silver halide crystls remaining on the film are unaffected by the developer solution and must be removed.
the fixer serves two basic purposes:
1. it clears the unexposed silver halide crsystals from the film and
2. it hardens the gelatin coating so that it can be dried without damaging the film surface
What is the function of the wash bath in film processing
The purpose of the wash is to remove the processing chemicals from the film surface.
If a film is not washed propely for a long enough period, the image will eventually discolor and fade.
