Gray Scale (Contrast) Flashcards
Radiographic Contrast
Name and describe 2 photographic factors.
Contrast allows what to be seen but doesn’t change what?
What range is used in digital radiography? What 2 things are they?
Radiographic Contrast
Name and describe 2 photographic factors. Density (overall darkening) & Contrast (visible differences in density)
Contrast allows what to be seen but doesn’t change what? Contrast allows visibility of detail to be seen but doesn’t change structural lines
What range is used in digital radiography? Dynamic range
- What 2 things are they? Window width and gray scale
What is contrast?
Visible differences in shades of density
High vs Low Contrast
High vs Low Contrast
Density Changes
Density Changes
Contrast Changes
Contrast Changes
Contrast and Density
Contrast and Density
What can measure contrast?
A penetrometer or step wedge
High contrast or short gray scale is described as densities with what?
What increases contrast?
High contrast or short gray scale is described as densities with what? Densities with abrupt changes
What increases contrast? Black to white shades
What is low contrast or long gray scale described as?
More shades of grays is what kind of scale?
A long gray scale increases or decreases contrast?
What is low contrast or long gray scale described as? Densities with gradual changes
More shades of grays is what kind of scale? Long scale
A long gray scale increases or decreases contrast? Decreases contrast
Comparison of Gray Scales
Comparison of Gray Scales
Short vs Long Gray Scale
Short vs Long Gray Scale
Contrast Problem
Contrast Problem
Describing Contrast
Describing Contrast
What are the 3 categories of contrast?
- Radiographic Contrast (kVp, air gap grid, etc)
- Subject/Patient Contrast (Pt brings own body tissue, pathology)
- Film/Film Processing Contrast (Type of film and how it was developed)
Radiographic Factors
What is the major controlling radiographic factor?
What does it control?
What effect is created because of this radiographic factor?
What does it do?
This effect will increase as you increase what?
What occurs during the photoelectric effect?
Radiographic Factors
What is the major controlling radiographic factor? kVp
What does it control? Penetration power, energy, and wavelength of primary beam
What effect is created because of this radiographic factor? Compton Effect
What does it do? Creates scatter radiation
This effect will increase as you increase what? Compton effects increases as you increase kVp
What occurs during the photoelectric effect? Absorption of primary beam occurs as you lower kVp
In order to get rid of Compton scatter (fog), what must you do?
Increase kVp
What does a grid do?
What kind of problem do you have if your film is “ugly”?
What does a grid do? Eliminates scatter from reaching IR
What kind of problem do you have if your film is “ugly”? Contrast Problem
What does having an optimal kVp level mean?
What does optimal kVp allow for?
What does having an optimal kVp level mean? Having an appropriate kVp for every body part which will save the patient a radiation dose and for good contrast film
What does optimal kVp allow for? Allows for good penetration for the digital system to have a good signal-ratio signal
What is signal-ratio?
When a film is noisy, it is…
Low noise =
High noise =
Low, grainy film = ___ signal
What is signal-ratio? Radiation converted to a numerical value
When a film is noisy, it is grainy
Low noise = good image
High noise = bad image
Low, grainy film = bad signal
Penetrometer and kVp
Penetrometer and kVp
What 2 things contribute to the overall darkening of an image?
What 2 things contribute to the overall darkening of an image? kVp and density
What is critical for proper density?
If the image is too dark or too light, you cannot judge what on the radiographic image?
What is compromised if the film is overexposed or underexposed?
When talking about contrast problems, what is adjusted so we do not have density problems?
What is critical for proper density? Proper mAs
If the image is too dark or too light, you cannot judge what on the radiographic image? Contrast
What is compromised if the film is overexposed or underexposed? Contrast
When talking about contrast problems, what is adjusted so we do not have density problems? mAs
Why were grids invented?
What do grids improve?
- Higher the grid ratio =
- Lower the grid ratio =
- Higher the grid frequency =
- Lower the grid frequency =
What do you do if you want the patient to absorb more of the beam (ex, kVp too low for a body part)?
Why were grids invented? To stop scatter radiation from reaching the film
What do grids improve? Image contrast
- Higher the grid ratio = increase contrast
- Lower the grid ratio = decrease contrast
- Higher the grid frequency = increase contrast
- Lower the grid frequency = decrease contrast
What do you do if you want the patient to absorb more of the beam (ex, kVp too low for a body part)? Go down in kVp
Nongrid vs Grid
Nongrid vs Grid
What does collimating do?
Collimating does what to the contrast?
The faster the screen speed, the ___ the contrast.
Note: Remember, you can decrease the amount of radiation you use on the fast screen speed.
Faster screen speed = ___ radiation needed = ___ scatter created in patient
What does collimating do? Will help to eliminate scatter radiation from being created plus less scattered reaching the film
Collimating does what to the contrast? Increases contrast
The faster the screen speed, the higher the contrast.
Note: Remember, you can decrease the amount of radiation you use on the fast screen speed.
Faster screen speed = less radiation needed = less scatter created in patient
What does the window level do?
What does the window width do?
What does the window level do? Make image lighter or darker
What does the window width do? Lets shades of gray in
What is needed to reduce the patient’s radiation skin dose and to produce good images?
Filtration
Increased filtration (___ wavelengths) = ___ contrast
Decrease filtration (___ wavelengths) = ___ contrast
Abrupt changes =
What is harder to penetrate? What will you need to do to penetrate it?
Increased filtration (shorter wavelengths) = decreased contrast
Decrease filtration (longer wavelengths) = increase contrast
Abrupt changes = lower kVp
What is harder to penetrate? Barium What will you need to do to penetrate it? Go up in kVp
OID = air gap grid
Increase OID = ___ contrast
Decrease OID = ___ contrast
OID = air gap grid
Increase OID = Increase contrast
Decrease OID = Decrease contrast
If a film is “too contrasty” the film is too…
Too contrast = too much in the differences in the ___ of ___
What do you do to correct the contrast?
What rule to increase kVp?
Whats the rule of thumb?
If a film is “too contrasty” the film is too black and white
Too contrast = too much in the differences in the shades of density
What do you do to correct the contrast? Raise the kVp and lower the mAs
What rule to increase kVp? 15% rule
Whats the rule of thumb? Add 10 kVp or half the mAs
What does it mean if the image is “too flat”?
What do you do to correct the contrast?
What is the % rule?
What is the rule of thumb?
What does it mean if the image is “too flat”? Film is too even in the shades of density/film is too gray in appearance
What do you do to correct the contrast? Lower the kVp and raise the mAs
What is the % rule? 15% rule to lower kVp and double mAs
What is the rule of thumb? Subtract 10 kVp, double mAs
What is inherent in the radiographic film and is influenced by the conditions of the film processors?
What must be followed or you will decrease contrast on the film?
Film speed = ___ vs ___
Slower the speed = ___ contrast
Faster the speed = ___ contrast
What is film latitude?
Slower the film speed = ___ contrast films
Faster the film speed = ___ contrast films
What is inherent in the radiographic film and is influenced by the conditions of the film processors? Film contrast
What must be followed or you will decrease contrast on the film? Film processing
Film speed = slow vs faster
Slower the speed = decrease contrast
Faster the speed = increase contrast
What is film latitude? The ability to record the different shades of density
Slower the film speed = low contrast films
Faster the film speed = higher contrast films
What does H&D curve stands for?
H&D Curve = ___ the ___ contrast
H&D curve is a radiographic relationship between what on the film?
What are other names for H&D?
What does H&D curve stands for? Hurter and Driffield Curve
H&D Curve = plot the film contrast
H&D curve is a radiographic relationship between what on the film? Amount of exposure and the resultant density on the film
What are other names for H&D? Characteristic curve, Sensitometric Curve, or D log E Curve
Name and describe the 3 parts of the curve
**TOE = located in the white area (of x-ray) D min (sensitive minimum)**
• SLOPE = middle of shades of density (how many grays on film)
Average gradient
• SHOULDER = located in the darkest or blackest area (max out at certain darkness)
D max
What is base fog?
Why is the film tinted?
What is base plus fog?
What is base fog? Density already manufactured on film
Why is the film tinted? To reduce eye strain
What is base plus fog? Density that was added to film (becomes part of image)
Name 6 types of patient contrast
- Tissue thickness
- Type of tissue
- Condition of tissue
- Development of tissue
- Tissue densities
- Age of tissue
Name the 10 things x-ray can penetrate from easiest to hardest.
- Gas/Air
- Fat
- Cartilage
- Hollow organs
- Muscle
- Solid organs
- Fluid
- Bone
- Teeth
- Barium
What body habitus is considered to be the norm?
Asthenic habitus is… ___ attenuation of the primary beam so ___ radiation is needed. ___ tissue to interact with ___ compton scatter
Hypersthenic habitus is… ___ attenuation of the primary beam so ___ radiation is needed. ___ tissue to interact with ___ compton scatter
What body habitus is considered to be the norm? Sthenic
Asthenic habitus is extremely thin. Less attenuation of the primary beam so less radiation is needed. Less tissue to interact with less compton scatter
Hypersthenic habitus is massive body build. More attenuation of the primary beam so more radiation is needed. More tissue to interact with more compton scatter
More radiation = ___ compton scatter = ___ grays
If patient absorbs beam, not many shades making it to film
More radiation = more compton scatter = more grays
If patient absorbs beam, not many shades making it to film
Methods to reduce scatter to improve radiographic contrast:
- Removal of scatter radiation through…
- Reduce the amount of tissue being irradiated through…
- Reduce the amount of primary beam needed through…
Methods to reduce scatter to improve radiographic contrast:
- Removal of scatter radiation through use of a grid (>60 kVp or >10cm part) and air gap grid (but will increase magnification)
- Reduce the amount of tissue being irradiated through beam restriction (collimation), proper filtration, and lead blockers (lead glove)
- Reduce the amount of primary beam needed through increasing film/screen speeds (fast the system –> less radiation –> less compton)
What is contrast?
What does is mean when an image has high contrast or short scale? Name 3 characteristics.
What does is mean when an image has low contrast or long scale? Name 3 characteristics.
What is contrast? Differences in shades of density
What does is mean when an image has high contrast or short scale? Abrupt changes in the shades of densitity. Name 3 characteristics. Black to white, low kVp (long wavelenghts), photoelectric effect
What does is mean when an image has low contrast or long scale? Gradual changes in shades of densitiy. Name 3 characteristics. Gray tones added, higher kVp (short wavelengths), compton scatter
Computed radiography is what type of range?
Dynamic range
Density is controlled by window… (brightness)
Contrast is controlled by window… (gray tones)
Density is controlled by window level (brightness)
Contrast is controlled by window width (gray tones)
