Contrast Flashcards
Arrt f/s
scale of contrast
Refers to the number of densities visible (or the number of shades of gray).
Arrt f/s
long scale
Term used when slight differences between densities are present (low contrast) but the total number of densities is increased.
Arrt Film screen
contrast
Radiographic contrast is defined as the visible differences between any two selected areas of density levels within the radiographic image.
Arrt f/s
short scale
Term used when considerable or major differences between densities are present (high contrast) but the total number of densities is reduced
Arrt f/s
film latitude
The inherent ability of film to record a long range of density levels on the radiograph.
Film latitude and film contrast depend upon the sensiometric properties of the film and processing conditions, and are determined directly from the H and D curve.
ARRT f/s
Film Contrast
The inherent ability of the film emulsion to react to radiation and record a range of densities.
Arrt f/s
exposure latitude
The range of exposure factors which will produce a diagnostic radiograph.
Arrt f/s
subject contrast
The difference in the quantity of radiation transmitted by a particular part as a result of the different absorption characteristics of the tissues and structures making up that part.
Arrt digital radiography
contrast
Image contrast of display contrast is determined primarily by the processing algorithm. The default algorithm determines the initial processing codes applied to the image data.
Arrt digital radiography
scale of contrast
Is synonymous to “gray scale” and is linked to the bit depth of the system.
Gray scale is used instead of scale of contrast when referring to digital images.
Algorithm
Mathematical codes used by the software to provide the desired image appearance.
Arrt digital radiography
dynamic range
The range of exposures that may be captured by a detector. The dynamic range for imaging is much larger than film.
Arrt digital radiography
receptor contrast
The fixed characteristics of the receptor. Most digital receptors have an essentially linear response to exposure. This is impacted by contrast resolution (the smallest exposure change or signal difference that can be detected.)
Ultimately, contrast resolution is limited by the dynamic range and the quantization (number of bits per pixel) of the detector.
Arrt digital radiography
exposure latitude
The range of exposures which produces quality images at appropriate patient dose.
Arrt digital radiography
subject contrast
The magnitude of the signal difference in the remnant beam.
Windows level
Identifies the brightness of the type of tissue imaged.
Window width
The gray scale representation of the tissue.
The wider the window width, the longer the gray scale.
What factor affect contrast
kVp Grids Processing IR speed Subject Beam restriction
Contrast resolution means
The smallest exposure changes and signal differences that can be detected
Quantization
Number of bits per pixel
Dynamic range
Range of values over which a system
Low contrast aka
Long scale
Reduced contrast
Diminished contrast
High kVp exposure gives — contrast
Low contrast
If there are lots of shades of gray, the image is —- contrast, and —- scale.
Low contrast
Long scale
If there are less density differences on an image, it is —- contrast
Low
Low kVp exposure produces —- contrast
High
High contrast aka
Short scale contrast
Increasing contrast
If there are fewer shades of gray between black and white the image is —– scale contrast
Short
If there are big density differences on the image, it is —contrast
High
What controls the penetrability of the beam
kVp
A thicker object density will produce
Less density on the image
Long scale contrast with have a —- straight line portion on an HD curve.
Flatter
A steeper straight line portion of the HD curve means
Short scale/ high contrast
A sensiometric strip is created with
Stepwedge
Penetrometer
The thinner end of the stepwedge will create more —- on the strip.
Density / blackness
The function of contrast
To make detail visible
Fog will — contrast
Decrease
Contrast aka
Density differences
Factors that do not influence contrast
mA
Time
SID
Factors that influence contrast in f/s and digital
kVp Subject IR Collimating Beam restriction Grid Compression
Factors that influence contrast in f/s
Chemical processing
Intensifying screen
Film speed
Factors that influence contrast in digital
IR
Digital processing
Bit depth
Increasing kVp from 80 to 95 will effect contrast how?
More long scale
Low contrast
Changing from no grid to 8:1 grid will effect contrast how?
More short scale
High contrast
If chemistry was hot, adding chemical fog to film
More long scale
Low contrast
Change from 200 speed screen to CBH and correct mAs will effect contrast how?
More long scale
Low contrast
As screen speed increases then
Contrast increases
Higher contrast
Shorter scale
As grid ratio increases then
Contrast increases
Shorter scale
Higher contrast
As speed screen decreases
Contrast decreases
Going from no cone to extended cone will effect contrast how?
Increase contrast
Why does adding an extension cylinder increase contrast
Less scatter is produced
Why does adding compression increase contrast/more short scale
Less matter less scatter
A patient with osteoporosis will —contrast. Why?
Increase contrast/more short scale
Because the part is less dense; so image is more black and white
( this pathology needs less kVp)
Do a patient with ascites
More long scale
Because more matter, more scatter; it needs more kVp
The more you collimate
Less scatter
Less grey
Short scale contrast
Higher contrast
Bit depth
How many bits you are stacking
Stacking of digital brightness
Define aerial beam/remnant beam
The beam that emerges from the body.
What is subject contrast and what does it contain
The contrast in the remnant beam.
Contains wanted information derived from the patient
And also unwanted information–scatter.
4 factors that affect subject contrast
Radiation Quality
Radiographic Object
Scatter Radiation
Fog
How does radiation quality affect subject contrast
⬆️ kVp = ⬆️ penetrating ability
Thereby producing a longer scale of contrast
⬇️ contrast
Radiographic object means
Body part
Thickness
Nature of part: tissue density and pathology-additive and destructive
Name 5 radiographic objects ranging from greatest to least radiopacity
- Tooth enamel
- Bone
- Tissues of H2O density such as muscle, glands, liver, spleen, pancreas, kidney
- Adipose tissue
- Gas/ air filled structures
Scatter is
A noise factor obscuring information or detail
Impairs contrast by a fogging affect
Scatter radiation can be controlled by
Beam restriction and grid
Fogging
From any other source, contributes to noise.
Imparting an overall grey appearance to the image and reducing contrast
—-interferes with our ability to see something
Scatter
Is subject contrast is unaffected by
The type of image receptor used to create image
Image receptor contrast includes 3 components
Film/Screen combinations
Development Process
Digital Systems
Image receptor contrast
F/S combinations;
Film emulsions are designed by manufacturers to
Display different scales of contrast
Depends on facility’s body parts imaged
Intensifying Screens convert what?
Over 98% of X-ray photons to light
Why does the IS conversion process enhance contrast
Because S/F is designed to respond to the light emitted by the IS
As film-screen system speed ⬆️ then contrast
As film-screen system speed ⬆️ then contrast ⬆️ (shorter scale), and latitude ⬇️ (less steps in the range).
Image Receptor Contrast
Development Process
What affects contrast
Different chemicals/ingredients within the developer; excess chemical ⬆️ fog and ⬇️ contrast.
Excessive temperature or other processor problems; ⬆️ temperature ⬆️ fog ⬇️ contrast
Image Receptor Contrast
Development Process
How do you ensure optimum quality
Daily sensitometry
Strict adherence to QC
Bushong defines Contrast Resolution as
The ability to distinguish anatomical structures of similar subject contrast
All digital systems have better ——- than F/S systems.
Contrast resolution
Windowing
Changing the image brightness and/or contrast scale
Why doesn’t doubling mAs change gray scale?
Because every step gets twice as dark, but the density differences between the steps has not changed.
When is contrast ideal?
When you see what you need to see
When would you want long scale contrast
To see detail; and subtle changes in density
Histograms and LUTS in digital systems
Is the recipe card; processing algorithms
Differential absorption
Different degrees of X-ray absorption based on the body tissue and densities and thickness
it determines subject contrast
If you need to produce the same OD at a slightly reduce contrast scale
5% rule
5% rule
⬆️kVp 15% and ⬇️ mAs 30%
If image has too many gray/ long scale, or too black and white
Apply 15% change while either 1/2 or double mAs
4 factors that RT must judge
Anatomical part
Body habitus
Suspected pathology
X-ray IR characteristics
Pixel represent a
BIT
4 factors that RT must judge
Anatomical part
Body habitus
Suspected pathology
X-ray IR characteristics
Pixel represent a
BIT
Image contrast is a result of which
- Differential tissue absorption
- Atomic number of tissue being traversed
- Proper regulation of mAs
- Differential tissue absorption
2. Atomic number of tissue being traversed
In comparison with 60kV, 80 kV will?
- Permit greater exposure latitude
- Produce more scatter radiation
- Produce shorter scale contrast
- Permit greater exposure latitude
2. Produce more scattered radiation
Which of the following technical changes would best serve to remedy the effect of very different tissue densities?
- Use of a small focal spot
- Use of a high ratio grid
- High kilovoltage exposure factors
- High MAS
- High kVp
A 15% decrease in kilovolt age accompanied by a 50% increase in MAS will result in?
- Shorter scale of contrast
- Increase in exposure latitude
- Increase in radiographic density
- Decrease in recorded detail
Shorter scale of contrast
Under exposure of a radiograph can be caused by all of the following except insufficient
- mA
- Exposure time
- KVp
- SID
SID
Insufficient SID will result in increased exposure rate and radiographic overexposure.
All The following have an impact on contrast except?
- Photon energy
- Grid ratio
- OID
- Focal spot siz
Focal spot size
An increase in kilovoltage will serve to produce — scale contrast
Long
Brightness and contrast resolution in digital imaging can be influenced by
- Window level
- Window width
- Look up table
All of them
Which of the following are associated with subject contrast?
1 patient thickness
2. Tissue density
3. Kilovoltage
All of them
As kilovoltage increases, beam attenuation is decreased and subject contrast
Decreases
As grid ratio is decreased the scale of contrast becomes
Longer
As window level increases
Brightness increases