Exposure Flashcards
Define contrast
difference in adjacent densities
Define quantity
The radiation intensity or the number of x rays in the beam, measured in mR
Define the relationship between ma and tube current
Directly proportional
Define the relationship between ma and mR
Directly proportional
Describe the relationship between exposure time and density
Directly proportional
Describe the relationship between time and mR
Directly proportional
Describe the relationship between mAs and density
Directly proportional
describe the relationship between kVp and mR
Inversely proportional
Describe the relationship between SID and mR
inversely proportional
Identify 4 imaging characteristics controlled by SID
magnification, distortion, penumbra and density
Define the reciprocity law.
Any combination of mA and time can be used to get the same mAs with the same result in density.
What is the 15% rule?
If kVp is increased by 15%, mAs will be halved. If kVp is decreased by 15%, mAs will be doubled.
ma + s =
mAs
What is the density maintenance formula?
new mAs/old mAs = new D^2/old D^2
What is meant by low contrast?
lots of gray
What is meant by high contrast?
few shades of gray
How do you get a higher contrast on a film?
lower the kVp
How do you get a lower contrast on a film?
Use a higher kVp
What are the prime factors for exposure?
mA, kVp, distance and time
What is quality?
the penetrability of the beam
What is the controlling factor of contrast?
kVp
What is the controlling factor of density?
mAs
What is the relationship between kVp and scatter?
Directly proportional
What is the function of contrast?
To make details visible
What is meant by short scale contrast?
Few shades of gray
What is meant by long scale of contrast?
Many shades of gray
What is subject contrast?
The range of differences in the intensity of the remnant x ray beam after it has been attenuated by the patient.
What is image receptor contrast?
The range of densities the image receptor is capable of recording.
Five factors that affect image receptor contrast
H & D curve, image density, processing, digital image receptors, intensifying screens
Three factors that affect subject contrast?
kVp, amount of tissue irradiated, type of tissue irradiated.
How does mAs affect radiographic contrast
Under or over exposure
How does focal spot size affect radiographic contrast
No influence.
How does the anode heel effect affect radiographic contrast?
Little effect
How does filtration affect contrast?
Inversely related.
How does beam restriction (collimation) affect contrast?
Inversely related.
How do grids affect contrast?
Directly related.
What are two types of motion?
Involuntary and voluntary.
Give an example of involuntary motion.
pain, breathing, chills, spasms
What is the typical range for O.D?
0.25 to 2.5
How does SID affect density?
By a factor of 4 (inversely).
What are the seven types of radiologic tissue types.
metal, enamel, bone, muscle, fluids, fat and air/gas
Give an example of voluntary motion.
nervousness, discomfort, fear, excitability
Define density.
The overall blackness on the image. Also described as the amount of black metallic silver on a film.
What is fog?
Unwanted density on the film.
The total quantity of x rays produced in an x ray beam is determined by the _____.
mAs
The distance between the x ray tube and the film is?
Source to image distance (SID)
Low radiographic contrast is called?
long scale contrast
Two factors that directly control the amount of x rays emitted by the tube are?
ma and time
The shorter the SID, the __________ the intensity of the xray beam?
greater
Radiographic density if produced by?
The quantity of x rays reaching the image receptor.
Scattered radiation has what effect on radiographic contrast?
It decreases it.
Describe the relationship between filtration and density.
Inversely related.
descibe the relationship between collimation and density
inversely related
Describe the relationship between thickness and density.
Inversely related
Describe the relationship between grid ratio and density.
Inversely related.
Describe the relationship between thickness and contrast.
Inversely related.
Describe the relationship between processing time and contrast
Inversely related.
