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Rad Imaging I
Terms in this set (112)
mA or milliampere
The unit of measure for the amount of current flowing from cathode to anode within the x-ray tube.
What is "fog"?
It is the result of scattered photons interacting with the image receptor; it is additional density without any useful information.
The loss of energy from the x-ray beam as it passes through tissue due to interactions between the x-ray photons and the tissue.
The emission of electrons (ion) as a result of heat (therm). The heating of the filament is due to the application of current. Boiled off electrons from the filament.
Computed Radiography or CR
A digital radiographic system that uses imaging plates within cassettes.
The instantaneous emission of light from a material due to the interaction with some type of energy.
A dynamic imaging process allowing imaging of movement.
Reddening and burning of the skin, an early and less serious effect of exposure to large doses of x-radiation.
How is a radiographic image formed?
It's formed as a result of differential absorption; some of the x-ray beam is absorbed in tissue and some is transmitted. This variation in beam exiting the part will represent the area being imaged.
Half Value Layer or HVL
The amount of filtration needed to reduce the intensity of the x-ray beam to half of its original.
Anode and Cathode
Anode is the positive side of the x-ray tube, cathode is the negative side. The cathode contains the filament.
Can x-rays travel around corners?
X-rays travel in straight lines, they are unable to travel around corners.
How does the image appear?
The latent (invisible) image occurs first and then, after proper processing, the manifest (visible) image appears.
What percentage of x-ray beam actually reaches the image receptor?
Less than 5%
Results when no interactions occur between the x-ray photon and tissue.
Consisting of both transmitted and scatter radiation, exits the patient in the direction of the image receptor.
Photon or quantum
A small, discrete bundle of energy.
What does increasing the kilovoltage (kVp) do?
It increases the speed of the electrons traveling between cathode and anode and results in an x-ray beam with greater penetrability.
Are x-rays electrically positive, negative, or neutral?
What happens at a higher kilovoltage (energy)?
Fewer photon interactions occur, resulting in more x-ray photons being transmitted.
What is the maximum amount of leakage radiation from an x-ray tube?
100 mR/hr when measured at a distance of 1 meter.
What does beam filtration do?
It results in removing lower energy x-ray photons, resulting in an x-ray beam with fewer photons but with a higher average energy; increase beam quality.
What is the speed of light?
3 x 10^8 m/sec or 186,000 miles/sec.
It's the exact area on the focal track of the anode target where electrons strike.
Wavelength and Frequency
Inversely related; as one increases, the other decreases.
How does chemical change occur in radiographic or photographic film?
The result of exposure to ionizing radiation.
The measure of mA that flows from cathode to anode.
What is the photoelectric effect dependent on?
Both energy of the x-ray photon and the composition of tissue.
What effect does using a grid have on contrast?
It increases contrast.
For a given exposure, what does increasing part thickness do?
It decreases radiographic density.
If a person stands 12 feet from the source of exposure, receives an exposure of 16 R/min, and then moves to 3 feet from the source of exposure, what would be the new exposure rate according to the inverse square law?
If the first radiograph of a chest is done using 72 inches and 12 mA's and a second radiograph is done using 40 inches, how much mA's should be used to maintain density?
If a person stands 3 feet from the source of exposure, receives an exposure of 16 R/min, and then moves to 6 feet from the source of exposure, what would be the new exposure rate according to the inverse square law?
If the first radiograph of a foot is done using 4 mAs at 40 inches and a second radiograph is done using 50 inches, how much mAs should be used to maintain density?
Considering the primary controller of radiographic density, which film has the greatest density?
mA x time
What kVp and mAs should be used in order to reduce patient exposure?
Higher kVp and lower mAs.
If mAs were fixed, what kVp would produce the greatest density?
The highest kVp.
What is the minimum change in mAs that would result in a visible change in radiographic density?
When imaging the thoracic spine, in order to take advantage of the anode heel effect, the most superior portion of the patient's spine should be placed beneath:
The anode end of the tube.
The radiographer should adjust mAs by a factor of 2 for how many centimeters of thickness?
What film (mAs) would have the greatest density considering the primary controller of radiographic density?
mAs (mA x time).
A quality radiograph is done using 10 mAs, 70 kVp, and a 12:1 ratio grid. How much mAs is needed to produce an image with the same density when the grid is removed?
What does not affect radiographic density until adequate penetration is reached?
What does a change in mAs result in?
Results in a direct change in radiographic density.
What does kilovoltage have an inverse relationship with?
What does changing the kVp by 15% do?
It will have the same effect on density as changing the mAs by a factor of 2.
What needs to be adjusted when changing the SID, OID, grid and/or film-screen speed?
An adjustment in mAs to maintain density.
What is radiographic quality?
It's a combination of both the visibility (photographic properties) (density & contrast) and the sharpness (geometric properties) of recorded detail.
Digital imaging and density
For digital imaging, factors that change the quality and/or quantity of the x-ray beam will not have the same effect on density.
What is radiographic density?
It is the amount of overall blackness produced on the image after processing and is controlled by the milliamperage and exposure time selected.
Speed of film-screen system and density
The greater the speed of the film-screen system, the greater the amount of density produced on the radiograph; the lower the speed of the film-screen system, the less density produced on the radiograph.
Hypersthenic Body Habitus
These individuals have thicker part sizes compared with sthenic or hyposthenic individuals, so exposure factors are higher.
Asthenic Body Habitus
A very slender body habitus. Exposure factors are lower.
kVp and contrast media
The radiographer should select a high kVp (90 and above) for barium sulfate studies and a medium kVp (70 to 80) for procedures requiring iodinated solutions.
Additive, destructive pathologies, & technical factors
It is necessary to increase kVp when radiographing parts that have been affective by additive diseases and to decrease kVp when radiographing parts that are affected by destructive diseases (i.e. emphysema).
Grid Ratios: GCF (Grid Conversion Factor):
No Grid = 1
5:1 = 2
6:1 = 3
8:1 = 4
12:1 = 5
16:1 = 6
If mAs were fixed, which kVp would produce the greatest density?
The highest kVp
If kVp were decreased by 15% and no changes were made to mAs:
Density would decrease & contrast would increase.
What happens to mAs if kVp were decreased by 15% & density needed to be maintained?
Use twice the mAs.
The exposure time for radiograph of chest on an infant:
The shortest exposure time.
If a radiograph needs to be repeated due to it being too dark, what is the minimum change to mAs?
Reduce mAs by 50%
What happens to contrast & density when SID is decreased?
Density is increased and no change in contrast.
What should be adjusted if optical density needs to be changed?
What happens to patient dose when mAs is increased from 20 to 40?
Patient dose will be doubled.
An image with low contrast appears:
A radiograph with few densities but great differences among them is said to have:
What will reducing the area of exposure (increasing collimation), do to image contrast?
Increase image contrast.
An abdomen image is done using 66 kVp and 40 mAs. Image density is appropriate but the image has too high (short scale) contrast. How would you come up with the best change?
Increase kVp by 15% then 1/2 the mAs. This is because the abdomen is longer-scale. Ex: 76 kVp and 20 mAs.
Image-forming x-rays include those which have been:
Transmitted without interaction & scattered through Compton interaction.
Compton scatter contributes to:
Decreasing the kVp will increase:
Patient dose; scatter=patient absorption, alara=lower mAs, lower mAs=higher kVp.
What DECREASES when photoelectric interactions INCREASE?
What INCREASES when scatter radiation INCREASES?
The x-rays that are transmitted through the patient without interaction contribute to:
The most commonly used beam restricting device is the:
What does lowering the kVp do to patient dose and to image contrast?
It increases patient dose and image contrast. kVp & image contrast have an inverse relationship.
What improves contrast and reduces patient dose?
What is increased when beam penetrability is increased?
A radiograph taken using 65 kVp @ 10 mAs is too light. What technique would double the optical density while producing a wider scale of contrast?
75 kVp @ 10 mAs.
Which technique would give the highest patient dose?
mA x time (mAs)
What is defined as the ability to image two separate objects and visually detect one from the other?
The technologist primarily controls radiographic contrast by varying the:
Optical density is primarily controlled by the:
Which kVp setting will provide the most kinetic energy to filament electrons?
The highest kVp.
Between 50 to 80 kVp, which is capable of producing the lowest contrast?
Why is scatter radiation exposure undesirable?
Because it decreases contrast.
What is the x-ray absorbing material in grids?
Collimation acts to reduce scatter and its resultant image fog primarily by:
Limiting area of exposure.
A positive contrast media will have what effect on radiographic contrast?
What does increasing mAs do to beam QUALITY and beam QUANTITY?
There's no change to beam quality but an increase in beam quantity. Quality=energy, quantity=mAs.
If mAs is increased from 20 mAs to 40 mAs, the patient dose will:
A radiograph is taken using 75 kVp @ 20 mAs. Which change in technique would increase contrast but maintain the same density?
65 kVp @ 40 mAs. Double mAs to maintain density.
What medical condition may require a lower technique?
High kilovoltage results in:
More densities, resulting in low-contrast (long-scale).
Low kilovoltage results in:
Fewer densities, resulting in high-contrast (short-scale).
Image receptor with wide latitude:
Can be used over a greater range of exposures.
A radiograph with long scale contrast will have:
Wide latitude & low contrast.
A beam restricting device.
Compression device & contrast:
Changes in kVp effect:
Image noise, optical density, & image contrast.
Three factors that influence scatter:
kVp, field size, & patient thickness.
What percent x-ray beam incident transmitted through patient?
0% to 9%
How is contrast resolution improved?
By lowering kVp, patient compression, & tight collimation.
The most kinetic energy uses the highest....
Increase when kVp is decreased.
PBL - Positive Beam Limitation
Collimated to IR size.
66 kVp @ 40 mAs to what change to increase contrast?
76 kVp @ 20 mAs.
The use of a grid device reduces scatter produced? True or false?
False (due to stupid produced word).
Has lead lines that are angled, or canted, to approximately match the angle of divergence of the primary beam; allows more transmitted photons to reach the IR.
Grid ratio for kVp of 100?
What happens to density when 9x9 IR is changed to a 14x17 IR?
What happens to mAs from 2.5 when SID goes from 72" to 60"?
What does a periapical radiograph show?
radiographic examinations of the salivary glands using contrast medium is called?
What are the common causes of Secondary Osteoporosis?
Which type(s) of contrast media is(are) required for CTA?
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