Mod 2 - Image Acquisition and Technical Factors
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Comprehensive flashcards covering kVp, mAs, SID, grids, and Exposure Indicator (EI) concepts from the Image Acquisition and Technical Factors lecture notes.
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60 Terms
What does kVp stand for?
Kilovoltage Peak.
What does kVp measure?
The electrical force (potential difference) between the cathode and anode.
What causes electrons to travel from the cathode to the anode?
The kVp applied across the tube.
What happens when electrons strike the anode?
X-ray photons are produced.
Why is the term "peak" used in kVp?
Because it represents the maximum energy of the x-ray beam.
Is the x-ray beam homogeneous (elements that are all of the same kind, nature, or character)?
No, it contains photons with different energies.
What does kVp primarily control?
Beam quality and penetrability.
Increasing kVp increases what property of the beam?
Penetrating power.
Which technical factor controls beam strength?
kVp.
Which technical factor controls beam quantity?
mAs.
Every body part is assigned a kV range based primarily on what?
Body part thickness.
As body part thickness increases, what happens to the kV range?
It increases.
Can different body parts of the same thickness use similar kV ranges?
Yes.
Within a recommended kV range, where should the technologist generally work?
Near the upper end of the range.
Why is it beneficial to work near the upper end of the kV range?
Less mAs is needed.
Why does using less mAs support ALARA?
It reduces patient dose.
What does ALARA stand for?
As Low As Reasonably Achievable.
What happens if kVp is increased beyond the functional range?
The beam becomes excessively penetrating.
Why is excessive kVp undesirable?
It reduces tissue interactions and subject contrast.
What happens to image contrast when kVp is too high?
Contrast decreases.
Why are tissue interactions important?
They create subject contrast.
What happens when too many photons pass through the body without interaction?
Diagnostic contrast is lost.
When might a technologist intentionally work in the lower portion of the kV range?
When tissue density is decreased.
What pathology is specifically mentioned as requiring lower kVp?
Osteoporosis.
Why may lower kVp improve visualization in osteoporosis?
Less penetration is required and pathology may be better demonstrated.
What does mAs stand for?
Milliampere-seconds.
What two factors make up mAs?
Milliamperage (mA) and exposure time (seconds).
What does mAs control?
The quantity of x-ray photons produced.
What happens when mAs increases?
More photons are produced.
What happens to patient dose when mAs increases?
Patient dose increases.
Which technical factor most directly affects patient radiation quantity?
mAs.
Which body part generally requires higher mAs: chest or abdomen?
Abdomen.
Why does the abdomen require higher mAs?
It contains more tissue and causes greater attenuation.
Why does the chest require lower mAs?
It contains large amounts of air and less tissue attenuation.
Can two body parts have the same thickness but require different mAs?
Yes.
Besides tissue composition, what other major factor affects mAs?
Patient thickness.
As patient thickness increases, what happens to mAs requirements?
mAs must increase.
Why do thicker patients require more mAs?
More tissue absorbs and attenuates photons.
What does SID stand for?
Source-to-Image Distance.
What happens to photon concentration when SID increases?
It decreases.
Why does photon concentration decrease when SID increases?
Beam divergence spreads photons over a larger area.
When SID increases, what technical factor must usually be increased?
mAs.
Does increasing SID decrease photon energy?
No.
What decreases when SID increases?
The quantity of photons reaching the receptor.
Which factor remains unchanged when SID changes?
kVp.
What is the primary purpose of a grid?
To remove scatter radiation.
How does scatter radiation affect image quality?
It reduces radiographic contrast.
Why does using a grid require increased mAs?
The grid absorbs some primary photons along with scatter.
What does EI stand for?
Exposure Indicator.
What does the EI number represent?
The amount of radiation that reached the imaging receptor.
A technologist increases kVp from 70 to 95. What happens to beam penetrability?
It increases.
A technologist increases SID from 100cm to 180cm. What technical factor will likely need adjustment?
mAs must be increased.
Two patients have identical abdominal thicknesses. One has severe osteoporosis. Which patient may require lower kVp?
The osteoporotic patient.
An image appears to have poor subject contrast because the beam passed through tissues too easily. What technical factor was most likely excessive?
kVp.
Which body part generally requires greater mAs: chest or abdomen?
Abdomen.
A grid is added for an abdomen projection. What technical factor adjustment is required?
Increase mAs.
A student states that EI reflects patient dose. Is this correct?
No.
What does EI actually measure?
Radiation reaching the detector.
Can incorrect centering affect EI values?
Yes.
Can poor collimation produce misleading EI values?
Yes.