Term
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Definition
from kinetic energy given to E- as they accelerate through an electric potential (i.e. from cathode to anode)
kinetic energy then gets converted to electromagnetic energy |
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Term
| WHEN AN ACCELERATING E- INTERACTS W/ TARGET ATOM, THERE ARE 3 POTENTIAL INTERACTIONS: |
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Definition
1.Energy transferred to E- of atom which excites them to another level – this is typically low energy
2.Energy transferred to atom which ejects the electron (aka IONIZATION) – emits X-rays
3.Energy transferred decelerates E- but does not excite or remove E- from atom |
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Term
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Definition
MAIN INTERACTION USED TO CREATE RADIATION IN THE X-RAY TUBE
“decelerated radiation”
E- decelerates as it travels through target material as it exchanges kinetic energy for electromagnetic energy (which are x-ray photons)
Results in POLYENERGETIC X-RAYS |
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Term
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Definition
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Term
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Definition
specific area from which the majority of x-rays originate
Increasing FSS – increases amount of heat absorbed
Decreasing FSS – improves resolution
FSS doesn’t affect contrast or pt dose
Typical FSS for CT is 2.5 mm |
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Term
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Definition
low energy photon excites an atom but passes through w/o any net transfer of energy
the scattered photon has the same energy of the incident photon but in a different direction
minimal significance in radiology |
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Term
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Definition
incident photon interacts with a bound outer shell e-
e- is ejected from atom and photon is scatter with reduction in energy and change in direction
scattered photon may interact with surrounding tissues or reach image receptor where it degrades image quality
Energy of scattered photon increases as angle of deflection decreases
Energy of incident photon = energy of scattered photon + energy of ejected e-
Accounts for most of the scattered radiation in diagnostic radiology
probability of this interaction increases w/ number of outer shell e- (increased density of material) and decreases with increasing incident photon energy |
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Term
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Definition
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Term
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Definition
removal of photons from a beam as it passes through matter
caused by both absorption and scattering of primary photons |
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Term
| Linear Attenuation Coefficient |
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Definition
(u) - fraction of photons interacting per 1-unit thickness of material
indicate rate at which photons interact as they move through material; inversely related to average distance traveled before interacting |
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Term
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Definition
thickness of material required to reduce intensity of beam to 1/2 initial value
indirect measure of photon energy/quality of the beam
HVL = 0.7/u |
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Term
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Definition
Increases Mag
Decreases Scatter |
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Term
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Definition
Reduces visibility of low contrast objects
Increased by increasing contrast and by image subtraction
Decreased by increasing noise |
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Term
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Definition
Visibility of anatomic detail
Radiography provides highest resolution |
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