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61 Cards in this Set

  • Front
  • Back
Most electron interactions are __?__
Brems (Bremsstrahlung interaction)
Diagnostic energy range is
30 kvp to 150 kvp
Below 70 kVp, with a tungsten target, ______% of the x-ray beam consists of brems inBreteractions.
100%
Above 70 kVp, with a tungsten target, _______% of the beam consists of brems interactions.
85%
Bremsstrahlung Interaction
Occurs when a projectile electron completely avoids the orbital electrons of the tungsten atom and travels very close to its nucleus. This causes the electron to suddenly "slow down"
Characteristic interactions
Produced when a projectile electron interacts with an electron from the inner shell (K-shell) of the tungsten atom.
The average energy of Brems is _?_
1/3 of the maximum kVp used
Energy emitted from a characteristic interaction is __?__
Emitted as xray photons
Below 70 kVP, _______ characteristics interactions are in the xray beam
no characteristic interactions
Above 70 Kvp, approximately ___% of the xray beam is characteristic interactions.
15%
Characteristic xrays have an effective energy of _?_
69 keV
Average energy of Brems is ......?
1/3 of the maximum kVp used
Characteristic interactions
Projectile electron interacts with electron from the inner shell (K shell) of the tungsten atom
The electron in the characteristic interaction must have _?_
Must have enough energy to eject the K-shell electron from its orbit
When a K-shell electron is ejected from its orbit .......?
An outer shell electron drops into the open position and releases a binding energy
Below 70 kVp _____ characteristic xrays are in the beam
No - none
Above 70 kVp approximately _______ characteristic xrays are in the beam.
15% are characteristic
Consists of wide range of energies
Polyenergetic
The lowest energies in the xray emissions spectrum are always _?_
15 to 20 keV
The highest energies in the xray emissions spectrum are _?_
Equal to the kVp set on the control panel
The xray emission spectrum is affected by:
kVp
mA
Filtration
Target material
Voltage waveform
What effect does an increase in mA have on the emission spectrum?
Results in a proportional change in the amplitude at all energies.
What effect does an increase in kVp have on the emission spectrum?
Results in an increase in amplitude at all energies but a greater increase at high energy - the spectrum is shifted to the right or high energy side.
What effect does an increase in added filtration have on the emission spectrum?
Increase in the average energy of the xray beam and a reduction in xray quantity
What effect does an increase in the atomic number of the target material have on the emission spectrum?
The spectrum shifts to the right, slight increase in amplitude
What effect does an increase in mA have on the emission spectrum?
Results in a proportional change in the amplitude at all energies.
What effect does an increase in kVp have on the emission spectrum?
Results in an increase in amplitude at all energies but a greater increase at high energy - the spectrum is shifted to the right or high energy side.
What effect does an increase in added filtration have on the emission spectrum?
Increase in the average energy of the xray beam with an accompanying reduction in xray quantity
What effect does an increase in the atomic number of the target material have on the emission spectrum?
The spectrum shifts to the right, slight increase in amplitude
As the voltage across the xray tube increases from zero to its peak value ........??
The xray intensity and energy increase slowly at first and then rapidly as peak voltage is obtained.
An increase in current (mAs) results in _?_
Results in an increase in quantity. No change in quality.
An increase in voltage (kVp)
Results in an increase in quantity and quality
An increase in added filtration
Results in a decrease in quantity and an increase in quality
An increase in the target atomic number (Z)
Results in an increase in quantity and quality
An increase in the voltage ripple
A decrease in quantity and quality
Quality of the xray beam refers to the _?_
Penetrating power of the primary beam (kVp)
Quantity of the xray beam refers to the _?_
Number of xray photons in the primary beam. (mA)
The speed of an electron is determined by _?_
kVP
Energy of electrons is ___________ to kVp setting
Directly proportional
Higher kVp results in
Greater penetrability
Higher kVp results in ?
Faster tube current from anode to cathode
Kilovoltage reading must be accurate within _?_
+/- 5%
Quality and quantity of xray photons are better with _?_
Minimal voltage ripple
Used to measure tube current
mA (milliamperage)
The number of xrays produced is __________ to mA
Directly proportional
Timer accuracy can vary _________ for times >10ms and _________ for times <10ms.
+/- 5% for >10ms
+/- 10% for <10ms
Exposure time
-Determines length of time that the xray tube produces xray photons
-Expressed in seconds or milliseconds, fraction or decimal
Exposure time and number of xrays are ____________ proportional
Directly
Three QC tests to evaluate radiation output my measuring radiation intensity
1 - Reproducibility of exposure
2 - mAs reciprocity
3 - Milliamperage & exposure time linearity
Reproducibility of Exposure
Verifies the consistency of radiation output for a given set of exposure factors. Max can vary +/-5%
mAs Reciprocity
Verifies the consistency of radiation intensity for changes in mA and exposure time with constant mAs. Max can vary +/- 10%
Milliamperage and exposure time linearity
Verifies that proportional changes in mA and/or exposure time will likewise change the radiation intensity - doubling the mA or exposure time should double the radiation intensity - max variation of +/-10%
Xray intensity is less on the _____ side of the tube
Anode
Thicker parts should be placed on the ______ side of the tube.
Cathode
Xrays that exit tube are polyenergetic
-Difference energy levels; low,med,high
-Low are of no diagnostic use, increase patient dose
Added filtration
-Added to the port of the tube
-Aluminum mostly used
Inherent filtration
-Permanently in path of xray beam
-Glass envelope, oil in tube, mirror in collimator
Total filtration
Sum of the added and inherent filtration - usually 2.5mm
Government guidelines state that ________ of aluminum or its equivalent is required total filtration for tubes operating above 70 kVp
2.5mm
Half value layer
-Amount of filtration that reduces intensity of beam by half of the original value
-Measured in mm-AL
Dosimeter
A radiation measuring device