Term
| Average energy of a filtered bremsstrahlung spectrum is ____ to ____ the maximal energy. |
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Definition
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Term
| How much of the incident electron energy on the target electrode is converted to heat? |
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Definition
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Term
| The ratio of radiative energy loss from bremsstrahlung to collisional energy loss is |
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Definition
Ek*Z / 820,000
Ek - kinetic energy in keV
Z - atomic number |
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Term
The most common target electrode material is _____?
The atomic number is _______? |
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Definition
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Term
| The K shell binding energy of Tungsten. |
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Definition
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Term
| In X-ray tubes, characteristic K x-rays are produced only when |
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Definition
| The energy of the incident electron is greater than the K shell binding energy. |
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Term
| The three primary selectable parameters on the x-ray control panel are |
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Definition
| kVp, mA and exposure time |
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Term
Typical x-ray voltages for diagnostic imaging,
for mammography |
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Definition
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Term
| Typical x-ray tube current for fluoroscopy and projection radiography |
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Definition
Fluoro - 1 to 5 mA
Projection Radiography - 50 to 1200 mA |
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Term
| The cathode is the ________ electrode and consists of a _______ and a _________ ______________ |
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Definition
negative electrode
filament and a focusing cup |
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Term
| Typical voltage and current used in the filament circuit. |
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Definition
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Term
| The process of electrons being released from the filament caused by the filament current heating the filament. |
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Definition
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Term
| Purpose of the focusing cup |
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Definition
| It shapes the electron distribution |
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Term
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Definition
| The voltage across the x-ray tube isn't large enough to overcome the electric field from the cloud of electrons around the cathode. Further increasing the filament current does not increase the tube current. |
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Term
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Definition
| The filament current directly determines the x-ray tube current. |
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Term
| What is a grid-biased x-ray tube. |
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Definition
| A large negative voltage of about -4,000 V can be applied to the focusing cup to stop the flow of electrons. This provides a means to rapidly switch the x-ray output on and off. |
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Term
| The anode is maintained at a ________ potential. |
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Definition
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Term
| Advantages of a Tungsten anode. |
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Definition
High atomic number - provides more efficient x-ray production
High melting point - provides better heat loading |
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Term
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Definition
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Term
| Advantage of a rotating anode over a stationary anode. |
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Definition
| Higher heat loading and higher x-ray intensity output. |
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Term
| Focal spot dimensions are determined by |
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Definition
| the filament length in one direction and the width of the electron distribution (controlled by the focusing cup) in the perpendicular direction. |
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Term
| The anode target angle is defined as |
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Definition
| the angle between the anode target surface and the central ray of the x-ray beam. |
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Term
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Definition
| 7 to 20 degrees with 12-15 being most common |
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Term
| According to the line focusing principle, the effective focal spot length is given by |
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Definition
effective length = actual length * sin Θ
θ is the anode angle |
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Term
| Advantage & disadvantage of large focal spot |
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Definition
Advantage - higher power loading so more x-rays can be generated
Disadvantage - lower spacial resolution |
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Term
| Advantage and disadvantage of a larger anode angle |
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Definition
Advantage - larger anode angle gives a larger field of view
Disadvantage - it also results in a larger effective focal spot - so resolution isn't as good |
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Term
| Nominal focal spot size (length and width) is specified where? |
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Definition
| Along the central ray of the x-ray beam. |
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Term
| The effective focal spot length shortens in the ______ direction. |
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Definition
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Term
| The width of the focal spot changes in which direction? |
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Definition
| The width of the FS does not change with position in the x-ray field. |
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Term
| Tools for measuring focal spot size include |
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Definition
| pinhole camera, slit camera, star pattern and bar pattern. |
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Term
| NEMA requires focal spots to be measured at |
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Definition
| 75 kVp and 50% of the maximal rated mA |
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Term
What is the heel effect?
What causes it? |
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Definition
The reduction in x-ray intensity toward the anode side of the x-ray field.
Caused by attenuation from the anode itself. |
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Term
| When is the heel effect less prominent? |
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Definition
| When using a longer source-to-image distance (SID) or smaller fields of view. |
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Term
| Typical large and small focal spot sizes. |
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Definition
Large - 1.2 mm
Small - 0.6 mm |
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Term
| The x-ray tube insert consists of |
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Definition
| cathode, anode, rotor assembly and support structure sealed in a glass or metal enclosure under high vacuum. |
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Term
| Leakage radiation exposure rate is limited to |
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Definition
| 0.88 mGy air kerma per hour (100 mR/h) at 1 m from the focal spot |
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Term
| Leakage technique factors are |
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Definition
| Maximal operable kVp at the highest possible continuous current (typically 3 to 5 mA) |
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Term
| The light field and x-ray field must be aligned such that |
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Definition
| the sum of the misalignments in either the length or the width is within 2% of the SID. |
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Term
| Two types of filtration in an X-ray tube. |
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Definition
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Term
| Inherent Filtration consists of |
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Definition
| The glass or metal insert at the x-ray tube port, housing oil, and field light mirror. |
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Term
| X-ray tube ports are typically made of |
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Definition
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Term
| Mammography X-ray ports are made of |
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Definition
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Term
| Added filtration is usually made of |
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Definition
| Aluminium, copper or plastic |
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Term
| Mammography filters are typically made of |
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Definition
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Term
| What is the purpose of added filtration? |
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Definition
| To absorb low energy x-rays that have little chance of penetrating the patient, thus reducing patient dose. |
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Term
| Transformers in x-ray generators do what? |
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Definition
| Convert low voltage (480 V) into high voltage (20,000 to 150,000 V) using electromagnetic induction. |
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Term
| What is the Law of Transformers |
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Definition
Voltage change is proportional to the ratio of the number windings.
Vp/Vs = Np/Ns
p - primary coil, s - secondary coil |
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Term
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Definition
Allows current to only flow in one direction,
converts an AC current into a DC current |
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Term
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Definition
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Term
|
Definition
Watts (J/s)
also
1 Watt = 1 Volt * 1 ampere |
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Term
| Power is the rate of _______ production or expenditure. |
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Definition
energy
(Units of energy is the Joule) |
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Term
| How is secondary current determined in a transformer? |
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Definition
Power in = Power out
VpIp = VsIs
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Term
| An increase in voltage across a transformer results in a ___________ in __________. |
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Definition
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Term
| At the operator's console, the technologist can select; |
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Definition
| tube voltage (kVp), tube current (mA), exposure time (s) or the product of mA and time (mAs), the AEC mode and the focal spot size (large or small) |
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Term
| In flouroscopy, the automatic exposure rate control circuit is called? |
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Definition
| ABC - automatic brightness control |
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Term
| Types of X-ray generators include |
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Definition
| single-phase, three-phase, constant potential, and high-frequency. |
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Term
| The most common x-ray generator is the |
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Definition
| high frequency generator. |
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Term
| Drawbacks of a constant-potential generator. |
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Definition
| Very costly and requires a lot of space. |
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Term
| Voltage Ripple is defined as |
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Definition
| % V ripple = (Vmax - Vmin) / Vmax * 100 |
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Term
| Voltage ripple for a singe-phased, self rectified, generator is |
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Definition
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Term
| Typical voltage ripple for a medium-high frequency inverter generator. |
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Definition
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Term
| Purpose and other name for a countdown timer. |
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Definition
| Aka, backup timer. Used as a safety mechanism to terminate the x-ray exposure in the case of an exposure switch failure. |
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Term
|
Definition
| AEC - Automatic exposure control |
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Term
| Purpose of the phototimer |
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Definition
| Measure radiation incident on the image receptor and terminate the x-ray production when the proper exposure is reached. |
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Term
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Definition
| Maximal power that an x-ray tube focal spot can accept or the generator can deliver. |
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Term
| What is the benchmark for power rating? |
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Definition
100 kV and the maximum tube current available for a 0.1 sec exposure
Power (kW) = 100 kV * I (Amax for a 0.1 s exposure) |
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Term
Typical Power Ratings for
1.2 mm FS
0.6 mm FS
0.3 mm FS |
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Definition
1.2 - 80 to 100 kW
0.6 - 30 to 50 kW
0.3 - 5 - 15 kW |
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Term
Define a Heat Unit
What is the formula. |
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Definition
Expresses the energy deposition on the Anode
For single phase: Energy (HU) = peak voltage (kVp) * tube current (mA) * exposure time (sec)
For 3 phase to constant potential - multiply by 1.35 to 1.4 |
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Term
| How is the Heat Unit defined for fluoroscopy? |
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Definition
It is defined in terms of HU rate.
HU/s = kVp * mA |
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Term
| The SI unit of energy is the |
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Definition
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Term
| Energy deposited in the anode in Joules is given by |
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Definition
| Energy (J) = RMS Voltage (VRMS) x tube current (mA) x exposure time (s) |
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Term
| The relationship between deposited energy in joules and HU is given by |
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Definition
| Energy (HU) = 1.4 x Heat Input (J) |
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Term
| In anode cooling, the radiative cooling rate is proportional to |
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Definition
| T4 where T is absolute temperature |
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Term
| Three terms that descibe the output of an X-ray tube. |
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Definition
| Quality, Quantity, and Exposure |
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Term
| The Quality of an X-ray beam describes? |
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Definition
| The ability to penetrate, higher energy beams have higher quality. |
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Term
| The Quantity of an x-ray beam refers to? |
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Definition
| The number of photons that are present. |
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Term
| The Exposure of an x-ray beam refers to? |
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Definition
| The amount of electrical charge produced per unit mass of air. |
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Term
| X-ray production efficiency, quality, quantity, and exposure are determined by what six factors? |
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Definition
| Target material, tube voltage, tube current, exposure time, beam filtration, and generator waveform. |
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Term
| How does the anode target material affect x-ray output. |
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Definition
It affects the quantity of bremsstrahlung photons (higher Z is more efficient).
It affects the quality because of the characteristic x-rays.
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Term
| How does the tube voltage affect x-ray production? |
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Definition
1. quantity - increased efficiency with higher voltages
2. quality - maximum energy of the bremmstrahlung spectrum changes with tube voltage |
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Term
| How does exposure vary with kVp. |
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Definition
Exposure is proportional to kVp2.
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Term
| To acheive equal transmitted exposure through a typical patient, how does mAs vary with kVp? |
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Definition
mAs varies with the 4th to 5th power of the kVp ratio.
(kVp1/kVp2)5 * mAs1 = mAs2 |
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Term
| How does the tube current affect x-ray output? |
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Definition
| The quantity of x-rays is directly proportional to tube current. |
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Term
| How does the exposure time affect x-ray output? |
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Definition
| The quantity of the x-rays is directly proportional to exposure time. |
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Term
| How does beam filtration affect x-ray output. |
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Definition
1. quantity - it removes low energy x-rays so increasing filtration decreases quantity.
2. quality - by removing low energy x-rays the average energy increases so the quality increases. |
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Term
| When did HVL requirments change? |
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Definition
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Term
| How does the generator waveform affect x-ray output? |
|
Definition
| It affects both the quality and the quantity. |
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Term
| X-ray beam quantity is approximately proportional to? |
|
Definition
|
|
Term
| X-ray beam quality is dependent on? |
|
Definition
| Tube voltage, beam filtration, anode target material and generator waveform |
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Term
| X-ray tube exposure depends on |
|
Definition
| both x-ray beam quantity and quality. |
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