Unit 1 Flashcards
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Discuss the “dual nature” of electromagnetic radiation.
This is a property of x-rays in that x-rays act like waves and like particles; waves because they have measurable wavelengths and frequency, however, they behave more like matter when they interact with matter.
Explain the relationship between electromagnetic energy, frequency and wavelength.
Decreasing the wavelength/increasing the frequency increases the electromagnetic energy.
Compare the velocity, frequency and wavelength of high energy x-rays with low energy x-rays.
X-rays have a constant velocity in a vacuum (the speed of light). The high energy x-rays have higher frequency/shorter wavelength, while the low energy x-rays have lower frequency and longer wavelength.
When were x-rays discovered?
November 8, 1895
In what year were some of the biologically damaging effects of x-rays discovered?
1898
X-rays were discovered in experiments dealing with electricity and….
vacuum tubes
X-rays were discovered with they caused a barium platinocyanide coated plate to…
fluoresce
X-radiation is part of which spectrum?
Electromagnetic
X-rays have a dual nature, which means that they behave like both…
waves and particles
The wavelength and frequency of x-rays are ____ related.
inversely
What electrical charge do x-rays have?
None
What is the mass of x-rays?
They have no mass
The x-ray beam used in diagnostic radiography can be described as being…
polyenergetic
Define electromagnetic radiation
Radiation that has both electrical and magnetic properties
Define fluorescence
Instantaneous production of light resulting from the interaction of some type of energy and some element or compound.
Define frequency
The number of waves passing a given point per given unit of time.
Define photon
A small discreet bundle of energy.
Define quantum
A small discreet bundle of energy
Define wavelength
The distance between two successive crests or troughs in a wave.
The 14 characteristics of x-rays
invisible electrically neutral no mass travel speed of light in vacuum can't be optically focused form polyenergetic (heterogeneous) beam can be produced in a range of energies travel in straight lines can cause some substances to fluoresce cause chemical changes in radiographic film can penetrate human body can be absorbed or scattered in human body can produce secondary radiation can cause damage to living tissue
Actual focal spot size
The size of the area on the anode target that is exposed to electrons from the tube current. Actual focal spot size depends on the size of the filament producing the electron stream.
Added filtration
The filtration that is added to the port of the x-ray tube.
Anode
A positively charged electrode within the x-ray tube composed of a tungsten alloy. It consists of a target and, in rotating anode tubes, a stator and rotor.
Anode heel effect
The x-ray beam has greater intensity (# of x-rays) on the cathode side of the tube, with the intensity diminishing toward the anode side. The anode heel effect occurs because of the angle of the target.
Cathode
A negatively charged electrode (within the x-ray tube). It comprises a filament and a focusing cup.
Compensating filter
Special filters added to the primary beam to alter its intensity. These types of filters are used to image anatomic areas that aren’t uniform in makeup and assist in producing more consistent exposure to the image receptor.
Dosimeter
A device that measures x-ray exposure.
Effective focal spot size
Focal spot size as measured directly under the anode target. It is affected by the angle of the anode.
Exposure time
The length of time that the x-ray tube produces x-rays. It is set by the radiographer & is measured in milliseconds as a fraction or decimal.
Filament
A coiled tungsten wire that is the source of electrons during x-ray production.
Filament current
Heats the tungsten filament. This heating of the filament causes thermionic emission to occur.
Focusing cup
Made of nickel and nearly surrounds the filament. It is open at one end to allow electrons to flow freely across the tube from cathode to anode. It has a negative charge, which keeps the cloud of electrons emitted from the filament from spreading apart. it focuses the stream of electrons.
Half-value layer
(HVL) The amount of filtration that reduces the intensity of the x-ray beam to one half its original value is considered the best method for describing x-ray quality. It is expressed in millimeters of aluminum.
Heat unit
(HU) The amount of heat produced from any given exposure.
Inherent filtration
Filtration that is permanently in the path of the x-ray beam. Three things contribute to this: 1) the glass envelope, 2) the oil that surrounds the tube & 3) the glass envelope in the tube housing.
Kilovoltage
(kVp) Set by the radiographer and applied across the x-ray tube at the time the exposure is initiated, kVp determines the speed at which the electrons in the tube current move. It also affects the quantity of x-rays.
Leakage radiation
any x-rays, other than the primary beam, that escape the tube housing.
Line focus principle
Describes the relationship between the actual and effective focal spots in the x-ray tube. A smaller target angle produces a smaller effective focal spot.
Milliamperage
(mA) The unit used to measure the tube current.
Off-focus radiation
Occurs when projectile electrons are reflected and x-rays are produced outside the focal spot.
Rotor
A device in the x-ray tube that causes the target to rotate rapidly during x-ray production.
Space charge
The electrons liberated from the filament during thermionic emission that form a cloud around the filament.
Space charge effect
The tendency of the space charge not to allow more electrons to be boiled off of the filament.
Stator
An electric motor that turns the rotor at a very high speed during x-ray production.
Target
A metal that abruptly stops electrons in the tube current, allowing the production of x-rays.
Thermionic emission
The boiling off of electrons from the cathode filament.
Total filtration
The sum of the x-ray tube’s added and inherent filtration.
Trough filter
A double-wedge compensating filter added to the primary beam to produce more consistent exposure to the image receptor.
Tube current
The flow of electrons from cathode to anode, measure in milliamperage (mA).
Voltage ripple
The amount of consistency in voltage waveforms during x-ray production.
Wedge filter
The most common type of compensating filter. The thicker part of the wedge filter is lined up with the thinner portion of the anatomic part that is being imaged, allowing fewer x-ray photons to reach that end of the part.
X-ray emission spectrum
The range and intensity of x-rays emitted.
What is the source of electrons during x-ray production?
The filament.
What is the part of the anode that is struck by the focused stream of electrons coming from the cathode, which stops the electrons and creates the production of x-rays?
The target.
What is the rotating anode made of? Why?
Tungsten. It has a high melting point and high atomic number.
What happens on the cathode and anode sides when the prep button is activated?
Cathode: Filament current heats filament, electrons are boiled off the filament (thermionic emission), the electrons gather together around the filament (space charge), the negatively charged focusing cup keeps the electron cloud focused together, the number of electrons in the space charge is limited (space charge effect).
Anode: The rotating target begins to turn rapidly, quickly reaching top speed.
After activation of the rotor, what happens on the cathode and anode sides when the exposure is initiated?
Cathode: High negative charge strongly repels electrons, these electrons stream away from the cathode and toward the anode (tube current).
Anode: High positive charge strongly attracts electrons in the tube current, the electrons strike the anode, x-rays are produced.
What direction do electrons flow in the x-ray tube?
From cathode to anode. This is called the tube current & is measured in milliamperes (mA).
How much of the kinetic energy is converted to heat and how much is converted to x-rays?
> 99%
<1%
If you increase the kilovoltage what happens to the speed of the electrons traveling from the cathode to the anode (tube current)?
It also increases.
As the milliamperes are increased what happens to the quantity of the x-rays produced?
It also increases.
What does the line focus principle describe?
It describes the relationship between the actual focal spot, where the electrons in the tube current hit the target and the effective focal spot, the same area as seen from directly below the tube.
How are heat units calculated?
HU=mA x time x kVp x generator factor
Electrons interact with what to produce x-rays and heat?
Target
The cloud of electrons that forms before x-ray production is referred to as what?
Space Charge
The burning or boiling off of electrons at the cathode is referred to as what?
Thermionic emission
Which primary exposure factor influences both the quality and quantity of x-ray photons?
kVp
The unit used to express tube current is what?
mA
what percentage of kinetic energy is converted to heat when moving electrons strike the anode target?
> 99%
The intensity of the x-ray beam is greater on which side of the tube?
The cathode side
According to the line focus principle, as the target angle decreases what happens?
The effective focal spot decreases
How much mAs is produced when the radiographer sets 70 kVp, 600 mA and 50 ms?
30 mAs
Increasing the kVp results in what?
x-rays with higher energy and more x-rays
Total filtration in the x-ray beam includes what?
inherent filtration and added filtration
How many heat units result from an exposure made on a single phase x-ray unit using 400 mA, 0.2 second and 70 kVp?
5600 HU
Describe the relationship kilovoltage has on the x-ray beam.
Higher kilovoltage (kVp) increases the speed of the electron beam, which increases the penetrability of the x-ray beam. The lower the kVp, the slower the electron beam and the less penetrable the x-ray beam.
Describe the relationship milliamperage has on the x-ray beam.
The more the milliamperage, the higher number of electrons in the tube current and the more x-rays are produced. The lower the mA, the fewer the electrons in the tube current and the fewer x-rays produced.
Describe the relationship exposure time has on the x-ray beam.
Exposure time is the number of seconds (or milliseconds) that the tube can produce x-rays. The longer the exposure time, the higher the number of x-rays produced. The shorter the exposure time, the lower the number of x-rays produced.
Describe the relationship mAs has on the x-ray beam.
If the mAs (milliamperage x seconds) is higher, the number of x-rays produced is higher. If the mAs is lower, the number of x-rays produced is lower.
Absorption
As the energy of the primary x-ray beam is deposited within the atoms comprising the tissue, some x-ray photons are completely absorbed. Complete absorption of the x-ray photon occurs when it has enough energy to remove an inner-shell electron. (photoelectric interaction)