Test 3 Chapters 6-9 Flashcards
Filament current is measured in what?
Amps (A)
Where does filament current occur?
Cathode
Tube current is measure in what?
Milliamps mA
Where does tube current occur?
Flow of electrons from the cathode to anode
Reciprocity in radiology?
Same intensity regardless the time and mA, but the image quality may not be the same.
The anode heal effect becomes more significant when the anode angle increases or decreases?
Increases
Which side of the tube do you want closest to the thickest body part to use the anode heal effect?
Cathode
What does isotopically mean?
X-rays emit in every direction
The (blank) the anode angle the (blank) the effective focal spot, and the more significant the anode heal effect.
Smaller
Large or small focal spot for bone work and why?
Small. You want good detail for bone work (ex: spine)
To convert AC current to near DC current is termed
Rectification
Small or large spot gives you more recorded detail?
Small
Small or large spot can accommodate more heat (bigger body part)
Large
Photon Attenuation
Removal of photons from primary beam
Interactions are total or partial absorption
Photon Transmission
Incident photons that do not interact
Go straight to the image receptor or out the patient body with no change.
Differential Absorption
Attenuation and transmission in tissue that results in the image formation.
Compton interactions…
Contribute to image only in a negative sense “scatter”
Differential absorption is important when subject contrast is low, which means..
Tissues are similar in density and atomic number
What are the 3 factors that influence Differential absorption?
1- Beam energy
2- Atomic number
3- Mass density of matter
Beam Energy: Differential absorption goes Up as Energy goes…
Down
Low energy photons mean what to patient exposure?
Higher patient dose
Atomic number: Differential absorption goes up as atomic number goes…
Up
As atomic number goes up, differential absorption goes…
Up
As atomic number goes up, what happens to the probability of patient exposure?
Goes Up
Are compton interactions influenced by atomic number? and Why?
No, because compton interactions have to do with the actual strength of the photon, the the mass or tissue it’s penetrating.
Mass Density of matter: Differential absorption goes up as density goes…
Up
Mass density of matter is referring to….
Density of body part, not image density
An increase in matter/volume does what to interactions?
Increases them
both Photo Electric AND Compton
Tissue density varies more widely than…
Z -atomic number
mA x kVp =
Watts
mA x kVp/1000 =
kW (kilowatts)
What is a Diode?
X-ray tube with 2 electrodes
Which end of the tube is negative?
Cathode
Which end of the tube is positive?
Anode
Leakage radiation from the X-ray tube housing can not be greater than what?
100 mR per hour at 1 meter
Protective housing on the x-ray tube does what?
Protects from x-ray leakage and electric shock. It also protects the tube itself
Describe filament materials
High melting point, low vaporization
What is the most common cause of tube failure?
2 causes:
- Abrupt: one stupid exposure and the equipment blows up.
- Chronic use: won’t last forever (warm up)
kVp effects quantity above or below the saturation point?
Below
Describe Space Charge Effect
A cloud of negatively charge electrons around the filament repulse continued thermionic emission
Describe the focusing cup
Negatively charged and used to repel electrons toward the anode.
How does the space charge effect thermionic emission?
It limits it.
What controls the propulsion of electrons from the cathode to the anode?
kVp
At what approximate kV range will every electron boiled off propel from the cathode to the anode, leaving none behind-thus no cloud? (aka clean house kV)
110
The closer to the “clean house kV” you get what happens?
The more electrons that transfer from the cathode to the anode, leaving fewer behind in the cloud.
The more electrons you send from the cathode to the anode the more (blank) you get
X-rays
Increase kVp and you increase
Quantity (primarily)
Saturation current is:
the point at which all electrons go from cathode to anode.
Line Focus Principle
Get an effective focal spot size smaller than the actual electron beam with an angled anode.
Anode cooling
How long you have to wait inbetween exposures for the anode to be safely cooled to make more exposures
Why is it important to warm up an X-ray tube?
Prevents damage to “cold” anode from high heat until exposures
Radiographic Rating Charts are used for what purpose?
To determine the safety of a single exposure for a specific x-ray tube. (each tube will have one)
When you do not reach the “clean house” range of kV at the cathode electrons are left behind. The next time you make an exposure the left over electrons will make other electrons boiling off the filament more or less likely to jump off the wire?
Less likely
Tube current does what as tube saturation current is reached, or the closer you get to the saturation current?
Increases
How can an atom be ionized?
The energy of the incoming electron must be greater than the binding energy of the electron it comes in contact with.
What types of interactions occur during production?
Brems and Characteristic
Of the two interactions produced during production, which one is more likely?
Brems
Which type of production interaction produces the most heat?
Brems
Describe Brems interactions:
Nucleus is positive, opposites attract. The negative electron being boiled off at the anode will change it’s path when it comes in contact with the K-shell of an atom. It travels around the nucleus and goes out with less energy than it entered. The energy difference is the Brems x-ray.
The (blank) the change in direction, the (blank) or (blank) the brems x-ray
Greater
Greater or Stronger
kVp primarily controls (blank) but as this goes up, so does…
Quantity, as it goes up-Quality increases as well
Higher kV does what to scatter?
Increases it
Higher kV does what to contrast?
Decreases it
Higher kV has what kind of scale of contrast?
Long scale contrast (more gray)
In order to produce Characteristic x-ray photons at the anode, the electron strength interacting with the K shell must be how strong, minimally?
69
Excitation occurs where and is what?
During production at the anode, and is where the atom is excited (vibrates) and produces heat but no interaction has occurred and no x-rays have been produced.
X-ray energy released from an outer shell electron filling the hole of an ionized k shell electron is the difference in the binding energy between them. This is what production?
Characteristic
An interaction between a negatively charged electron and a positive nucleus, in which the electron changes direction with reduced energy is what kind of production?
Brems
Where does the Brems X-ray energy come from?
When the negative electron comes in contact with the nucleus, the amount of change in direction that occurs with the electron determines the strength of the resulting brems.
The greater the change in direction an electron takes around the nucleus, the stronger or weaker the brems x-ray produced?
Stronger
–The greater the change in direction, the more energy was released-which IS the Brems–
Discrete Spectrum represents what?
Characteristic X-rays
Discrete spectrums depend on what?
The type of target
Atomic number of target materials changes the location of the discrete spectrum how?
Lower atomic numbers are further left on the horizontal line, and vice versa
Quantity is what on the discrete spectrum?
Amplitude (height)
To change amplitude in a discrete spectrum, you change what technical factor?
mAs (more mAs, the higher/taller the amplitude)
Continuous Spectrum represents what?
Brems photon X-rays
To change amplitude in a continuous spectrum you change what?
kVp
What does a combined emission spectrum graph show?
Both the Discrete and Continuous Spectrums
A Discrete Spectrum becomes relevant, when?
After x-ray photon strength becomes greater than 69(ish) when using a tungston target. This only changes when the atomic number changes.
Position in a discrete spectrum only changes when what changes?
Atomic number
An increase in filtration does what to the amplitude of curve on spectrum?
Reduces it. It filters out the lower energy photons.
Adding a filter and reducing the number of low energy photons exiting the tube does what to tube output of photons?
Increased quality. Photons leaving the tube have higher average energy.
When I increase filtration, what happens to my contrast?
The scale of contrast gets shorter. Fewer overall energies to work with.
What happens to amplitude on a Continuous and on a Discrete spectrum, when I add filtration?
It decreases.
As filtration increases, quality does what?
Increased
As filtration increases, quantity does what?
decreases
A change in atomic number of the target material results in a change in amplitude and shifting of which spectrum?
Discrete
An increase or decrease in mA or mAs, results in what change on the spectrum?
Amplitude, up or down
An increase is mAs does what to quantity of photons?
Increases
An increase in mAs does what to quality of photons?
Nothing, remains the same. Only kVp controls the quality/strength of the photons
A lower atomic number will shift the discrete spectrum in what direction?
Left
The higher the atomic number (Z), the (blank) the quality.
Higher (stronger the photon)
The higher the atomic number (Z), the (blank) the quantity.
Higher (more photons are produced)
130 kVp or 150 kVp which will produce the longest scale of contrast?
150 kVp
5:1 or 12:1 which grid ratio will give the longer scale of contrast?
5:1
the lowest grid ratio gives the longer scale of contrast.
As film screen speed/system speed increases, scale of contrast does what?
Decreases
Faster speeds produce short scale, more black and white
Slow speeds produce long scale, increase in contrast
What is the most common energy produced from kV operation?
1/3 the original energy
90 kV set, most common energy produced will be 30
Increasing kVp by 15% is equal to what?
What does this do to the photons?
- Doubling mAs
- Does not double the number of photons but it does increase the number of photons with sufficient energy to reach the IR
Decreasing kVp by 15% will do what to radiographic density?
Decrease it
If you increase kVp by 15% you do what to mAs?
And what is the resulting change in contrast?
Reduce by 50%
Longer scale of contrast
If you decrease kVp by 15%, what do you need to do to mAs?
And what is the resulting change in contrast?
Double mAs
Shorter scale of contrast
How would image density appear if you didn’t make the proper changes in mAs when increases or decreasing kVp?
Decrease in kVp with no change in mAs will have 1/2 the original density with a shorter scale of contrast
Increasing kVp with no change to mAs and the image will have double the original density with a longer scale of contrast
10 to the what?: Mega- M Kilo- K Milli- m Micro- Nano- n Angstroms- A (with circle on top)
M- 6th K- 3rd m- -3rd micro- -6th n- -9th A- -10th
X-ray emission:
Quantity is controlled by?
Quality is controlled by?
Number - mAs
Strength- kVp
What effect does mAs have on patient exposure?
Increases it
What effect does kVp have on patient exposure?
Decreases it
What kind of impact on image quality does kVp have?
Controls density
What kind of impact on image quality does mAs have?
Controls contrast
HVL is
Half Value Life
A quantitative numerical value.
A number for contrast (longer or shorter)
Beam intensity of 200 mR per hour with a HVL of 33 mm Al
What is new tube output?
100 mR
Compare the two:
A: 2.2 mL Al HVL
B: 4.1 mL Al HVL
A: Lower kV, shorter scale of contrast
B: Higher kV, longer scale of contrast
Why will a higher kVp produce a longer scale of contrast?
Higher kVp equals more scatter
Increased filtration removes (blank) photons from the beam…Fewer overall photon energies means a (blank) scale of contrast
Lower energy photons
Shorter scale of contrast
Inherent filtration is
Built into the tube or the person being imaged
Inherent AND added filtration does what to patient dose?
Decreases it
Photon production is
Characteristic/Brems
Photon Interactions are
Compton/Photoelectric
Production occurs where?
In the tube
Interactions occur where?
With matter outside the tube
Alpha and Beta are what types of interactions?
Particle
- Electric charge ON particle
- Mass of particle
Y-gamma ray, and X-ray are what types of interactions?
Photon
- Energy of photon (kVp)
- Type of matter (pt body tissue)
The higher the kVp, the higher or lower the probability of interactions?
And what kind of interactions?
And which is more likely of the two?
- Lower (more likely to pass through with no interaction to the IR)
- Compton and Photoelectric
- Compton more likely
Compton interactions produce what?
Scatter
Lots of gray
Photoelectric interactions produce what?
Absorption
White
Probability of X-ray interactions is dependent upon…
- Energy (i.e. wavelength)
- Type of matter
Low energy, long wavelength photons interactive with…
Whole atom
High energy, short wavelength photons interact with…
Nucleus
Types of Photon Interactions
- Transmitted through matter unchanged
- Change direction with no energy loss
- Change direction and lose energy
- Deposit all energy in the matter
A photon that changes direction with no energy loss is what kind of interaction?
Classical Scattering
- Low energy event
- Incidental photon (leaves matter with less energy)
A photon that changes direction and lose energy is what kind of interaction?
Compton Scattering
A photon that deposits all it’s energy in the matter is what kind of interaction?
Photoelectric (absorption)
Where would pair production occur?
In PET scanning
Radiation Therapy
When would photodisentegration occur?
AT 10 mega electron volts
Coherent or Elastic scattering are other names for what?
Classical Scattering
In Classical Scattering, a new photon travels in a different direction from the original photon but usually in what direction?
Forward
small scatter angle
Describe Photoelectric effect
An electron is ejected from it’s inner shell, and another electron moves in to take it’s place. That movement is what produces a Characteristic x-ray. (it is very weak and probably never getting out of the body)
What determines binding energies?
Anatomic number of the tissues
What are the results of the Photoelectric effect?
- Photon disappears
- Atom is ionized
- Characteristic photon(s) emitted
The probability of the photoelectric effect happening goes down sharply as photon energy does what?
Goes up
-photon is less likely to interact with the atom and pass through with no loss of energy
When is the likelihood of Photoelectric effect occurring at it’s maximum?
When kV and binding energy equal each other
As atomic number increases, the likelihood of photoelectric rapidly (blank)
Increases
-higher atomic number atoms absorb
Describe Compton Scattering
A photon ejects and electron from the OUTTER shell, the ejected (now moving) electron has kinetic energy. Ionizing an outer shell electron takes less energy that ionizing an inner shell electron. The photon gives up some of it’s energy and then continues on in a new direction, with less energy.
The more forward the scatter, the (blank) the energy kept by the incoming photon. (less angulation)
Higher
As the angle increases, the photon gives up (blank) energy.
More
High energy photons scatter with what type of angle?
Smaller
They’re strong and give up little energy.
High energy photons are more likely to scatter in what direction?
So image density (blank)
- Forward
- Increases
Low energy photons are more likely to do what?
Backscatter
They’re weaker and give up most of their energy
Compton scattering contributes to what?
- Personnel and patient exposure
- Film fog (decreased contrast)
With higher kV which type of interaction is produced more? Compton or Photoelectric?
Compton
Probability of Compton interactions increases as density of matter (blank)
Increases
Atomic number does not effect compton scattering likelihood
Compton scattering (blank) in matter containing abundant hydrogen
Increases
Compton likelihood (blank) as photon energy increases
Decreases
As energy increases both PE and Compton (blank)
Decrease
PE interactions (blank) more rapidly than Compton
Decrease
Describe Pair Production
When a high energy photon equal to or greater than 1.02 mev’s enters the nucleus of an atom and the nucleus completely disappears becoming 2 electrons, one positive and one negative.
The photon ceases to exist.
Scatter contributes what to an image?
Density, which is associated with a long scale of contrast.
How does pair production happen?
When an x-ray photon strength is equal to or greater than 1.02 mega electron volts comes in contact with the nucleus, the photon disappears and two electrons are created, one positive and one negative.
Describe photodisentigration…
The nucleus is excited and instantly emits a nucleon. The photon is absorbed by the nucleus. This occurs at 10 mev
How do you calculate heat units? (HU)
Single phase: mA x time x kVp 3 phase 6 pulse: mA x time x kVp x 1.35 3 phase 12 pulse: mA x time x kVp x 1.41
