Unit 3: X-ray Production and Anode Heel Flashcards
What is the negatively charged side of the tube?
Cathode
During exposure, the Cathode has a what type of potential?
Large Negative Potential
What material is the focusing cup made of?
Nickel
(has a high heat capacity)
What does the focusing cup do?
Focuses the Space Cloud
What kind of charge does the focusing cup possess?
Low negative charge
Why are the tungsten filaments coated in thorium?
Thorium allows for a more efficient thermionic emission process by burning off 2% more electrons.
What is thermionic emission?
The process of burning off electrons
What forms the focused electron cloud (space cloud)?
Thermionic emission
What type of energy does the space cloud possess?
Potential Energy
What is potential energy?
- Energy at rest.
- Ability to do work by virtue of position.
What is kinetic energy?
- Energy in motion
- Possessed by all matter in motion
Incident electrons moving toward the anode possess what type of energy?
Kinetic Energy
When the electrons hit the heavy metal atoms of the target, what happens to their kinetic energy?
Their kinetic energy is transferred to the target atoms.
What percentage of kinetic energy is turned into heat?
99.8%
What percentage of kinetic energy is turned into useful x-rays?
Less than 1%
What is the distance between the target and the filament?
1cm
What is the measure of the maximum electrical potential across an x-ray tube?
kVp
Potential Difference
Electromotive Force
Voltage
Different terms for kVp
When is kVp applied to the tube?
When the exposure button is pressed.
Does kVp control the temperature of the filament?
No
Does kVp control how many electrons are in the focusing cup?
No
Does kVp control how many electrons cross the tube?
No
kVp does not create a larger x-ray beam because more electrons are burned off.
kVp does not create a larger x-ray beam because more electrons are burned off.
When the exposure button is pressed, how does this affect the anode and cathode?
The anode becomes positively charged and the cathode becomes negatively charged.
Most radiographs use what range of kVp techniques?
50-120 kVp
How many volts is 1 kVp?
1,000 volts = 1 kVp
When kVp is increased, more electrons become attracted to the anode, which _____ the quantity of x-rays in the beam.
Increases
What increases the probability that all available electrons in the space charge will be attracted to the anode?
Increasing kVp
Increasing the kVp, results in the electrons possessing a greater kinetic energy when traveling from the cathode to the anode, this will make for a higher _______ beam.
Quality (penetrating)
What is it called when all possible electrons are attracted to the target?
Saturation Current
Does increasing kVp make x-ray photon production more efficient or inefficient?
More efficient
Does tube current have an effect on the efficiency of x-ray photon production?
No
mAs controls ____
Quantity
What is selected by the tech as the maximum voltage of a photon beam during an x-ray exposure?
(kVp vs. keV)
kVp
X-ray tube voltage describes ___?
(kVp vs. keV)
kVp
X-ray tube potential between the cathode to the anode describes ___?
(kVp vs. keV)
kVp
What does the unit eV describe?
The kinetic energy of the electrons in the x-ray tube and the photons produced at the target.
What determines the top keV value of the incident electron or x-ray photon produced?
kVp
What describes how fast an object is traveling?
Velocity
How fast are the electrons traveling from the cathode to the anode?
at half the speed of light
Tube voltage is expressed in ___?
kVp
Tube current is expressed in __?
mA
What is the tube current determined by?
The number of electrons emitted by the filament during thermionic emission.
Apply kVp (potential difference) to the x-ray tube converts the ______ energy of the electron cloud into ______ energy of the electrons in motion.
Apply kVp (potential difference) to the x-ray tube converts the POTENTIAL energy of the electron cloud into KINETIC energy of the electrons in motion.
X-ray photon production follows the acceleration of electrons.
X-ray photon production follows the acceleration of electrons.
When an electron is slowed down as it interacts with the anode, describes which type of electron target interaction?
Electron Deceleration
What are the two types of electron target interactions?
Electron Deceleration
Electron Ionization
With electron deceleration, when is the x-ray photon produced?
When the electron is slowed down
What type of x-rays (Bremsstrahlung or Characteristic) are produced with electron deceleration?
Bremsstrahlung X-rays
When an incident electron ionizes an atom of the target material, which type of electron target interaction is this?
Electron Ionization
What term means to remove an electron from an atom of tungsten?
Ionize
With electron ionization, when is the x-ray photon produced?
When the cascading effect takes place.
What type of x-rays (Bremsstrahlung or Characteristic) are produced with electron ionization?
Characteristic
What does the term Bremsstrahlung mean?
“Slowed Down Radiation”
or
“Braking Radiation”
When are Bremsstrahlung x-rays produced?
When the high-speed electrons incident from the cathode interact with the NUCLEUS of a tungsten atom.
Bremsstrahlung x-rays vary from low energy (keV) x-rays to the peak energy (keV) of the kVp selected on the control panel.
Bremsstrahlung x-rays vary from low energy (keV) x-rays to the peak energy (keV) of the kVp selected on the control panel.
What percentage of the primary beam is made up of Bremsstrahlung x-rays?
90%
What charge does the nucleus of a tungsten atom possess?
Positive charge
A car turns a corner at a high speed and veers off of its original trajectory. A portion of the energy that was contained in the kinetic energy of the tire is transferred into heat, making a “skid mark”. The tire retains the rest of the energy as it turns the corner.
Referring to this example, the original kinetic energy of the tire is equivalent to___?
Original kinetic energy of the incident electron
A car turns a corner at a high speed and veers off of its original trajectory. A portion of the energy that was contained in the kinetic energy of the tire is transferred into heat, making a “skid mark”. The tire retains the rest of the energy as it turns the corner.
Referring to this example, the energy of the skid mark is equivalent to __?
The energy spent to create an x-ray photon from the electron being forced to slow down.
A car turns a corner at a high speed and veers off of its original trajectory. A portion of the energy that was contained in the kinetic energy of the tire is transferred into heat, making a “skid mark”. The tire retains the rest of the energy as it turns the corner.
Referring to this example, the final kinetic energy of the tire after turning is equivalent to ____?
The final kinetic energy of the incident electron after turning towards the nucleus.
Law of Conservation of Energy (Brems)
Original keV of the incident electron = keV of Bremsstrahlung x-ray photon + keV of the electron after nucleus influence
A sharper turn around the nucleus results in a higher or lower energy photon?
Higher
If kVp increases, Quality and Penetration ______
Increase
Two variables determining x-ray keV
Proximity to nucleus
Original kVp setting
In the diagnostic range, which type of x-rays are majority of the primary beam?
Bremsstrahlung
Which type of x-ray production is responsible for the polyenergetic nature of the x-ray beam?
Bremsstrahlung
Do very low energy (keV) x-rays contribute anything to the image?
No, just the patient’s dose.
How are low energy Bremsstrahlung x-rays that don’t contribute to diagnostic radiographs dealt with?
Filtration
Filtration creates a more _______ beam.
Monoenergetic
If filtration is increased, the average quality of the x-ray beam is increased, and intensity is ______.
Decreased
All atoms are comprised of a nucleus surrounded by shells that contains _____.
Electrons
What does the nucleus contain?
The atom’s protons and neutrons
What determines the atomic number of the atom?
The number of protons
An atom contains the same number of protons and electrons until it loses or gains an electron. What process is this?
Atom Ionization
An incident electron must contain at least __ keV in order to collide with and remove a K-shell electron from a tungsten atom.
69 keV
When the cathode electron ionizes a target atom by removing a K-shell electron, a temporary electron void is produced at the K-shell. The outermost shell then falls into the void of the K-Shell. What is this called?
Cascading Effect
The transition of an orbital electron from an outer shell to an inner shell is accompanied by the emission of ______
an X-ray
The outer shell electron drops into the inner shell electron to fill the void left by ionization, results in a _______ photon.
Characteristic photon
K-shell keV value
69 keV
L-shell keV value
12 keV
The energy of x-rays created by the K-shell will always be _____
57 keV
What makes up the discrete portion of the beam?
Characteristic X-rays
What percentage of the primary useful beam is Characteristic X-rays?
10%
At 70 kVp, the percentage of characteristic x-rays in the primary beam is ___
10%
At 100 kVp, the percentage of characteristic x-rays in the primary beam will increase to ___
15%
How are Characteristic x-rays better than Bremsstrahlung x-rays?
They aren’t
Which type of x-ray production is responsible for the monoenergetic energies of the x-ray beam?
Characteristic X-rays
How would you move the discrete portion (“the line”) in the beam?
Changing the material.
Not by changing kVp.
Which side of the tube has a greater number of photons?
Cathode
A radiographic phenomenon affecting the intensity of the x-ray beam.
Anode Heel Effect
Due to the angle of the anode, a greater number of incident x-ray photons will be produced at _____
The cathode side of the tube
Three variables affecting Anode Heel Effect
1) SID
2)Anode Target Angle
3) Image Field Size
What kind of relationship do SID and Anode Heel Effect have?
Indirect
What kind of relationship do Field Size and Anode Heel Effect have?
Direct
What kind of relationship do Anode Target Angle and Anode Heel Effect have?
Indirect
A smaller angle results in a _______ image.
Sharper
“FAT-CAT”
The thicker part goes under the cathode side of the tube.
Examples of FAT-CAT
Femur
Lower Leg
Humerus
T-Spine
L-Spine
Beam Intensity
Quantity of x-ray photons within the beam
Exit Beam
When the beam exits the pt. and hits the IR
