xray tube/ beam intensity

Added Filtration: required by law

• How it works
  

  • reduced by [...] 

  • Absorber placed in path of exiting X-Rays

  • Aluminum is an excellent filter for low energy radiation 

photoelectric reactions

Added Filtration: required by law

• How it works
  

  • reduced by photoelectric reactions 

  • Absorber placed in path of exiting X-Rays

  • Aluminum is an excellent filter for [high or low] energy radiation 

low

Added Filtration: required by law

• Measured in actual or equivalent aluminum thickness

• 50 to 70 kVp range requires [...] mm total Al filtration
  

  • [...] added 

• 1.5

• 0.5

Anode Heel effect: x-ray beam intensity is not uniform  

• Heel effect [increases or decreases] with decreasing anode angels

increases

Anode Heel effect: x-ray beam intensity is not uniform  

• Higher intensity is on the cathode side
  

  • Consequently, [thick or thin] body parts should be positioned toward the cathode 

thicker

Anode Tungsten Target

• [...]: target area bombarded by electrons

• [...]: area/shape of beam projected onto the patient 
  

  • Angling the anode target creates an effective focal spots that is much smaller than the focal spot (thus producing sharper image

• Focal Spot

• Effective Focal Spot

Binding Energy Review

• Bound particles always have a [positive or negative] potential energy

• To free electron from an atom, energy must be raised to zero or a positive value 

negative

Bremsstrahlung Radiation (“Braking” Radiation)

• Angle of deflection is random & electrons can penetrate through many anode layers before it is forced to change direction

• As a result, [what?]

• exiting photons have many different energy values (they’re polyenergetic)

Bremsstrahlung Radiation (“Braking” Radiation)

• Each deflection yields a [...] of radiation

photon

Cathodes

• Current applied to [...]
  

  • Attains a very high temperature (this is why tungsten is chosen bc it has a very high melting point so it can take the heat)

  • Units in Amps (A) 

tungsten filament

Cathodes

• Current applied to tungsten filament
  

  • Attains a very high temperature (this is why tungsten is chosen bc it has a very high melting point so it can take the heat)

  • Units in [...] 

• Amps (A) 

Cathodes

• Filament Circuit
  

  • Voltage across filament is [...]

  • Current across filament is [...]

    • (higher current than the X-Ray tube, which has low current in mA & high voltage)

  • Power dissipated is [...]

• 10 V

• 4A

• 40W

Cathodes

• [...] surrounds the filament coil
  

  • Function: aiming device

    • As the negative electrons are emitted from the tungsten coil, they’re repelled by negative EN of the focusing cup, which allows the beam to narrow and target the positive anode target 

Focusing cup

Cathodes

• Focusing cup surrounds the filament coil
  

  • Function: [...]

    • As the negative electrons are emitted from the tungsten coil, they’re repelled by negative EN of the focusing cup, which allows the beam to narrow and target the positive anode target 

aiming device

Cathodes

• Focusing cup surrounds the filament coil
  

  • Function: aiming device

    • [but how?] 

• As the negative electrons are emitted from the tungsten coil, they’re repelled by negative EN of the focusing cup, which allows the beam to narrow and target the positive anode target 

Cathodes

• [...]
  

  • High resistance in the filament causes temperature to rise > 2200 deg C

  • Electrons “boil-off” or ionization from the tremendous heat and form a negatively charged electron cloud that will be attracted to the positive anode 

• Thermionic Emission

Cathodes

• Thermionic Emission
  

  • High resistance in the filament causes temperature to rise > 2200 deg C

  • Electrons “boil-off” or ionization from the tremendous heat and form a [...] that will be attracted to the positive anode 

negatively charged electron cloud

Characteristic Radiation

• As we [do what], we increase the probability that a K shell electron will be knocked out so that 10 to 28% of x-rays are due to characteristic radiation 

increase kVP

Characteristic Radiation

• Ionized tungsten anode atom returns to its normal energy state by [...]
  

  • Therefore, it [is or is not] polyenergetic 

• emitting radiation in the x-ray wavelength

• is NOT

Filtration

• Filters out [what?]

• majority of soft radiation (long wavelength, low energy)

This hardens the beam (bc soft ones have been eliminated

Filtration

• Just 1 mm of aluminum cuts exposure to skin by [...]

half! 

Filtration

• Measured in [what unit] of actual or equivalent aluminum thickness 

millimeters

his hardens the beam (bc soft ones have been eliminated

Inherent vs Added

• Total Filtration = [...] + [...] 

Added + Inherent 

Inherent: total filtering in every x-ray tube head

• About [...] to [...] mm Al Equivalent

• Results when X-Rays pass through
  

  • Glass envelope

  • Insulating oil surrounding tube

  • Window (bakelite, etc.) 

0.9 to 1.0

Inherent: total filtering in every x-ray tube head

• About 0.9 to 1.0 mm Al Equivalent

• Results when X-Rays pass through
  

  • [...]

  • [...]

  • [...] 

• Glass envelope

• Insulating oil surrounding tube

• Window (bakelite, etc.) 

Normal Binding shell energies for Tungsten (energetic electron has to equal or be greater than the BE in order for this to happen)

• K shell – [...] keV

• L Shell – [...] keV

• M Shell – [...] keV 

• K shell – 70 keV

• L Shell – 11 keV

• M Shell – 2 keV 

Rotating vs Stationary Design of Anode

• Focal spot is the [same or different?] size in both

• Rotating Design Benefits
  

  • Increased surface area & better at dissipating heat

    • Motor spins anode to high speed to dissipate heat 

same

Rotating vs Stationary Design of Anode

• Focal spot is the same size in both

• Rotating Design Benefits
  

  • [...] & [...]

    • Motor spins anode to high speed to dissipate heat 

• Increased surface area & better at dissipating heat

Three basic Anode Interactions

• 99% – [...]  

• 0.9% – [...]

• 0.1% – [...] 

• 99% – Infrared Radiation  

• 0.9% – Bremsstrahlung Radiation

• 0.1% – Characteristic Radiation

Two benefits of Tungsten Target

• [...]

• [...] 

• High melting point (3370 deg C)

• High atomic number (Z = 74) 

High atomic number is important because electrons are in its K shell has a high BE so when releases a lot of energy when the electrons are pried away 

Typical Polyenergetic Bremsstrahlung Curve

• Area under the curve is [...]

• Peaks at 1/3 of the total kVp that the x-ray machine is set to 

• Spikes on the curve is because of characteristic radiation 

the number of photons

Typical Polyenergetic Bremsstrahlung Curve

• Area under the curve is the number of photons

• Peaks at [...] that the x-ray machine is set to 

• Spikes on the curve is because of characteristic radiation 

1/3 of the total kVp

Typical Polyenergetic Bremsstrahlung Curve

• Area under the curve is the number of photons

• Peaks at 1/3 of the total kVp that the x-ray machine is set to 

• Spikes on the curve is because of [...]

• characteristic radiation 

Wedge filter – great for the foot

• In the foot, the thick part of the wedge should be over the [...] and the thin part of the wedge should be over the [...] 

• toes (which are thin)

• dense midfoot 

Wedge filter – great for the foot

• Not used all the time because [...] 

you’d have to teach every technician (steep learning curve) 

Wedge filter – great for the foot

• Thin part of the patient is under the [thin or thick] part of the wedge  

thick

(this way, thin part of the patient doesn’t get the brunt of the radiation)

Why have wide beam at all then, if narrow beam produces sharper images?

• [...]

• Also, [...] 

• Narrow beams only cover a small area so can’t x-ray large areas like the abdomen

• the Heel Effect 

[...]: x-ray beam intensity is not uniform  

• X-ray intensity is 100% in the center, called the central ray

• Towards the anode, x-ray intensity decreases

• Towards the cathode, x-ray intensity increases

Anode Heel effect

Anode Heel effect: x-ray beam intensity is not uniform  

• X-ray intensity is 100% in the [...], called the [...]

• Towards the anode, x-ray intensity decreases

• Towards the cathode, x-ray intensity increases

• center

• central ray

Anode Heel effect: x-ray beam intensity is not uniform  

• X-ray intensity is 100% in the center, called the central ray

• Towards the anode, x-ray intensity [increase or decrease]

• Towards the cathode, x-ray intensity [increase or decrease]

• decreases

• increase

• [...], tube current is space charge limited

• [...], all electrons are pulled away from the filament & tube current is maximized
  

  • Tube current is now largely controlled by filament heating 

• At low kVp (below 40 kVp)

• At saturation voltage (40 kVp)

• At low kVp (below 40 kVp), tube current is space charge limited

• At saturation voltage (40 kVp), all electrons are pulled away from the filament & tube current is maximized
  

  • Tube current is now largely controlled by [...] 

• filament heating 

[...]

• Happens when a very high-energy electron gets really close to the nucleus (through the K Layer) and is diverted by nucleus
  

  • Change in direction causes energy to be lost. This energy becomes a photon (braking effect)

  • There is NO collision, simply a change of direction due to opposing nuclear forces 

Bremsstrahlung Radiation (“Braking” Radiation)

[...]

• Electrons bombarding the target is able to knock out one of the inner orbital electrons
  

  • Possible because incoming electron energy is equal to or greater than the atomic shell binding energy 

Characteristic Radiation

Characteristic Radiation

• Electrons bombarding the target is able to knock out one of the inner orbital electrons
  

  • Possible because [of what?] 

• incoming electron energy is equal to or greater than the atomic shell binding energy 

[...]: compensate for part density variation   

• Wedge filter – great for the foot

• Trough/bilateral wedge filter – great for the chest 

Compensating Filters

[...]

• Combined layer of Al (Z=13) & Cu (Z=29)
  

  • Decreases filter thickness for very high energy beams

  • Copper faces X-Ray beam 

Compound Filter

Compound Filter

• Combined layer of [...] & [...]
  

  • Decreases filter thickness for very high energy beams

  • Copper faces X-Ray beam 

Al (Z=13) & Cu (Z=29)

Compound Filter

• Combined layer of Al (Z=13) & Cu (Z=29)
  

  • [increases or decrease] filter thickness for very high energy beams

  • Copper faces X-Ray beam 

Decreases

Compound Filter

• Combined layer of Al (Z=13) & Cu (Z=29)
  

  • Decreases filter thickness for very high energy beams

  • [...] faces X-Ray beam 

Copper

[...] principle: anode is angled to decrease focal spot size

• Smaller focal spot = sharper images

• shallow angles = sharper images 

Line-Focus

Line-Focus principle: anode is angled to [increase or decrease] focal spot size

• Smaller focal spot = sharper images

• shallow angles = sharper images 

decrease

Line-Focus principle: anode is angled to decrease focal spot size

• [...] = sharper images

• [...] = sharper images 

• Smaller focal spot

• shallow angles

[...]

• negative cloud of electrons emitted from filaments which repel subsequent negative electrons from the filament

• limiting factor 

Space charge

[...] filter – great for the chest

• Central thin part is positioned over the mediastinum (more dense)

Trough/bilateral wedge

Trough/bilateral wedge filter – great for the chest

• Central thin part is positioned over the [...]

mediastinum (more dense)

[...]: flow of electrons across vacuum gap (from filament) to anode completes the circuit

• units is mA (because high voltage requires low current) 

Tube current

Tube current: flow of electrons across vacuum gap (from filament) to anode completes the circuit

• [what are the units?] 

• units is mA (because high voltage requires low current) 

Dual Focal Spot Anode

• Has a rotating anode that has two different angels
  

  • 12 degrees = [why?]

  • 6 degrees = [why?]

Dual Focal Spot Cathode

• Has two filaments with more coils for the 12 degree wider field option  

• wide field for larger areas

• narrow field for smaller areas

[...]

• Has a rotating anode that has two different angels
  

  • 12 degrees = wide field for larger areas

  • 6 degrees = narrow field for smaller areas

[...]

• Has two filaments with more coils for the 12 degree wider field option  

• Dual Focal Spot Anode

• Dual Focal Spot Cathode

Dual Focal Spot Anode

• Has a rotating anode that has two different angels
  

  • 12 degrees = wide field for larger areas

  • 6 degrees = narrow field for smaller areas

Dual Focal Spot Cathode

• Has two filaments with more coils for [...]  

the 12 degree wider field option