x ray beam

(Milliamperage)(time) --> mAs

• mA is a user selectable control (sometimes it can be constant)
  

  • if constant, [what's the problem?]

patient motion is a risk that it will blur the image

(Milliamperage)(time) --> mAs

• Milliamperage is [...]

• mAs is [...]

• quantity of photons

• the total number of photons/radiations during a specific time of exposure 

15% change in Kilovoltage

• Quality of photonic energy is [...]

• Quantity of photons is also [...]

• increased (peak is further down)

• increased (increased area under the curve) 

15% Rule

• In order to maintain image density, an increase of kVp by 15% should be accompanied by a [...]% [increase or decrease] of mAs

50% decrease

Inc. in 15% of kVp = dec. in 50% of mAs

4 basic factors affecting quantity of x-ray beam photons

1. [...]

2. [...]

3. [...]

4. [...] 

1. (Milliamperage)(time) --> mAs

2. Kilovoltage (kVp)

3. Distance

4. Filtration 

Absorbed Dose (D)

• Conversion
  

  • One gray = [...] Joule (J) of energy deposited per kilogram

  • One rad = [...] ergs of energy deposited per gram

  • 1 Gy = [...] Rads

  • 1 rad = [...] mGy 

• 1

• 100

• 100

• 10

Absorbed Dose (D)

• D = [...]

• Units:
  

  • SI system – Gray (Gy)

  • Non-SI – Rads 

E/M

Absorbed Dose (D)

• D = E/M

• Units:
  

  • SI system – [...]

  • Non-SI – [...] 

• Gray (Gy)

• Rads

As a polyenergetic beam goes through objects, how does it impact the HVL? 

• [...] 

• Since the beam is getting more energetic, HVL increases after each obstacle because the thickness needed to decrease beam intensity has to go up when beam intensity is increasing 

Basic interactions with matter

• Insignificant
  

  • [...]

  • [...]

  • [...]

• Significant
  

  • Photoelectric absorption

  • Compton Scatter 

• Coherent scatter (5%)

• Pair Production

• Photodisintegration

Basic interactions with matter

• Insignificant
  

  • Coherent scatter (5%)

  • Pair Production

  • Photodisintegration

• Significant
  

  • [...]

  • [...] 

• Photoelectric absorption

• Compton Scatter 

Basics of Attenuation

• Factors increasing attenuation
  

  • [...]

  • [...]

  • [...] 

• Density

• Atomic Number (Z)

• Electrons per gram of tissue 

• Density = denser objects will decrease intensity and therefore increase attenuation

• Atomic Number (Z) = higher atomic numbers present more obstacles (more electrons, protons, etc.) and therefore increase attenuation

• Electrons per gram of tissue 

Compton Scatter Angle of deflection

• Greater the angle, the [more or less] energy is lost 

more

Does an x-ray beam have more or less energy after it goes through a wall?

• [...]

• An x-ray beam that makes it through a wall has more energy because only the strong beams make it through the wall

Does changing the kilovoltage affect the quality? 

• [...]

• [...]

• yes, overall effect on film blackening is approximately equal to the fourth power

• peak is moved to the right a little 

Does doubling the Milliamperage change energy distribution?

• [...]

• does NOT change energy distribution (peak is at the same spot) 

Dose Equivalent (H)

• H = [...] x [...]

• absorbed dose x quality factor

H = D x QF 

Dose Equivalent (H)

• Quality factor – derived from LET values
  

  • QF of x-rays, Gamma, electrons, beta particles is [...]

    • So, 1 rad = [...] rem in diagnostic radiology

  • QF may be as high as 20 for alpha particles/heavy nuclei 

• 1.0

• 1

Dose Equivalent (H)

• Units for Dose Equivalent (H)
  

  • SI system – [...]

  • Non- SI – [...]

  • Conversion rates

    • 1 Sv = 100 rem

    • 1 rem = 10 mSv

• Sievert (Sv)

• Rem (rad. Equiv. man)

Dose Equivalent (H)

• Units for Dose Equivalent (H)
  

  • SI system – Sievert (Sv)

  • Non- SI – Rem (rad. Equiv. man)

  • Conversion rates

    • 1 Sv = [...] rem

    • 1 rem = [...] mSv

• 100

• 10

Doubling Filter Thickness

• [increase or decrease] quality

• [increase or decrease] quantity

• Increases

• Decreases

Doubling Filter Thickness

• [how does it affect quality?]

• [how does it affect quantity?]

• Rightward shift of the peak which means there is a higher quality of energy produced (bc lower energy x-rays are filtered out)

• Area under the curve decreases because the quantity of the energy decrease (bc some of the photons are obviously being eliminated)

Effect of Milliamperage Doubling

• [what happens to quality?]

• [what happens to quantity?]

• Quality of photonic energy is NOT affected (peak is at the same spot)

• Quantity of photons double (area under the curve is doubled)

Effective Atomic Numbers of Various Materials Important to Diagnostic Radiology

• Contrast Agents = [...], [...], [...]
  

  • Helps to have clearer images

Air, Iodine, Barium

Effective Atomic Numbers of Various Materials Important to Diagnostic Radiology

• Human tissue (fat, muscle, lung, bone)
  

  • [what has the highest effective atomic number]

  • Overall low effective atomic numbers

    • Indicates a low BE that is so low that none of the characteristic radiation will exit the body but will rather be absorbed 

• Bone has the highest effective atomic number

Effective Atomic Numbers of Various Materials Important to Diagnostic Radiology

• Human tissue (fat, muscle, lung, bone)
  

  • Bone has the highest effective atomic number

  • Overall [high or low] effective atomic numbers

    • [what does this indicate about absorption?] 

• low

• Indicates a low BE that is so low that none of the characteristic radiation will exit the body but will rather be absorbed 

Factors decreasing attenuation

• [...]

• Kilovoltage

increasing kVp will just increase punching power so it will just break through matter like hulk 

How are beam intensity and mA related?

• [...] 

• Beam intensity and mAs are directly proportional
  

  • Doubling mAs will double the number of emitted x-rays 

HVL [increases or decreases] with increasing filtration

increases

High-Value Layer: thickness of an aluminum absorber that is required to reduce beam intensity by 50% 

HVL increases with [increased or decreased] filtration

increasing

High-Value Layer: thickness of an aluminum absorber that is required to reduce beam intensity by 50% 

If you want to use the barium as the contrast agent, what should the x-ray kVp be set as? 

• [...] 

• Barium = 37.4 K-shell binding energy. So, set the x-ray machine to about 112 so that the peak will be at about 37.4 (1/3 of the total) and therefore allowing a photoelectric reaction 

Intensity (exposure) = product of number of photons & their average energy

• Intensity = ([...])([...])

• Unit of measurement = Roentgen (R)
  

  • 1 R = amount of radiation to liberate 2.58e-4 Coulombs per kg of air

(quantity)(quality)

Intensity (exposure) = product of number of photons & their average energy

• Intensity = (quantity)(quality)

• Unit of measurement = Roentgen (R)
  

  • 1 R = [...]

• amount of radiation to liberate 2.58e-4 Coulombs per kg of air

Inverse Square Law

• Doubling distance from x-ray source [increases or decreases] intensity by a factor of [...] 

• decreases

• 4

Radiation intensity varies inversely with the distance squared from the source

SAME number of photons, just diluted with distance

Is it safer to increase the distance between you and the x-ray beam or is lead better? 

• [...]

distance

Linear Energy Transfer (LET)

• High LET has [high or low] penetration but [high or low] absorption

• Low LET has [high or low] penetration but [high or low] absorption 

• Low, High

• High, low

Linear Energy Transfer (LET)

• [directly or inversely] related to particle KE 

Inversely

Linear Energy Transfer (LET)

• [high or low] LET = photons electrons, gamma, & x-rays

• [high or low] LET = neutrons, protons, and alpha particles 

• low

• high

Lower HVL means the beam has [...]

too many low-beam photons

High-Value Layer: thickness of an aluminum absorber that is required to reduce beam intensity by 50% 

HVL increases with filtration, so a low HVL doesn't have much filtration which means a lot of low energy photon gets through 

Monoenergetic Attenuation

• [how does a monoenergetic beam respond to more HVL layers?]

With more HVL layers, a monoenergetic beam decreases in quantity (number of photons)

With more HVL layers, a monoenergetic beam decreases in quantity (number of photons)

nearly the same 

PE vs Compton Scatter Probabilities

• Relative probabilities
  

  • Almost everything we see in imaging is due to [PE or Compton] because they’re what is present in high x-ray energies

  • Safety factor: x-ray machine with high kVp potential usually require lead placed into the wall as a precaution, because you don’t know where the electrons will scatter

Compton scatters

PE vs Compton Scatter Probabilities

• Relative probabilities
  

  • Almost everything we see in imaging is due to Compton scatters because they’re what is present in high x-ray energies

  • Safety factor: x-ray machine with high kVp potential usually require lead placed into the wall as a precaution, because [...]

• you don’t know where the electrons will scatter

PE vs Compton Scatter Probabilities

• With water
  

  • Photoelectric reactions increase with [increase or decreased] kVp

  • Compton Scatter reactions increase with [increase or decreased] kVp 

  • At 26 kVp, 50% of interactions are photoelectric and Compton scatter 

• decreased

• increased

Meaning at low kVp, our bodies are significantly absorbing radiation

PE vs Compton Scatter Probabilities

• With water
  

  • Photoelectric reactions increase with decreased kVp

  • Compton Scatter reactions increase with increased kVp 

  • At [...] kVp, 50% of interactions are photoelectric and Compton scatter 

26

Meaning at low kVp, our bodies are significantly absorbing radiation

PE vs Compton Scatter Probabilities

• With bone
  

  • Photoelectric reactions increase with [increased or decreased] kVp

  • Compton Scatter reactions increase with [increased or decreased] kVp

  • At 45 kVp, 50% of interactions are photelectric and Compton scatter

• decreased

• increased

PE vs Compton Scatter Probabilities

• With bone
  

  • Photoelectric reactions increase with decreased kVp

  • Compton Scatter reactions increase with increased kVp

  • At [...] kVp, 50% of interactions are photelectric and Compton scatter

45

Photoelectric Reaction

• ([...]) – ([...]) = KE of the electron that escapes

(Energy of the incident photon) – (electron BE)

Photoelectric Reaction

• 3 basic products:
  

  1. [...]

  2. [...]

  3. [...] 

• Photoelectron

• Characteristic radiation

• Positive ion 

Photoelectric Reaction

• Photon is absorbed
  

  • [describe the process.]

• Atom resolves energy imbalance by dropping an outer orbital electron 

• incident photon interacts with an inner orbital, K or L, electron with an energy higher than the electron’s binding energy, which causes the electron to be ejected & the photon to be absorbed

Photoelectric Reaction

• Photon is absorbed
  

  • incident photon interacts with an inner orbital, K or L, electron with an energy higher than the electron’s binding energy, which causes the electron to be ejected & the photon to be absorbed

• Atom resolves energy imbalance by [...] 

• dropping an outer orbital electron 

Photoelectric Reaction

• Similar to spike of characteristic spike except for some key differences:
  

  • Atomic number is much [higher or lower] than Tungsten

  • Photon is coming in and knocking an electron out of its orbital instead of another electron coming in

  • Much [higher or lower] energy 

• lower

• lower

Photoelectric Reaction

• Similar to spike of characteristic spike except for some key differences:
  

  • Atomic number is much lower than Tungsten

  • [what knocks the electron out of its orbital in a photoelectric reaction]

  • Much lower energy 

• Photon is coming in and knocking an electron out of its orbital instead of another electron coming in

Photoelectric Reaction

• Yields [strong or weak] characteristic radiation in biologic system 
  

  • Much lower energy so it can’t travel for long before it is completely absorbed (if it’s a human, it won’t leave the body) 

weak

Photoelectric Reaction

• Yields weak characteristic radiation in biologic system 
  

  • [what is the significance of this?] 

• Much lower energy so it can’t travel for long before it is completely absorbed (if it’s a human, it won’t leave the body) 

Polyenergetic Attenuation

• When going through more obstacles, a polyenergetic beam [...]

decreases in quantity and increases in quality

Polyenergetic beam becomes [...] after 3 to 4 HVL’s 

functionally monoenergetic

Radiation intensity varies inversely with the distance squared from the source

• Due to [...]

the X-Ray beam divergence

• shifting the peak indicates a change in [...] 

• changing the area under the curve indicates a change in [...] 

• quality 

• quantity

the tighter electrons are bound in orbit, photoelectric reaction is more likely

• Photoelectric reaction likelihood = [...]

• (atomic number)³

Higher atomic number = higher BE = tighter the electrons are bound

so higher the atomic number, the more likely a PE reaction would occur

the tighter electrons are bound in orbit, photoelectric reaction is [more or less] likely 

more

P.E. = Z³

To get through a thicker layer, you can either increase kVp or increase mAs. What is safer?

• [...] 

• kVp’s is actually saver
  

  • more radiation is deposited by low kVp 

Two basic factors affecting quality of x-ray beam photons (shifts the curve)

1. [...]

2. [...]

1. Kilovoltage (kVp)

2. Filtration

But the only one that can be changed is the kVp because filtration is required by law

Vocabulary

• [...]: photons pass through unaffected
  

  • Matter is NOT ionized

• [...]: transfer energy to absorbing medium
  

  • Matter IS ionized

• [...]: photons change energy and possibly lose energy  
  

  • Matter MAY OR MAY NOT be ionized 

• Penetrate

• Absorbed

• Scattered

Vocabulary

• Penetrate: photons pass through unaffected
  

  • [Is matter ionized?]

• Absorbed: transfer energy to absorbing medium
  

  • [Is matter ionized?]

• Scattered: photons change energy and possibly lose energy  
  

  • [Is matter ionized?] 

• Matter is NOT ionized

• Matter IS ionized

• Matter MAY OR MAY NOT be ionized 

What does the term "beam hardening" mean? 

• [...] 

increaseing effective beam energy through preferential loss of lower (softer) energy photons 

What has the lowest HVL & what does that indicate? 

• [...]

• Lead is the most efficient at cutting down x-ray beam so it is the best shield
  

  • A much thinner lead filter can do the same work as thicker cm. of muscle or bone

High-Value Layer: thickness of an aluminum absorber that is required to reduce beam intensity by 50% 

What is the ONLY interaction between x-ray and matter that does not cause ionization? 

• [...]

• Coherent Scatter

Low energy photons are simply absorbed & causes a vibration of the electron cloud before it goes back to the same energy 

What is the relationship between beam intensity and kVp? 

• [...]

• Beam intensity is directly proportional to kVp2
  

  • Defines the quantitative effect

  • It is exponential!!!

    • Doubling the kVp increases beam intensity fourfold & vice versa

[...]

• Measures the amount of radiation energy (E) absorbed per unit mass (M) of the absorbing medium

• Medium must be specified 

Absorbed Dose (D)

[...]: reduction of energy as energy passes through matter 

Attenuation

[...]

• Typically low energy interactions in which radiation undergoes a change in direction but no changes in wavelength (aka energy) 

Coherent Scattering

Low energy photons are simply absorbed & causes a vibration of the electron cloud before it goes back to the same energy

Coherent Scattering

• Typically low energy interactions in which radiation undergoes [...] 

• a change in direction but no changes in wavelength (aka energy) 

Low energy photons are simply absorbed & causes a vibration of the electron cloud before it goes back to the same energy 

[...]

• Description
  

  • Photon interacts with outer orbital electron, imparting some energy to the outer orbital electron and ejects it from the orbit

    • Ejected electron is called the Compton electron, which has an energy equal to the excess imparted by the photon

  • Photon, as a result, is scattered with less energy due to the collision (less energy means larger wavelength in the end)

Compton Scatter

Compton Scatter

• Description
  

  • Photon interacts with outer orbital electron, imparting some energy to the outer orbital electron and ejects it from the orbit

    • Ejected electron is called the [...], which has an energy equal to the excess imparted by the photon

  • Photon, as a result, is scattered with less energy due to the collision (less energy means larger wavelength in the end)

Compton electron

Compton Scatter

• Description
  

  • Photon interacts with outer orbital electron, imparting some energy to the outer orbital electron and ejects it from the orbit

    • Ejected electron is called the Compton electron, which has an energy equal to the excess imparted by the photon

  • [what's the energy of the resultant photon?]

• Photon, as a result, is scattered with less energy due to the collision (less energy means larger wavelength in the end)

[...]

• Attempts to quantify biologic damage from deposition in tissues

Dose Equivalent (H)

[...]: source related term used to express intensity of an X-Ray

• Source is basically the anode

• Units
  

  • SI System --> Coulombs per kg (C/kg)

  • Non-SI System --> Roentgens (R) 

Exposure

Exposure: source related term used to express intensity of an X-Ray

• Source is basically the anode

• Units
  

  • SI System --> [...]

  • Non-SI System --> [...] 

• Coulombs per kg (C/kg)

• Roentgens (R) 

[...]: thickness of an aluminum absorber that is required to reduce beam intensity by 50%

Half-Value Layer

[...] = potential difference between cathode filament and anode target 

Kilovoltage (kVp)

[...] has the highest effective anatomic number, indicating it is best option for a shield 

Lead

[...]

• Energy absorbed by the medium per unit length of travel (keV per micrometer)

• Proportional to (particle charge) ²

Linear Energy Transfer (LET)

Linear Energy Transfer (LET)

• Energy absorbed by the medium per unit length of travel (keV per micrometer)

• Proportional to [...]

• (particle charge) ²

[...] and [...]

• Ultra high energy interactions with matter that blows the nucleus apart 

• They do NOT occur in the diagnostic x-ray energy ranges

• Might be helpful in radiation therapy 

Pair Production and Photodisintegration

Pair Production and Photodisintegration

• Ultra high energy interactions with matter that blows the nucleus apart 

• They do NOT occur in the diagnostic x-ray energy ranges

• Might be helpful in [...] 

radiation therapy

[...]

• Interaction with matter where x-ray is absorbed and not scattered 

Photoelectric Reaction

[...] 

• radiation that makes it through matter (could be the patient) to the other side 

Remnant Radiation