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IMAG 311- Med Img Fundmts & Physics > Interactions > Flashcards

Interactions Flashcards

1
Q

Photoelectric (PE) Absorption

A

Incident photon energy is completely absorbed by an inner shell electron
-occurs when x-ray photon has just slightly more energy than the Eb (binding energy of the electron) of a k or l-shell electron

  • x-ray photon knocks the inner shell electron of an atom out of orbit causing the atom to ionize
  • *Patient tissues DO absorb radiation during this interaction**
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2
Q

What type of electron goes along with PE absorption?

A

Photo electron

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3
Q

How can the photoelectron energy be determined?

A

Ei = Eb + Eke

  • Ei: energy of incident photon
  • Eb: binding energy of the electron
  • Eke: Kinetic energy of the photoelectron
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4
Q

Characteristics of Photoelectron

A
  • Kinetic Energy
  • Mass
  • Reabsorbs quickly
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5
Q

Characteristic Cascade

A
  • Vacancy filled by an outer shell electron
  • electron undergoes change in energy level
  • emits characteristic photon
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6
Q

Secondary Radiation

A

-when a characteristic photon are emitted from atoms of the patient after PE absorption interaction has occurred
radiation that originates from irradiated material outside of xray tube

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7
Q 
PE Absorption is most influenced by what?
A. Subject volume
B. Subject thickness
C. Subject mass density
D. Subject atomic #
A

D. Subject atomic #

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8
Q

As you increase kVp (increasing photon energy), what happens to the probability of absorption?

A

Decreases by 1/8 (inverse cubed relationship)

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9
Q

Low atomic number materials and soft tissue result in what?

A

-photoelectrons maintaining the majority of the incident photon’s energy.

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10
Q

What interactions are both energy and atomic number dependent?

A

Photoelectric Interactons

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11
Q

When kVp decreases the, what happens to the probability of interactions (PE and Compton)?

A

The probability of Interactions of PE or Compton decrease

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12
Q

Attenuation

A

The absorption or scatter of a beam as it travels through a target material

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13
Q

Coherent Scatter

A

Involves low energy photons (below 10 keV)
-Can also be called unodified scatter, classical scatter, thompson (single outer-shell e), or rayleigh (all electrons of the atom)

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14
Q

Transmission of an x-ray

A

When x-rays pass through a patient instead of being absorbed

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15
Q

Compton Scatter

A 
Incident photon (Ei) interacts w. outer shell electron and knocks it out of orbit
-incoming xray does not lose all of its energy; it becomes a scattered xray photon and continues in a different direction with a lower amount of energy
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16
Q

In what interaction is the energy of the incident photon shared between the scattered photon and the KE of the orbiting electron that was knocked out of its orbit?

A

Compton Scatter

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17
Q

interactions that happen at low xray energies such as in mammography are called what?

A

Unmodified (coherent) scattering

-Instead of the atom losing an electron, the electron or atom vibrates and redirects incident photons

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18
Q

Which Interaction creates the vast majority of scatter in the range of xray energies used in diagnostic imaging?

A

Compton Scatter

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19
Q

What 3 variables affect the quality of an xray beam?

A

Part thickness, atomic number, and tissue density

20
Q

if a tissue made out of a substance with a very low atomic number and fewer inner shell electrons make up the tissue, then the chance of photoelectric absorption interactions increases or decreases?

A

Decreases

21
Q

Which atom would have an increased chance of photoelectric absorption occuring, calcium or oxygen and why?

A

Calcium, because it has a bigger atomic number, and there are more electrons orbiting around the nucleus for an incident photon to interact with than in an oxygen atom

22
Q

Tissue density affects how tightly bound atoms are in any given tissue.
True or False?

A

True

23
Q 
Which of the 4 major body tissues has the greatest effective atomic number
A. Bone
B. Muscle
C .Fat
D. Air
A

A. Bone

24
Q

What is the effective atomic number for Bone

A

14 (calcium)

25
Q

What is the predominant interaction taking place between bone and the x-ray beam?

A

Photoelectric Absorption

26
Q

Muscle is not the most difficult tissue for an x-ray beam to penetrate
True or False?

A

False…Muscle is the most difficult tissue for an x-ray beam to penetrate

27
Q

Less photoelectric absorption and more Compton scatter happens in what body tissue?

A

Muscle

28
Q

What two factors make fat easier for the x-ray beam to penetrate?

A

Both its atomic number and density being less than the other body tissues

29
Q

Why doesn’’t air attenuate more of the primary beam than muscle or fat?

A

Because air’s tissue density is much, much lower than muscle or fat.
-Therefore, air doesn’t absorb any of the x-ray beam at all.

30
Q

Thicker parts cause more beam scatter and greater secondary radiation.

True or False?

A

True

31
Q

increased kVp exposure produces more scatter and secondary photons in the patient that tend to travel in What direction?

A

a forward direction, toward the image receptor.

32
Q

The Compton interaction, which occurs between what three things?

A

The signal, x-ray beam, and the patients tissue

33
Q

Noise

A

The source of noise is anything that prevents information from reaching an image receptor.

34
Q

Sources of Noise?

A
  • Reduced signal strength from thicker parts
  • incorrect use of an anti-scatter grid and too few x-ray photons making it through the patient, table or grid
  • Scatter is also an example of noise
35
Q

Pair Production

A
  • When a super energetic photon enters an atom and interacts with the nucleus–nucleus can’t hold all of the energy, so it is given off as a negatron and positron
  • Nucleus becomes unstable - — Happens in therapy and PET scans
36
Q

Increasing kVp does what to the total attenuation?

A

Decreases total attenuation

37
Q

When kVp is increased extremely, what happens regarding PE Absorption and Compton Scatter?

A

PE Absorption decreases

Compton Scatter increases

38
Q

Photodisintegration

A

Happens with extremely high energy photon

  • Absorption of photon by nucleus
  • excited nucleus releases alpha particle
  • *Not significant in imaging
39
Q

As kVp increases,the # of photons transmitted without interactions increases or decreases?

A

Increases

40
Q

As kVp increases and the # of photons increases, what does this do to the PE and Compton interactions?

A

Decreases the probability of PE absorption and Compton interactions

41
Q

Within the attenuated beam… As kVp increases

A

PE absorption decreases
Compton increases

  • Increases percentage of scatter
  • Decreases percentage of absorption
42
Q

Differential Absorption

A

The difference in what is transmitted through different body parts
-result in image contrast

43
Q

Mass Density

A

Relates to how closely atoms are located within a material

44
Q

As Mass density increases, the space between atoms ___?

A

decreases

45
Q

X-ray transmission is reduced as what increases?

A

Mass Density

46
Q

Mass Density and X-ray attenuation coefficients are inversely proportional
True or False?

A

False, they are directly proportional–if you double the mass density, the the x-ray attenuation coefficients doubles

IMAG 311- Med Img Fundmts & Physics (6 decks)

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