X-ray Interactions with Matter

Attenuation

The reduction in the number of x-ray photons (intensity) of the primary beam and the resulting loss of energy, as the beam passes through matter

Attenuation includes both ______ and scattering

Absorption

Attenuation is influenced by:

1. Tissue type (atomic #)

2. Subject thickness/volume of tissue-subject density

3. Photon quality-energy/quality (kV)

mA does not affect the probability of attenuation; however, it can impact the amount or number of photons attenuated

False

When x-ray photons interact with human tissue atoms, the initial x-ray photon may:

1. Scatter or change direction (deflected)

2. Be completely absorbed

3. May pass through matter and not interact

These are x-rays that pass through the patient and interact with the image receptor

Transmitted or remnant beam

As kVp increases, the total number of photons which are transmitted without interaction ______

Increases

With an increase in kVp, the percentage of _______ interactions decreases while the percentage of Compton interactions ________

Photoelectric, increases

At low energies, most x-ray interactions with tissue are?

Photoelectric

As photons energy increases, the chance of photoelectric interactions ______ drastically

Decreases

At approximately 50 kVp, the number of Compton verses Photoelectric interactions are?

Equal

As the atomic number of an atom increases, the probability of a Compton interaction increases

False

Binding Energy

The energy required to remove orbital electron from its shell

For any given atom, the ____ shell electrons possess the highest binding energy

K

Elements with a higher atomic number will have a _____ k-shell binding energy

Higher

Electrons further from the nucleus require less energy to remove them from their orbits and therefore possess a ______ total “net” energy

Greater

Regarding the Compton Effect: a relatively high-energy x-ray photon ejects or removes a loosely bound, outer-shell electron

True

Regarding the Compton Effect: The ejected electron is referred to as a Compton or “recoil” electron

True

Regarding the Compton Effect: The incident (original) photon is completely absorbed in the process

False

Regarding the Compton Effect: Can be mathematically expressed as Ei= Es + Eb + Eke

True

Regarding the Compton Effect: is the least common interaction in the human body

False

The ______ is the single most important scattering object in both radiography and fluoroscopy

Patient

Scatter radiation emitted from the patient is the primary source of ________ exposure

Occupational

Relatively low-energy x-ray photon interacts with and ejects an inner-shell electron

Photoelectric

Incident x-ray photon interacts with loosely bound, outer-shell electron

Compton

Ejected electron is known as a Compton or “recoil” electron

Compton

These interactions are more likely to occur in bone than in soft tissue

Photoelectric

Responsible for the majority of scatter reaching the IR

Compton

Contributes mostly to patient dose

Photoelectric

Is a partial energy transfer

Compton

An electron vacancy or hole causes a characteristic cascade

Photoelectric

This interaction between x-ray photons and tissue is responsible for subject contrast and also contributes significantly to patient dose

Photoelectric

This interaction is more likely to occur with absorbers having a high atomic number, such as positive contrast media

Photoelectric

What happens to the incident x-ray photon during the Photoelectric Effect?

X-ray photon is absorbed and no longer exists

How is the Photoelectric Effect mathematically expressed?

Ei = Eb + Eke

A photoelectric interaction is more likely to occur when the x-ray photon energy and the electron binding energy are nearer to one another

True

What is true about this image?

• Is the total energy transfer from photon to electron

• Interaction is more likely to occur in bone than in soft tissue

What is true about this image?

• Interaction of very low-energy x-ray photons (below 10keV)

• Is called coherent, classical, or unmodified scattering

• Has little effect on image quality; insignificant in diagnostic radiology

What is this image demonstrating?

Pair production

For pair production: Interaction between high-energy photons, at least _____ MeV, and matter

1.02

For pair production: A high-energy incident photon comes close to a strong _____ field and loses all of its ____ in the interaction

Nuclear, energy

For pair production: Energy is used to create ____ of electrons, a negation and a positron

Pair

For pair production: After the annihilation reaction, each photon possesses ____ MeV

0.51

Pair production _____ occur in diagnostic x-ray

Does not

Subject Density

How tightly packed at atomic level, not the thickness of the part

The probability of Compton scattering does not depend on the atomic number of an atom

True

How many more times is it likely that an x-ray photon will undergo a photoelectric interaction in bone verses soft tissue?

7 times greater

3 things that influence x-ray photon beam attenuation:

• Tissue type

• Subject thickness

• Photon quality

Rank (water, bone, air, fat, muscle) from greatest amount of attenuation to least amount of attenuation

Bone, muscle, water, fat, air

At 50 kVp, what percentage of photons are attenuated in 10 cm of tissue?

>99%

At 130 kVp, what percentage of photons are transmitted in 10 cm of tissue?

6%