X-ray interaction w/ matter

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15 Terms

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Factors Affect Scatter

Patient thickness

Tissue density

kV Energy

Field Size

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5 Types of Scatter Radiation

Classical
Compton
Photoelectric
Pair Production
Photodisentigration

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Scatter Radiation - Classical

Interaction between low energy x-rays and entire atom

Below 10 kV

No ionization in this interaction

X-ray photon loses no energy

Wavelength of incident x-ray = wavelength of scattered x-ray (photon)

<p><span style="color: rgb(255, 255, 255);"><span>Interaction between low energy x-rays and entire atom</span></span></p><p><span style="color: rgb(255, 255, 255);"><span>Below 10 kV</span></span></p><p><span style="color: rgb(255, 255, 255);"><span>No ionization in this interaction</span></span></p><p><span style="color: rgb(255, 255, 255);"><span>X-ray photon loses no energy</span></span></p><p><span style="color: rgb(255, 255, 255);"><span>Wavelength of incident x-ray = wavelength of scattered x-ray (photon)</span></span></p>
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Scatter Radiation - Classical Also called 4 names:

– Coherent
– Rayleigh
– Unmodified
– Thompson

<p><span style="color: rgb(255, 255, 255);"><span>– Coherent</span></span><span style="color: rgb(255, 255, 255);"><br></span><span style="color: rgb(255, 255, 255);"><span>– Rayleigh</span></span><span style="color: rgb(255, 255, 255);"><br></span><span style="color: rgb(255, 255, 255);"><span>– Unmodified</span></span><span style="color: rgb(255, 255, 255);"><br></span><span style="color: rgb(255, 255, 255);"><span>– Thompson</span></span></p>
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Scatter Radiation - Compton/Modified

Interaction between moderate energy x-rays and atom

Interacts with outer shell electrons

Ionization occur

Photon changes direction
– photon can be redirected back towards source
(backscatter)

<p><span style="color: rgb(255, 255, 255);"><span>Interaction between moderate energy x-rays and atom</span></span></p><p><span style="color: rgb(255, 255, 255);"><span>Interacts with outer shell electrons</span></span></p><p><span style="color: rgb(255, 255, 255);"><span>Ionization occur</span></span></p><p><span style="color: rgb(255, 255, 255);"><span>Photon changes direction</span></span><span style="color: rgb(255, 255, 255);"><br></span><span style="color: rgb(255, 255, 255);"><span>– photon can be redirected back towards source</span></span><span style="color: rgb(255, 255, 255);"><br></span><span style="color: rgb(255, 255, 255);"><span>(backscatter)</span></span></p>
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<p><span>Scatter Radiation - Compton/Modified is responsible for…</span></p>

Scatter Radiation - Compton/Modified is responsible for…

majority of scatter radiation reaching image receptor (IR), contributes most to occupational exposure 

<p><span style="color: rgb(255, 255, 255);"><span>majority of scatter radiation reaching image receptor (IR),&nbsp;contributes most to occupational exposure&nbsp;</span></span></p>
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During Fluoro – the patient is the…

largest scattering object

<p><span style="color: rgb(255, 255, 255);"><span>largest scattering object</span></span></p>
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Compton scatter contribute to increases in…

fog which decreases the contrast in the radiograph

<p><span style="color: rgb(255, 255, 255);"><span>fog which decreases the contrast in the radiograph</span></span></p>
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Scatter Radiation - Photoelectric

Ionization occurs when inner shell electron is ejected

Incident photon disappears, photoelectron is ejected

Incident photon has to be greater than K shell electron energy

Inner shell electron is ejected, outer electron fills the orbit-producing characteristic radiation

Contributes significantly to patient dose

<p>Ionization occurs when inner shell electron is ejected</p><p>Incident photon disappears, photoelectron is ejected</p><p>Incident photon has to be greater than K shell electron energy</p><p>Inner shell electron is ejected, outer electron fills the orbit-producing characteristic radiation</p><p>Contributes significantly to patient dose</p>
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Metal or high atomic number elements will have…

more photoelectric absorption

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Pair Production

Occurs at 1.02 MeV or higher
• High energy photon comes close to nucleus
and loses it’s energy
• 2 particles are emitted with opposing
electrostatic charges- negatron & positron

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Pair Production 2

Negatron is quickly absorbed
• Positron combines with a free electron
• When positron & electron combine- they
annihilate each other
• This gives rise to 2 photons of 0.51 MeV each

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Photodisintegration

Occurs with photon energies of 10 M eV or higher
• High energy photons strikes nucleus
• Nucleus becomes excited

Ejects a nuclear fragment

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Importance of Interactions of X-rays w/ Matter

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kVp determines type of interaction in the body

High kV decrease in photoelectric absorption and increases Compton interaction (more penetration and less body
interaction)

Low kV increase in photoelectric absorption, Increase in patient dose