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Radiology Principles Class > Unit 2 X-Ray Interaction With Matter > Flashcards

Unit 2 X-Ray Interaction With Matter Flashcards

1
Q

Define Attenuation

A

The reduction in the number of photons as it passes through matter

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2
Q

What are the 3 possible scenarios that can occur when x-rays strike matter?

A

Absorption: photon is absorbed by the tissue(dose)
Transmission: photon passes through without interaction and hits the IR
Scatter: photon interacts with the body, is deflected, and continues in a new direction

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3
Q

Coherent Scatter Types

A

-Thomson: one electron excited
-Raleigh’s: all electrons excited

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4
Q

Characteristics of Coherent Scatter interaction

A

-Low energy primary photon interacts with all of the electrons in the atom(< 10keV)
-Atom becomes excited
-Atom releases a SCATTERED PHOTON with the same energy as the INITIAL PHOTON

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5
Q

Coherent Scatter impact on the body

A

-Unmodifying: no ionization
-No dose to the patient

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6
Q

Coherent Scatter conditions

A

-LOW energy x-ray photon
-All tissue types and densities

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7
Q

Coherent Scatter impact on Image

A

Minimal degradation of image (if any)

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8
Q

X-rays produced in the body are __________ x-rays

A

Secondary

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9
Q

Photoelectric Absorption characteristics

A

-Diagnostic energy (25-140 keV)
-Inner shell electron is EJECTED
-Photon is absorbed
-Characteristic cascade occurs
-Weak secondary x-rays

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10
Q

Photoelectric Absorption: Auger Effect

A

Ejected electron bombards into another electron and ejects it

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11
Q

Photoelectric Effect Impact on the body

A

-Diagnostic range x-rays are absorbed by tissue
-Photoelectric(PE) = x-ray absorption and ionization = radiation patient dose
-Absorption= structures are visible on an x-ray image

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12
Q

Absorption on image shows up ________, Transmission shows up _________

A

White; Black

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13
Q

Photoelectric Absorption conditions

A

-Photon energy must be slightly higher than the binding energy(BE) of the electron
-PE increases with increased atomic #
*Bone: high atomic number (13) = absorbs more x-rays
*Air and Soft tissue: low atomic number (7) = absorbs less x-rays
-Higher atomic density of tissue= increased chance of Photo Electric effect

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14
Q

Photoelectric Effect impact on image

A

Image formation

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15
Q

Compton Scatter characteristics

A

-The energy of the incident photon is in the diagnostic range (Diagnostic energy (25-140 keV))
-Photon bombards into OUTER shell electron and ejects it
-Photon continues on in a new direction
-Photon may undergo additional Compton interactions until it is absorbed Photoelectrically
-The higher the angle of deflection, the weaker the photon becomes
-Forward scatter is still highly penetrating

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16
Q

T or F: Photoelectrically is the only way a photon is absorbed

A

True

17
Q

Compton scatter: Define Backscatter

A

Photon directed back towards the tube

18
Q

Compton scatter impact on the body

A

-Ionization of atoms: biologic damage
-Increase of patient dose
-Source of occupational exposure(patient is source of exposure, scattered photon from patient can hit radiographer)
-Compton scattered photon will be absorbed photoelectrically

19
Q

Lead symbol and atomic #? What does it do?

A

-Pb; 82
-Absorbs Compton scatter Photoelectrically and reduces occupational exposure

20
Q

High atomic # = high rate of ______

A

PE(Photoelectric)

21
Q

Compton Scatter conditions

A

-Occurs at all photon energy levels
-Occurs at any atomic number
-Increases with increased tissue density and increased tissue volume

22
Q

More matter means…

A

More scatter

23
Q

Compton Scatter impact on Image

A

Degradation of the image

24
Q

Describe how kVp impacts the amount of PE vs Compton in a given x-ray exposure

A

PHOTOELECTRIC:
-Low kVp INCREASES the chance of photoelectric
* LOW energy photon will be ABSORBED in the body
-High kVp DECREASES the chance of photoelectric
*HIGH energy photon will PENETRATE through the body

COMPTON:
-High kVp INCREASES the percentage of photons that undergo Compton
-High energy beams produce high energy scatter photons

25
Q

Optimum kVp is used to…

A

Allow maximum penetration while keeping scatter to a minimum

26
Q

_____ depends on what you’re x-raying, _____ depends on how much you’re x-raying

A

kVp; mAs

27
Q

Low kVp

A

-More absorption
-Less transmission
-Less scatter

(more PE, less Compton + Transmission)

28
Q

High kVp

A

-Less absorption
-More transmission
-More scatter

(less PE, more Compton and Transmission)

29
Q

How does obesity affect the amount of Compton in an exposure?

A

-Less tissue = less scatter
-More tissue = more scatter, increase mAs

30
Q

Additive vs Destructive Pathology

A

-Additive: If a disease causes the affected body tissue to increase in thickness, effective atomic number, and/ or tissue density, there will be a greater attenuation of the x-ray beam. Often requires an increase in technical factors like kVp and mAs

-Destructive: If a disease causes the affected body tissue to decrease in thickness, effective atomic number, and/or tissue density, there will be less attenuation of the x-ray beam. Often requires a decrease in technical factors like mAs and kVp

31
Q

Define Recoil electron

A

An outer shell electron that is ejected from its orbit during Compton scatter

32
Q

Define Angle of deflection? What interaction has this?

A

-The angle formed by the incident photon trajectory after collision with an outer shell electron
-Compton scatter

33
Q

Secondary radiation happens in which interaction?

A

Photoelectric

34
Q

The higher the deflection Angle, the ___________ the photon becomes.
The smaller the deflection Angle, the ___________ the photon becomes.

A

Weaker; Stronger(more energy)

35
Q

The chance of a Compton event occuring ______________ as tissue density increases

A

Increases

36
Q

The chances of a Compton event occuring __________________ as tissue thickness increases

A

Increases

37
Q

Photoelectric effect, Coherent scatter, Compton scatter photons and electrons

A

Photoelectric: 1 photon in, 1 electron out
Coherent: 1 photon in, 1 Scattered photon out
Compton: 1 photon in, 1 electron and 1 scattered photon out

Radiology Principles Class (10 decks)

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