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physics - common equipment > Chapter 8 > Flashcards

Chapter 8 Flashcards

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1
Q

What factors affect beam attenuation?

A

Part thickness, atomic composition, and tissue density, and energy level of the beam

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2
Q

What type of radiation forms the latent image?

A

Exit radiation

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3
Q

What are the interactions that occur when the primary beam passes through the body?

A

Absorption
Scatter
Transmission

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4
Q

When does complete x-ray absorption occur?

A

When the xray photon has enough energy to eject an inner-shell electron from an atom

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5
Q

When does ionization occur?

A

When an electron is ejected

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6
Q

In the diagnostic energy range, absorption is known as:

A

Photoelectric effect

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7
Q

What happens during a photoelectric event?

A

An atom is ionized, creating a vacancy in the inner shell

Electrons drop down from the outer valence to fill the created vacancy creating secondary photons

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8
Q

What determines the probability of absorption?

A

Initial energy of the incoming x-ray photon

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9
Q

What must the photon energy be to cause ionization?

A

Equal to or greater than the inner shell binding energy

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10
Q

When does Coherent scatter occur?

A

When an incoming photon is not absorbed, but instead loses energy while interacting with an atom

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11
Q

What are the two forms of scatter?

A

Compton and Coherent

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12
Q

When does Compton scattering occur?

A

Incoming photon transfers some of it’s energy to an atom, causing ionization

Incoming photon moves past the atom, and continues on a path through the body with less energy

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13
Q

What is the ejected electron called during ionization?

A

Compton electron or secondary electron

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14
Q

What affects the probability of compton scattering?

A

Probability increases as energy increases

Probability is not dependent on tissue density or atomic structure

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15
Q

When does Coherent scattering occur?

A

With low-energy x-rays

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16
Q

What happens to the photon during Coherent scattering?

A

The photon interacts with the atom, exciting it

The photon does not lose energy, but it does change direction

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17
Q

How much does attenuation increase due to tissue thickness?

A

Attenuation increases 50% for each 4-5 cm of increases tissue thickness

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18
Q

How does tissue type affect attenuation?

A

Higher atomic number, such as bone, attenuate more radiation

Lower atomic number, such as fat, attenuate less radiation

19
Q

How does atomic composition affect absorption and scatter?

A

The higher the atomic number, the more opportunities for scatter or absorption

20
Q

How does tissue density affect attenuation?

A

The more dense the tissue, the greater chance of attenuation

21
Q

How does tissue density affect absorption or scatter?

A

The more dense the tissue, the greater chance for absorption or scatter

22
Q

What are the 4 types of tissue from least dense to most dense?

A

Air
Fat
Muscle
Bone

23
Q

What is scattered radiation that contributes to an unwanted receptor exposure?

A

Fog

24
Q

What creates the white of an image?

A

Absorbed radiation

25
Q

What creates the black of an image?

A

Trasmitted radiation

26
Q

What creates the gray of an image?

A

Scatter radiation

27
Q

What percent of the primary beam reaches the IR?

A

Less than 5%

28
Q

The latent image is processed into the:

A

Manifest image

29
Q

Describe the cassette used in film-screen

A

Light-tight container that holds radiographic film

The film is sandwiched between two intensifying screens and the cassette

30
Q

How is an image created with film-screen IRs?

A

Exit radiation interacts with the screen and is converted into visible light

Visible light interacts with the radiographic film, imprinting the latent image

The latent image is processed chemically to create the manifest image

31
Q

What are the two types of digitial image receptors?

A

CR - computed radiography

DR - digital radiography

32
Q

How is an image created using CR?

A

Cassette based system - radiographic film is replaced with an imaging plate that is removed the from cassette and scanned by a CR scanner

The CR scanner coverts the latent image contained in the IP into data that is turned into the manifest image seen on the computer

33
Q

What is used in CR and DR to create the manifest images?

A

Algorithms

34
Q

Digital image receptors are able to respond to a wide range of x-ray exposures - this is called:

A

Dynamic range

35
Q

What is the benefit of a wide dynamic range?

A

Less radiation is needed to produce a diagnostic image

36
Q

What is the disadvantage of dynamic range?

A

Dose creep - digital algorithms are able to correct overexposure, allowing techs to fall into a bad habit of using more radiation than needed

37
Q

How are digital images displayed?

A

As a matrix

38
Q

What is a matrix?

A

A combination of rows and columns made up of pixels

39
Q

What is a pixel?

A

A small square representing a single numerical value, which translates to a single brightness for that one pixel in the image

40
Q

Are digital images impoved with smaller or larger matrix sizes? Smaller or larger pixels?

A

Larger matrix, smaller pixels

Larger matrix sizes = more pixels

41
Q

How is the numerical value determined for each pixel?

A

Attenuation of x-rays

Pixels that receive greater amounts of radiation correlate to darker areas

Pixels that receive less amounts of radiation correlate to lighter areas

42
Q

What does bit depth determine in an image?

A

Amount of different shades of gray that can be displayed

43
Q

Difference between static and dynamic?

A

Static - motionless
Dynamic - moving

44
Q

How is fluoro different from general diagnostic radiography?

A

Fluoro uses dynamic imaging, and the x-ray tube is under the table with an image intensifier above the patient

physics - common equipment (7 decks)

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