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Oral Radiology > Lecture 2 - Radiation > Flashcards

Lecture 2 - Radiation Flashcards

1
Q

Why is the tube head filled with oil?

A

Heat transfer from the photon

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2
Q

An incident electron directly striking a tungsten nucleus produces what?

A

Maximum energy Bremsstrahlung radiation

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3
Q

When the incident electron passes near the atom, but doesn’t hit it, what occurs?

A

Low energy Bremsstrahlung radiation

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4
Q

When an electron passes close to the nucleus and bend around it, when is produced?

A

Moderate energy Bremsstrahlung radiation (x-ray photon)

*The electron decelerates and bends, when this occurs, energy is given off

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5
Q

What element is the target for electrons?

A

Tungsten

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6
Q

Bremsstrahlung Radiation:

High energy

Moderate energy

Low energy

A

High - Some electrons directly collide with the tungsten nucleus - produces a high energy photon equal in energy to the incident electron

Moderate - Electrons pass close to nucleus - Decelerates and bends electron - Moderate energy photon given off

Low - Electrons pass at a distance from nucleus - deflected and slowed - Low energy photon given off

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7
Q

A 70 kVp tube head will produce x-rays with a max energy of how much?

A

70 keV of energy

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8
Q

What is characteristic radiation?

A

Incident electron hits another electron, and kicks it out of its orbital. This creates a void in the orbital, and a lot of energy is released in the form of photons

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9
Q

T/F - Characteristic radiation accounts for only a small fraction of x-ray photons generated.

A

TRUE

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10
Q

The tungsten characteristic X-ray is found at what photon energy?

A

59 keV

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11
Q

The cathode is __________

The anode is ___________

A

Negative

Positive

*This is opposite of common sense

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12
Q

What is the cathode made of?

How does it work?

A

Tungsten filament and molybdenum focusing cup.

Low voltage heats the filament, and this produces a cloud of electrons. The molybdenum cup focuses the electrons into a narrow beam

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13
Q

What is the anode made of?

How does it work?

A

Tungsten target and copper stem

Electron stream turned into x-rays and heat

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14
Q

Why is the X-ray tube in a vacuum?

A

It helps prevent burnout of the filament, also no oxidation

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15
Q

What is the element used as the typical target on the anode?

A

Tungsten

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16
Q

What is the focal spot?

A

The point on the target where the stream of X-ray photons originate.

17
Q

What does the low voltage tube current do?

A

Heats the tube filament - this generates a stream of electrons b/t the cathode and anode

18
Q

What does the high tube voltage current do?

A

It accelerates the electron stream from the cathode to the anode to a level that X-rays can be produced (80,000 volts)

19
Q

What does the step-down filament transformer do?

A

Reduces incoming voltage (110-120V) to approximately 3-5 volts needed to heat the filament

20
Q

What does the step-up transformer do?

A

Provides large electrical force needed to propel electrons from cathode to anode (from 110-120 V to 60,000 to 100,000 V)

21
Q

What is the auto transformer and what does it do?

A

It is controlled by the kVP dial on control panel. It varies the voltage to the step-up transformer to achieve the desired kVp to the tube

22
Q

What is the most frequent source of malfunction in the X-ray tube?

A

Filament burnout

*Keep the machine on during the day. More strain occurs when it is repeatedly warmed and cooled by being turned on and off repeatedly

23
Q

How do you increase the energy of the emitted X-ray beam?

A

Increase power to the high voltage step up transformer. This increases the acceleration of the electrons from cathode to anode, resulting in an energy increase

24
Q

Doubling the exposure time _________ the exposure.

A

Doubles

25
Q

If tube current increases, what happens to the quantity of X-rays?

A

Higher quantity

26
Q

What does the body absorb better (what is more dangerous), high kV or low kV?

A

LOW kV.

*Counter-intuitive, but the higher the kV, the more the rays pass thru the tissue instead of being absorbed

27
Q

What is kVp?

A

Tube voltage

28
Q

If the potential b/t the anode and cathode increases, then what happens to the energy of each electron when it strikes the target?

A

Increases

*THIS INCREASES EFFICIENCY OF THE CONVERSION OF ELECTRON ENERGY INTO X-RAY PHOTONS

**INCREASE IN kVp INCREASES X-RAY PENETRATION OF MATTER

29
Q

What is filtration and what is used?

A

It absorbs low energy photons that would not reach the image receptor

Aluminum filters absorb these low energy photons

30
Q

What is a collimator?

A

Metal barrier used to reduce the size of X-ray beam

*Lined with lead to absorb stray photons

**Reduces scatter radiation and the patient surface exposed

31
Q

The intensity of the X-ray beam is __________ proportional to the square of the distance b/t the source and the target.

A

Inversely

*If I’m 1 foot away, my exposure is 1. If I’m 2 feet away, my exposure is 1/4. If I’m 3 feet away, my exposure is 1/9.

32
Q

A radiograph come out underexposed. How do you try to correct the exposure on a retake? (2 ways)

A

Increase kVp on control panel

Increase exposure time

33
Q

What is photoelectric absorption?

A

Incident photons are absorbed by an atom by interacting with inner shell electrons.

This produces the lighter areas on the film, making radio graphic imaging possible

Black on a radiograph means space because all the rays go direct to the film

34
Q

Photoelectric absorption depends on the _______ and _______ thickness of the object, which creates the contrast b/t different tissues.

A

Density

Thickness

35
Q

What is coherent scattering?

A

Low energy photons are deflected by OUTER ring electrons

*Only about 7% of interaction for dental X-rays, and contributes very little to film fog

36
Q

What is Compton scattering?

A

Photon interacts with OUTER orbital electron

*Accounts for about half of interactions in dental X-rays

**These darken and degrade the image while carrying no useful information

37
Q

What is beam attenuation?

A

Lower energy photons are more readily absorbed, while an increase in energy results in an increase of transmission of the beam thru the absorbing tissue

Oral Radiology (7 decks)

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