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Physics > Basics > Flashcards

Basics Flashcards

1
Q

What is the wavelength of Xrays?

A

0.01 to 10 nm

Hard X rays 0.1-0.2 nm–> Higher Energy and used in medical imaging

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2
Q

What eV does a photon need to be ionizing?

A

15 eV

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3
Q

Where do Gamma Rays originate?

A

Nuclei of an Atom

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4
Q

What does the binding force inversely proprotional to?

A

Square of the distance between the nucleus and the electron shell

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5
Q

What is the K Shell Binding Energy of Tungstun?

A

-69.5 kEV

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6
Q

Why do you add rhenium to the Tunsten filament?

A

To prevent cracking from multiple cycles of healing and cooling

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7
Q

What is Thermionic emission?

A

Heat the filament–> Kinetic energy–> Electrons “boil off”

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8
Q

Why is there a glass tube around the anode and cathode?

A

To create a vacuum which allows you to control the speed and amount of electrons

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9
Q

What is the space charge effect?

A

At the filament (Cathode, neg charge), which the elctrons boil off, a space cloud forms around the filament (neg), but as they boil off the cathode starts to have a slightly positive charge that pulls in the cloud. Once equilibrium is reached, additional boiled electrons will result in another electron leaving the cloud.

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10
Q

What is a focusing cup?

A

Metallic cup places around filament to help the electrons hit the anode at an acceptable size.

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11
Q

Actual focal spot versus effective focal spot

A

Actual is where the electrons hit the anodes. Effective is where it hits the patient

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12
Q

How do you dissapate heat at the anode?

A
  1. Rotating Anode

2. Angle the Anode

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13
Q

How does the Anode angle affect focal spot?

A

Smaller (steeper) angle= Smaller focal spot but more heel effect

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14
Q

What makes the heel effect worse?

A
  1. Smaller Anode Angle
  2. Small focus to film distance
  3. Large Field of View
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15
Q

How can you make the heel effect better?

A
  1. Larger Anode Angle
  2. Larger Focus to film distance
  3. Small Field of view
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16
Q

What is the difference between keV and kVp

A 
kVp= the PEAK kilovoltage
keV= The kilovoltage of one electron
17
Q

What is Brehmstalung?

A

Braking Radiation that creates a continunum of x ray energies based on how close to the nucleus it deviates.

18
Q

What determines the highest and lowest energy and the bremstrahlung curve?

A 
Higher= Max kVP
Lowest= Depends on the Filter used
19
Q

What is the amount Brehmstrahlung interactions proportional to?

A
  1. Incoming energy of the charged particle

2. Atomic Number (higher= better)

20
Q

What is beam intensity?

A

Number of X rays multipled by energy (R/min)

Intensity is proportional to kVp squared

21
Q

How does changing Target Material effect Brehmstrahlung and Characteristic Radiation?

A
  1. Higher Z= more Brehmstrahlung= more quantity

2. Higher Z= Different atomic number= Change in Quality

22
Q

How does increasing kVP affect quality and quantity?

A
  1. Increased max energy
  2. Increased average X ray energy (quality)
  3. Increased total x rays produced (quantitity)
23
Q

What is the 15% rule?

A

Increased kVP by 15%, decreased mA by half to maintain same X ray density

24
Q

How does a single phase generator compare to the triple phase generator?

A

Truple phase has more quality and quantity

25
Q

What is HVL?

A

Amount of material needed to attenuate half the x ray

26
Q

What does HVL depend on?

A
  1. Target Material
  2. Beam Filtration (more filtered= higher average energy= higher HVL)
  3. kVp

Does NOT depend on mA

27
Q

what is the 10th HVL?

A

Thickness to attenuate X ray 90% (used for shielding)

28
Q

How does a filter affect the beam energy?

A 
Decreases quantity (less under the curve)
Changes quality by increased the average energy
29
Q

What is the average Bremstrahlung energy?

A

1/3 to 1/2 the kVP

30
Q

What is an Auger Electron?

A

Characteristic X ray hits an outer shell electron and ejects that electron instead (most common in lighter element, soft tissues)

31
Q

How do mA and kVp affect focal spot?

A
  1. Increased mA and low kVP increases focal spot

2. High kVP decreases the focal spot

32
Q

What is stray radiation?

A

The sum of leakage and scatter.
Leakage: X rays that transmit through housing
Scatter: Deflected X rays

33
Q

What is the dose for DEXA

A

0.001 mSV

Physics (10 decks)

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