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Physics > Radiology > Flashcards

Radiology Flashcards

1
Q

What is the atomic number?

Mass number A?

A
  1. Protons
  2. Neutrons and protons
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2
Q

What is the binding force of the k - electron of tungsten?

A
  • 69.5 keV

Remeber it is negative

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3
Q

How many electrons does the k-shell hold? L shell?

A

2 in K

8 in L

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4
Q

What charge is the cathode?

A

negative and is the filament

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5
Q

Which has more amps and which has more voltage- the filament or the tube?

A

Filament has more Amps

Anode or tube has more volts.

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6
Q

What is the purpose of the glass tube?

A

Maintain a vaccum… reduce scatter and allow control of the speed and the amount of x-rays

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7
Q

What is thermionic emission?

A

Boiling off electrons

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8
Q

What is the filament made out of?

A

Tungsten and rhenium

Tungsten has a lot of electrons and a high boiling point

Rhenium reduces cracking

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9
Q

What percentage of energy are transimitted to x-rays?

A

1%

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10
Q

What is the space charge effect?

A

The boiled electrons hold close to the filament and over time create a charge that limits the boiling off of more electrons.

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11
Q

What is the relationship between mA and electrons?

A

Higher mA = more electrons (Quantity)

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12
Q

What effect does a steeper/smaller angle have on the effective focal spot and the heel effect?

A

Smaller effective focal spot

Larger heel effect

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13
Q

What side of the x-ray tube is the heel effect the worst?

A

Anode side… more target the x-rays have to penetrate to leave the tube.

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14
Q

What improves the heel effect?

A

Large anode angle or shallow

Larger focus to film distance (works like an air gap where you miss the heel effect)

Smaller FOV (again, miss the detector)

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15
Q

What are the three interactions between the target and electrons?

A

Excitation = heat = most interaction

Brems - braking (polychromatic)

Characteristic

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16
Q

What causes more brems?

A

Higher z —- this makes the k-electrons harder to knock off

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17
Q

What factors influence Beam intensity (the shape of the brem curve)?

A

kVp

mA

Target material (brems vs characteristic)

Filtering

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18
Q

What is the Z of tungsten? Molybdenum?

A

74 tungsten

42 Moly

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19
Q

Beam intensity is proportional to kVp how?

A

BI = (kVp)2

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20
Q

WHat is the 15% rule?

A

Increase kVp by 15% you have to decrease mA by 50% to maintin the same density.

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21
Q

Does voltage ripple affect Quality or Quantity?

A

Both

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22
Q

A lot of filtration needed to attentuate an x-ray beam that means what when discussing the beam’s half life value?

A

Higher HLV

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23
Q

What is the half-life value?

A

The amount of material needed to attenuate an x-ray beam by 1/2

Determinded by kVp and Z (basically what makes the energy level higher)

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24
Q

How many HVL are needed to attenuate the x-ray by 90% (TVL)?

A

10

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25
Q

How is an auger electron created and what else is created during that time?

A

Auger electrons are created by the energy released by a K-shell electron being knock out to an outer shell electron.

This knock the outer shell electron out and that is called an auger electron.

Delta rays are created with the auger or the k-electron has enough energy to go on and ionize other things.. they are whimpy and don’t mean shit.

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26
Q

Auger electrons are created mostly in what type of atom?

A

Low atomic number atoms

27
Q

What happens to the focal spot with a high mA? High kVp?

A

High mA spreads electrons out due to the amount of electrons increase… like a crowded street

High kVp - think the running down a street analogy.. the fast people run the fast they spread out…hitting the target one at a time rather than all at once. Makes the focal spot small.

28
Q

Roentgen and C/kg are used for explaining what?

A

Radiation in air

29
Q

Gray and rad are used to describe what?

A

Absorbed dose

30
Q

Sievert and rem are used to describe?

A

Effective dose (weighting factor needed and sensitivity of cells)

31
Q
  1. 1 sievert = rem? rad?
  2. 10 mSv = rem ? rad?
  3. 1 Gray = rad?
  4. 10mGy = rad?
  5. 10mSv = mGy?
A
  1. 100 rem and 100rad
  2. 1 rem and 1 rad
  3. 100 rad
  4. 1 rad
  5. 10 mGy
32
Q

3 interactions x-rays have with man?

A

Scatter

Absorbed

Pass through.

33
Q

What are the names for classical scatter and what is it?

A

Rayleigh, Coherent, Thomson

<10keV

Just pass through with minimal change in direction

Small dose to patient.

No loss of energy

34
Q

What is compton scatter dependent on?

A

Density….no Z

35
Q

Compton scatter is the major comtributor to what bad things?

A

Fog

Scatter

Occupational exposure

36
Q

When does photoelectric effect happen?

A

High Z - Z3
Low energy

37
Q

What is the difference between compton and PE?

A

PE knocks out a inner k-electon

Compton knocks out out electron.

38
Q

Why doesn’t the characteristic x-rays from PE cause scatter?

A

They are so low energy that they are absorbed by the patient = dose

39
Q

Probability of the PE?

A

Z3/energy3

40
Q

What is the k-shell energy (k-edge) for iodine? Barium?

41
Q

If you want to increase something by 15% or decrease it by 15% how do you do that?

A

80keV x 1.15 to increase

80keV x 0.85 to decrease

42
Q

What is pair production? Photodisintegration?

A

Pair production - High energy photon 1.022MeV hits the nucleus and the nuclues spits out a positron and a negatron. Positron reacts with a electron and creates two gamma rays opposite of eachother

Photodisintegration - same idea but more energy… and then an alpha particle is released.

43
Q

What does attenuation depend on?

A

Z

Beam energy

Tissue density (in compton kinda)

44
Q

What is the difference of mass attenuation and linear attentuation?

A

Mass attenation is attenation per gram of stuff - so water, ice and vapor would be the same

Linear attenuation is attenuation per unit thickness of a substance - so water, ice and vapor would be different due to the molecules being spread out.

45
Q

Linear attenuation coeffienct is related to half value layer how?

A

inversely

Linear attenuation coeffiecient goes up then half value layer goes down.

46
Q

Noise is made up of what?

A

Quantum mottle - the random nature of the x-rays

Scatter

47
Q

What decreases noise?

A

mA increase

Grid/Air gap

kVp and collimation reduce scatter or mottle but increase the other so it is a wash

48
Q

What are the three types of unsharpness that effect spatial resolution?

A

Motion

Geometric

System

49
Q

What is geometric unsharpness made of?

A

Focal spot (smaller the better)

Source to object (Farther the better - less extreme angles)

Object to detector (closer the better)

50
Q

What is the modulation transfer function measuring?

A

System unsharpness or how well a system can transfer data without fucking it up

51
Q

Detective quantum efficiency measures what?

A

How much exposure is needed for a good image from a certain system

52
Q

What is the major determinart of spatial resolution in a digital system?

A

Pixel size/pixel density/pixel pitch

Pitch is the measurement of the center of a pixel to the center of another one.

53
Q

The number of bits in a x-ray system mean what?

A

The number of gray shades that are available

Higher bits = more contrast res.

54
Q

Brightness of an image is based on what?

A

mA

30% rule… need to increase mA by 30% to see a change in the density.

55
Q

What is the difference between scintillators and photoconductors?

A

Scintillators = emit light - indirect

Photoconductors = charge straight from x-rays - direct

56
Q

What is photostimulable luminescene and where do you see it in radland?

A

Photostimulable luminscene is giving off light after being exposed to light.

CR

57
Q

Where are the liberated or free electrons trapped? what element and what is it called?

A

The conduction band

Europium

58
Q

What is the sampling pitch in CR?

A

Sampling pitch is the distance between the lasers position as it reads out the plate

Spatial resolution is dependent on this.

59
Q

What type of element is used in the scintillator for DR systems?

A

CsI crystals.

60
Q

What is the difference between a scintillator and phosphor?

A

Phosphor can store the electron and the electron coming back to the atom causes the light emission.

Scintilattor atom emits the light and therefore no storage can happen.

61
Q

What is the photoconductor for DR systems made out of?

A

Amorphous selenium. - no lateral dispersion

62
Q

Is there a difference between the read out device in direct and indirect systems?

A

No both are TFTs

63
Q

DQE is better in DDR or indirect DR?

A

DDR because you don’t have the extra step of creating light.

64
Q

DR is considered what type of system…centeralized or decenteralized? CR?

A

DR = Decenteralized

CR = Centeralized.

Physics (10 decks)

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