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Medical Imaging > Xray > Flashcards

Xray Flashcards

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USMLE® Step 1 flashcards
1
Q

Electrons in which orbital have the highest electron binding energy?

  1. K
  2. L
  3. M
  4. N
A

K Shell

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2
Q

Which of the following is not true about electromagnetic radiation?

A) They are unaffected by electric and magnetic fields

B) they cannot travel in a vacuum and need medium to travel

C) they obey duality principles

D) they have wide ranges of wavelengths and frequencies

A

B) they cannot travel in a vacuum and need medium to travel

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3
Q

X-Rays are produced by….

A) Thermionic emission

B) Acceleration of electrons

C) Deceleration of electrons

D) Elastic collisions with target atom

A

C) Deceleration of electrons

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4
Q

Which one of the following is not true?

A) x-rays are part of the EMS

B) x-rays are ionising radiation

C) x-rays are absorbed and transmitted by body tissues/organs

D) x-rays can get reflected from the body surface

A

D) x-rays can get reflected from the body surface

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5
Q

What are the knobs on the x-ray machine?

A) Collimators

B) Light beam diaphragm

C) Cathode

D) Exposure Factors

A

A) Collimators

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6
Q

What do the collimators control?

A

The exposure/projection area which the x-rays will be fired to

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7
Q

How does a focusing cup help in narrowing electron beam towards anode?

A) it generate electricity which helps its narrowing of the electron beam

B) Its negatively charged so electrons can’t scatter

C) Its positively charged so electrons are attracted to it

D) Its neutral and hence helps the narrowing of the beam

A

B) Its negatively charged so electrons can’t scatter

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8
Q

Where is the focusing cup found?

A

Between the anode and cathode in the x-ray tube

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9
Q

What is the purpose of the focusing cup?

A

To focus the electrons towards the anode and stop spatial spreading, ensuring the accuracy of the true focal area

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10
Q

Which of the following is not true about Bremsstrahlung radiation?

A) Its also called braking radiation

B) the majority of x-rays are produced in this way

C) the intensity of the x-rays produced is related to the Z (atomic number) of the target atom

D) the intensity of the x-rays produced is not released to the energy of the electron beam

A

D) the intensity of the x-rays produced is not released to the energy of the electron beam

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11
Q

Bremsstrahlung is one type of radiation, which is the other for the generation of x-rays?

A

Characteristic

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12
Q

What type of x-ray radiation is shown here?

A

Bremsstrahlung

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13
Q

Describe the characteristic spectrum properties

A
  • Different for different elements
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14
Q

You are taking an x-ray image of a femur bone, by covering the hip area on top and the knee area below.

Which side should the cathode end of the x-ray tube be placed?

A)Towards Hip area

B) Towards knee area

C) It doesn’t matter

A

A)Towards Hip area

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15
Q

Describe the anode heel effect.

Why should the cathode end of the x-ray tube be placed at the hip if imaging the femur?

A

The anode is an angle. Those which are produced twards the cathode end, are a much higher intensity than those produced in the middle of the anode loose energy and have a lower pentrating power.

The hip is much more dense, and so should absorb the more intense x-rays.

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16
Q

Mr Smith has been sent for an abdominal x-ray image, but has a BMI of 40. What radiographic technique should be applied compared to one with a normal BMI?

A) Higher KVp

B) Higher mAs

C) Higher kVp and mAs

D) A secondary grid should be used

E) All of the above

A

E) All of the above

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17
Q

You are using 80 kVp and 5 mAs for taking an x-ray image, and you need to increase the voltage to 92 kVp. Which of the following combination of exposure factors will achieve a similar exposure?

A) 92 kvp + 10 mAs

B) 92 kvp + 5 mAs

C) 92 kVp + 2.5 mAs

D) 92 kVp + 17 mAs

A

C) 92 kVp + 2.5 mAs

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18
Q

Kvp affect contrast or density?

A

Constrast

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19
Q

mAs effects contrast or intensity?

A

Intensity

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20
Q

What does the rule of constant intensity suggest?

A

If you increase the kVP by 15% and half the mAs,

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21
Q

Name the radiography acquisition system which uses a cassette and a laser reader for taking images:

A) film/screen radiography

B) computed radiography

C) Indirect radiography

D) Direct radiography

A

B) computed radiography

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22
Q

With regards to optimisation, what is windowing?

A

The process of selecting some segment of the total pixel value range, and then displaying the pixel values within that segment over the full brightness range from white to black

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23
Q

What is the function of the gaussian filter?

A) sharpens the image

B) removes the electronic noise

C) enhances the size of the image

D) increases the contrast

A

B) removes the electronic noise

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24
Q

Exposure factors/parameters determine the ——- of an x-ray.

A

Exposure factors/parameters determine the strength of an x-ray.

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25
Q

When they pass through the body (attenuation), some x-rays will be —– or ——

A

When they pass through the body (attenuation), some x-rays will be absorbed or scattered

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26
Q

Give 3 typical clincial uses for x-ray

A

X-ray images are typically used to evaluate:

  • Broken bones
  • Cavities
  • Swallowed objects
  • Lungs
  • Blood vessels
  • Breast (mammography
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27
Q

True or False: Initially, x-rays were not known to dangerous

A

True!

Initially, x-rays were not known to dangerous- but soon the link between the rays and incidence of cancer, or other diseases in the radiologists was determined.

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28
Q

What is the source of the x-rays i.e. where are they produced from

A

The source of x-rays is produced by a cathode filament which produces high speed electrons as a result of heating from a high current (thermionic emission).

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29
Q

What converts the electrons into x-rays in the x-ray tube?

A

These electrons are directed towards an anode, here they are converted to x-rays.

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30
Q

What produces the electric current, causing the heating of the cathode

A

The high voltage generator produces the electric current which causes heating of the cathode filament.

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31
Q

What are the properties of x-ray tube?

A
  • Its mobility to enable the taking of x-rays in various situations, at different angles and in different positions.
  • The x-rays produced have to be of a uniform energy to provide image contrast
  • The beam needs to be able to be collimated (changed in size) to enable imaging of various sized body parts, while providing optimisation and minimising dose.
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32
Q

What do more dense/thicker tissues require?

A

More dense/thicker tissue requires more photons/strength of the beam to give the contrast needed to determine pathology or identify different tissues.

33
Q

Absorption of beams is more likely at —— (higher/lower) energies.

A

Absorption of beams is more likely at lower energies.

34
Q

What is collimation?

A

Setting the size of the field which will be X-rayed i.e. hand vs chest.

35
Q

Do we want a smaller or larger field where possible?

A

Differently sized fields require different amounts of radiation

The smallest field is ideal as the more photons present, the greater the exposure to radiation, and more photons distorts the X-ray image.

36
Q

Why isn’t having the largest field possible beneficial?

A

the greater the exposure to radiation, and more photons distorts the X-ray image.

37
Q

Why might an xray unit being mobile be beneficial?

A

They’re mobile to allow for any injury presentation i.e. patient can remain on A&E trolley to minimise injury which may occur during transfer.

38
Q

What specifically causes the acceleration of the electrons from the cathode towards the anode?

A

When an exposure is made, this is the potential difference placed across the x-ray tube between the cathode and anode, causing the acceleration of the electrons from the cathode towards the anode.

39
Q

Which exposure factor is responsible for determining contrast

A

kVp is responsible for contrast because its energy determines how readily it travels through tissue of varying density.

40
Q

60 kVp would be a standard energy for e.g. hand x-ray, but this may be too low and energy dose for i.e. a hip x-ray.

Why?

A

‘Soft x-rays’ won’t fully penetrate tissue, and will just add to a radiation dose, not the quality of the image.

Chest or pelvis x-rays have a higher kVp i.e. 120 kVp to evenly penetrate tissues but makes differences less detailed.

41
Q

What sorts ‘soft’ photons out of the xray beam

A

X-ray machines therefore contain aluminium foil parts which sorts ‘soft’ photons out of the beam.

42
Q

Absorption process is known as ———

A

‘photoelectric absorption’

43
Q

How is mAs calculated?

A

mAs is milliamperes x seconds, so the current (number of photons) multiplied by the exposure length

This will alter the density of the image, making it lighter or darker.

44
Q

Why can the beam cause magnification of organs?

A
  • The incident beam is no longer uniform.
  • By a process of absorption, where the beam is partially absorbed by the tissues it travels through and scatter the beam has variability across its width.
  • This will depend on the tissues it has passed through.
  • As a result, the object being imaged can be magnified or distorted
45
Q

What is quantum mottling

A

Additionally, x-ray beams are more absorbed by bones, so more needed to go through the patient-

this is called quantum mottling and causes speckling on the image receptors.

46
Q

Other than deceleration, what other process is used to create x-rays

A

The electrons are negatively charged therefore, they are attracted to any point which is at a positive potential.

An electron naturally wants to be within an atom, held by the positive force of attraction of the nucleus.

This attractive force is what is used to produce x-rays

47
Q

The target material within the anode is usually ——

A

tungsten

48
Q

if an element has an atomic number of 74. Therefore, there are —— units of positive charge attracting the electrons per atom.

A

This has an atomic number of 74. Therefore, there are 74 units of positive charge attracting the electrons per atom.

49
Q

Describe the journey of an electron in the xray tube

A

c

50
Q

What type of x-ray is being described here:

When they pass close enough, they are momentarily drawn towards the orbital path around a nucleus. This change in direction converts some of their kinetic energy into a quantity of x-ray energy. A single conversion event produces an x-ray photon.

A

Brehmsstralung

51
Q

The exact value of a photon’s energy is unpredictable and can range from 100% conversion to a low indeterminate number.

A 100% conversion would give a photon energy keV numerically equal to the ——-

A

peak kilo voltage across the tube.

52
Q

If the x-ray energy is lower than the energy needed i.e. >120 KvP, then what happens

A

this will be filtered out by the aluminium in the x-ray tube, and will not be absorbed into the patient.

53
Q

What type of x-ray is being described here:

Energetic electrons remove electron from the inner orbitals and the vacancies created are filled by the electrons from outer orbitals dropping down to fill the gaps in shells. The energy loss due to energy difference in orbitals gives off energy in the form of X-rays. This only involves a small minority of electrons which bombard the target.

A

Characteristic

54
Q

The closer the electron to the nucleus, the greater the binding energy of the nucleus. This means there will be a —– potential difference and greater effect of the +ve anode.

A

lower

55
Q

Why would we prefer to use a rotating anode

A

Rotating- preferable

  • Increase heat dissipation (following e interaction)
  • Increase anode load
  • Prevents pitting/cracking of anode
56
Q

Other than a lower dose, why is the shortest time for an exposure is best

A

to prevent overloading of the tube-too much intensity = too much heat.

57
Q

Describe the anode angle

A
  • Real and Apparent (or effective) focus
  • Typically 7 – 15º but no predefined ideal angle slope
  • Effective spot ~3 X smaller than real

A smaller real focus is better as the lesser the magnification of the image, and greater the definition between organ boundaries

58
Q

Thermionic emission at the cathode is proportional to the ——

A

the filament area

59
Q

What is being described here

A

The anode heel effect

60
Q

Purpose of the anode heel effect

A

Emitted X-rays pass through different thickness of tungsten depending on angle of target. Increases as angle is reduced.

Across the beam length from the anode, there’s variation in the intensity of the x-ray, per unit.

The electrons which travel into the deeper areas of the anode loose energy due to the interaction with tungsten.

The x-ray tube would be manoeuvred so these x-rays would be over a less thick body part.

61
Q

Qualities of a fine focus beam

A
  • More detail
  • Narrower beam of electrons
  • Used when geometric factors limit image quality
  • Energy focused on small area of anode
  • Reduce tube loading to prevent damage
  • Less blurring of the edges of structure (less penumbra)
62
Q

Qualities of a broad focus

A
  • Less detail
  • Wider beam of electrons
  • More energy on the anode
  • Image limited by patient attenuation
  • Increase heat dissipation
  • Permits higher tube loading
  • More penumbra
63
Q

When might a fine focus beam be preferable

A

Fine Focus

  • High detail required
  • Low patient attenuation
  • Extremities
64
Q

When might a broad beam focus be preferable

A
  • Less detail required
  • High patient attenuation
  • Chest, Abdomen, L.Spine
65
Q

What is the purpose of a point source

A

A point source will require the x-rays are emitted from the same area. This will lead to an image which has a sharp outline and sharp structures.

Point source = smallest filament on the cathode, and smallest angle at the anode.

66
Q

How efficient is the x-ray process

A
  • 99.5% of electron energy converted to heat
  • Only a small percentage of X-rays produced exit the window
  • Of those x-rays making up the useful beam most are attenuated within the patient
67
Q

Purpose of filtration

A

Adding filtration enriches beam with high energy photons by absorbing lower energy X-rays:

‘Beam hardening’ – filtration of low energy x-ray via aluminium

68
Q

What are ionisation chambers

A
  • Gas-filled Ionisation chamber
  • Measures dose of x-ray given
  • A proportion of incident photons cause ionisation which is collected at the charged anode of the chamber
  • Measured in: Dose Area Product (DAP) in cGy.cm2
69
Q

What is the voltage of the xray generators

A
  • Required Voltage
    • 100,000 +volts
    • Constant Potential
    • DC – Direct Current
70
Q

What energy is supplied from the mains

A
  • Power from Electricity supply
  • 240 volts
  • Oscillating (50Hz)
  • AC – Alternating Current
71
Q

What converts low voltage from electric company into kilovoltage of proper waveform for x-ray generation

A

High Voltage Generator converts low voltage from electric company into kilovoltage of proper waveform for x-ray generation

72
Q

Purpose of the voltage rectifier

A
  • Converts oscillating voltage to constant voltage
  • 3-phase- minimises gaps in AC, as x-ray tube needs current in one direction
73
Q

Number of photons in an exposure

A

mAs

74
Q

Exposure Time implication of image

A
  • The length of time current is allowed to flow to anode facilitating x-ray production
  • Ideally, kept as short as possible to minimise blur from patient motion
75
Q
  • The energy of each individual photon
  • Refers to the maximum voltage applied between the cathode and anode at exposure
A

KvP

76
Q

At a Higher kVp there is ——- chance of absorption and/or scattering within the patient

A

At a Higher kVp there is lesser chance of absorption and/or scattering within the patient

77
Q
  • Fewer Compton interactions
  • Much fewer photoelectric interactions
  • More transmission through tissue

as what increases

A

As x-ray energy increases

78
Q
  • No change in Compton interactions
  • Many more photoelectric interactions
  • Less transmission through tissue

as what increases

A

As tissue atomic number increases

79
Q
  • Proportional increase in Compton interactions
  • Proportional increase in photoelectric interactions
  • Proportional decrease in transmission through tissue

As what increases

A

As tissue mass density increases

Medical Imaging (13 decks)

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