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Medical Imaging > Projection Radiography > Flashcards

Projection Radiography Flashcards

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USMLE® Step 1 flashcards
1
Q

What are X-rays?

A

Form of electro magnetic radiation (EM)

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2
Q

What is the main difference between EM radiation?

A

Different energy levels of individual photons which is related to wavelength/frequency of photons

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3
Q

What are 4 examples of EM radiation?

A

light
radiant heat
microwaves
radio-waves

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4
Q

What length do wavelengths become visisble?

A

10^-6

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5
Q

What is the wavelength of X-ray & gamma ray?

A

x ray = 10^-10
gamma = 10^-12

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6
Q

When does ionization occur?

A

If radiation with sufficent energy can remove electrons from their shells

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7
Q

Why happens if ionization occurs in humans cells?

A

DNA could be directly damaged or indirectly by formation of free radicals/harmful substances

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8
Q

Why is indirect damage to DNA thought to more damaging?

A

water is more abundant than DNA

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9
Q

Who invented the Crookes tube?

A

Dr. Wilhelm Conrad Roentgen

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10
Q

What are 5 charcteristics of X-rays?

A

invisible
electrically neutral
no mass
travel at speed of light in a vacuum
cannot be optically focused

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11
Q

When are x-rays produced?

A

When rapidly moving electrons that have been accelerated through a potential difference of order 1kV to 1MV strikes a metal target

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12
Q

What are the 3 steps of x-ray production?

A
  1. electrons from hot filament are accelerated onto a target anode
  2. electrons are decelerated on impact & kinetic energy is converted to EM energy
  3. photons produced will have a range of energies (polychromatic)
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13
Q

How much of the energy is converted into x-radiation during the production of x-rays?

A

Less than 1% - rest is converted into internal energy

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14
Q

How is radiation attenuated when it passes through matter?

A

by absorption & scattering

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15
Q

What does attenuation result in?

A

Reduction in intensity of incident radiation beam

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16
Q

What does absorption result in?

A

Transfer of energy from x-ray photon to atoms of material

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17
Q

What does scattering involve?

A

photon deflection from its original course

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18
Q

How do x-rays form the radiographic image?

A

some tissues attenuate more photons than others & therefore beam exiting patient is more intense in some places

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19
Q

What captures the image?

A

An image receptor reacts to x-ray photons
areas of receptor that are subject to more radiation gain more signal (darker on image)

20
Q

What is photoelectric absoprtion?

A

Incident photon interacts with inner shell electron & is completely absorbed
Atomic No (Z)

21
Q

What is compton scattering?

A

interaction between incident photon and outer shell electron & ejects the electron which results in a change in direction

22
Q

What is beam attenuation?

A

Beam emitted from patient contains radiologically significant info to make a diagnosis

23
Q

What are 4 factors that affect amount & type of attenuation?

A

atomic no. of tissue
density of tissue
tissue thickness
energy of x-ray beam

24
Q

Does air have a higher atomic no. than fat or muscle?

A

Yes but it has lower density

25
Q

What does the fewer absorption of photons by air allow for?

A

More photons to reach the image receptor creating a greater image receptor exposure

26
Q

How does fat compare to muscle?

A

Lower atomic no. and density

27
Q

Why is muscle easy to distinguish?

A

Greater attenuator of the beam (increased absorption)

28
Q

What is the greatest absorber of photons?

A

Bone

29
Q

What are 2 examples of high density contrast agents?

A

Barium
iodine

30
Q

What 4 ways are contrast agents administered?

A

orally
rectally
intra-venous
intra-arterial

31
Q

What does fluroscopy involve?

A

Taking multiple low-dose x-ray images in succession to create a real-time “video”

32
Q

What are 3 scenarios that fluoroscopy is used?

A

Theatre
GI system
specialized application

33
Q

What happens if radiation exceeds threshold level?

A

Tissue function will be compromised due to cell death beyond what the tissue can cope with

34
Q

What are 4 reactions that can occur depending on exposure?

A

Skin reddening
Opacity of lens of the eye
Permanent sterility
ARS

35
Q

What is the severity of the effects proportional to?

A

Dose recieved over the threshold

36
Q

What are stochastic effects?

A

Damage to cell’s DNA -> somatic or genetic

37
Q

Is there a threshold below which no effects occur?

A

No

38
Q

What 4 thinsg does legislation include protection for?

A

patients
staff
unborn
members of public

39
Q

What are the 3 pillars pf reducing radiation risk?

A

Justification - benefit outweighs risk
Optimisation - technical & procedural steps can optimize doses
Dose limitation - legal limits exist for staff, public and unborn children

40
Q

What are 3 ways to optimise staff dose?

A

Less time spent near sources
Greater distance from source
Behind shielding

41
Q

What are 3 pros of convential radiography?

A

Accessible
Fast
Cost effective

42
Q

What are 4 cons of conventional radiography

A

Limited detail on soft tissue organs
limited detection of early diagnosis in bones disease
non-specific findings
2D

43
Q

What are 5 clinical applications?

A

Chest radiography
Skeletal trauma imaging
imaging for exclusion
follow up
SPA imaging

44
Q

How can projection radiography assess skeletal trauma?

A

Presence/absence/complexity of fracture/dislocation
relationship of bony fragments

45
Q

What are 3 signs of fracture?

A

Disrupted cortical outlines
Radiolucent lines
misalignment of bony fragments

46
Q

What are 2 fractures associated with SPA?

A

bucket handle
classic metaphyseal handle

Medical Imaging (10 decks)

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