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Medical Imaging > X-ray > Flashcards

X-ray Flashcards

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USMLE® Step 1 flashcards
1
Q

principles for x-ray

A

beam of high energy electrons
interact with a target material
interact with patient tissue, some pass through
interact with image to produce grey scale

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2
Q

why is bone very absorbant

A

due to its high density and atomic no.

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3
Q

white parts of image

A

more energy absorbed

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4
Q

what is xray energy measured in

A

kVp

peak kilovolts

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5
Q

what is the role of aluminum filter

A

absorb low energy photons

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6
Q

what is the effects of a higher kVp

A

lower contrast - more grey

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7
Q

what is the effect of a lower kVp

A

high contrast

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8
Q

what is the amount of xrays measured in

A

mAs

milli amps x second

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9
Q

what is the relationship between density and absorption

A

linear

if you double density of tissue, you double absorption and scattering

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10
Q

role of image receptor

A

convert xrays energy to image

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11
Q

different types of receptor

A

film screen - chemical reaction
computed - sacnning laser
direct-direct - computing

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12
Q

how does direct - direct radiography work

A

as xrays pass through crystals, release electrons, they ionise and form current which is collected at the capacitor.
thin film tranistor is switched so the current is released

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13
Q

what should you look at to get a good image

A

amount of collimnation
centering - where the middle ray will be
limit diverging beam

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14
Q

generator

A

creates high voltage
made up of coils
primary and secondray (has more coils =higher current)
alternating current, changes direction of a magnetic field, generates voltage

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15
Q

order of electromagnetic spectrum

A 
radio 
microwaves 
infared 
ultra violet 
xrays 
gamma (highest)
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16
Q

useful characteristics of xrays

A

penetrate matter
interact with matter
can cause certain materials to fluoresce
can cause certain materials to produce electric charge

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17
Q

how are xrays generated

A

cathode produces electrons
filaments are heated, removing electrons
creates a high potenial difference between cathode and anode
electrons accelerate to anode

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18
Q

why is the glass tube in oil

A

heat disserpation

electrical insulation

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19
Q

properties of anode

A

good conductor
good heat disapator
made of tungston

20
Q

electricity

A

flow of electrons in a material and the rate of flow of electrons is a meaure of the electrical current

21
Q

potential force

A

is the ‘driving force’ which moves the electrons along a conductor, has an effect on kinetic energy, measured in kVp

22
Q

electric current

A

amount of current, determines the amount of thermionic emission, measured in milliampes mA

23
Q

3 ways which electrons collide with target

A
  1. interaction between them and outer electrons in the atom (no heat or xray)
  2. interaction between them and the nuclei of the atom (heat and xray)
  3. interaction between them and individual electron in the inner orbits (heat and xray)
24
Q

how much energy is produced as heat in xray production

A

95-99%

25
Q

bremstrahlung radiations

A

energetic electrons from the filament interact with the nuclei of target atoms and are slowed down, thus giving off energy in the form of xray

26
Q

characteristic radiations

A

energentic electrons remove electrons from the inner orbitals and the vacanies created are filled by the electrons from outer orbitals, giving off energy in the form of x-ray
closer orbital is to nucleus - higher binding energy but lower potential energy

27
Q

x-ray spectrum

A

bremsstrahlung radiations form a continous spectrum

characteristics radiations form line spectra as the shells have the same amount of discrete energy

28
Q

tungsten atomic number and melting point

A

74

3370 C

29
Q

quality of xray beam

A

measure of its penetraing power

30
Q

quanity of xray beam

A

measure of the number of photons in the beam

31
Q

why is funneling of xray important

A

saftey
only hits part of the body you want
less radiation exposure

32
Q

newtons law of conservation of energy

A

energy neither created nor desroyed, only changed in form

33
Q

why is tungsten used

A

heat stable
good electrical conductor
has alot of electrons
- positive protons in nucleus

34
Q

why does characteristic xrays have two spikes on the spectrum

A

first spike if for first shell in the atom
second spike for second shell
each has 2 spikes due to the different spin orbitals in the paired electrons in the shells

35
Q

why do we have rotating andoes

A

heat diserpation
preserves the anode
more high energy eletrons

36
Q

andoe angle

A

makes source of xray as close to point source as possible

small angle = closer to point source = more effective source

37
Q

role of filtration

A

enriches beam with high energy photons by absorbing lower energy xrays
higher average energy
- greater penetration
- reduce skin dose

38
Q

ionisation chamber

A

gas filled
a propotion of incident photons cause ioniastion which is collected at the charged anode of the chambre
measure dose area product in cG

39
Q

generators

A

cathode needs low voltage so mulitple circuits
high voltage tranformer
voltage rectifier

40
Q

what does voltage rectifier do

A

converts oscilaiting voltage to constant voltage

41
Q

intensity across the beam

A

varies because electrons travel into deeper layers of the anode, deeper they go = lower intensity
increase as angle is reduced, side closest to andoe is lower

42
Q

fine focus filament

A

smaller
used when geometric focus limit image quality
energy focused on smaller area
reduce tube loading to prevent damage

43
Q

when is the fine focus filament used

A

high detail
low patient attenutaion
extremities

44
Q

broad focus filament

A

image limited by patient attentuation
increased heat dissipation
permits higher tube loading

45
Q

when is broad focus filament used

A

less detail required
high patient attenuation
chest, abdomen, l.spine

Medical Imaging (12 decks)

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