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RAD 412 > xray system design > Flashcards

xray system design Flashcards

1
Q

what is faradays law

A

states that a current will be induced in a conductor which is exposed to a changing magnetic field

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2
Q

what is flemings right hand rule

A

thumb = force
first finger = magnetic field
=middle finger = current

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3
Q

what is electromagnetic induction

A

production of an electromotive force (emf) across an electrical conductor in a changing magnetic field. Alternating …

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4
Q

1 cycle = 1 Hz = 1 rpm

A
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5
Q

how do you transform voltage? (between 2 circuits)

A
  1. coils of wire (provide AC current flowing thru primary circuit thats wrapped around a core)
  2. magnetic flux ( induced by flow of current)
  3. magnetic flux is induced into the coil of the secondary circuit and when the number of windings on secondary side is greater than the primary, voltage increases
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6
Q

what does SST stand for

A

solid state transformers

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7
Q

why are SST’s preferable

A

using small high power, high frequency semi-conductors they are more efficient and reliable for power transformation

they can also transform AC into DC

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8
Q

what is a generator cabinet

A

cabinet that sits in xray room supplying all electrical needs

converts power circuits into low or high voltages and amperage and its a high frequency generator

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9
Q

what is a watt

A

1 volt x 1 amp

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10
Q

what 6 things are in xray tube housing and what do they do

A
  1. steel outer casing to be robust
  2. lead shielding to protect from leakage
  3. output port for primary beam
  4. insulated high-voltage cable sockets
  5. oil which insulates against electrical shock and circulates to help dissipate heat
  6. expansion bellows which disable the exposure switch when tube gets too hot
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11
Q

what is shown on the exit port of the light beam diagphragm

A

DAP dose area product

measures radiation exiting tube (not radiation reaching patient)

cGyxcm^2

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12
Q

what is on the back of the LBD

A

tube suspension, which can rotate

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13
Q

whats on the sides of the LBD

A

locks
electromagnet
switches to engage motor

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14
Q

what is the envelpe of the xray tube made of

A

borosilicate glass (pyrex) with beryllium window

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15
Q

why is the envelope made of borosilicate glass

A

heat resistant
strong
electrical insulator
radiolucent

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16
Q

what 2 main things are found in the glass envelope

A

cathode with heated filament and focusing cup

anode on a spindle

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17
Q

why do most tubes have 2 filaments

A

to give large and small focal spot

2 foci provide choice of quick exposures or high resolution

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18
Q

what are the filaments made out of?

A

thoriated tungsten

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19
Q

what amps do the filaments carry?

A

3-4 amps

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20
Q

why does the cathode have 2 electrical circuts

A

1 for high voltage current to make X-rays

2 to heat the filament and make it hot

21
Q

what does the focusing cup do

A

electrostatic ally confines electrons to keep them ready to be used

22
Q

what is the focusing cup made of

A

nickel

23
Q

how does the filament get hot

A

large CURRENT thru thin wire, thickness of wire and material cause resistance.

electrical resistance is limiting affect which gives off heat and when heated enough the wire will give electrons via thermionic emission

24
Q

what is a gridded tube/ what is its use?

A

controls the electron flow electrostatic ally by having an electronic grid on the cathode, switching from the focussing cup

25
Q

why might a focussing cup need additional electrostatic charge

A

when imaging using short and rapid exposures, need precision of switching and generating electrons

26
Q

what are the 3 different types of anodes and give examples of what they are used in

A

stationary anode (metal or mobile applications)

rotating anode (standard tube)

heavy-duty anode, ceramic envelope (angiography or CT tube)

27
Q

what are the 2 different types of anode targets used in mammography and why

A

molybdenum ( get k shell to match breast tissue)

rhodium (for higher k shell energies for thicker breasts)

28
Q

why is the target at an angle

A

to reduce apparent focal spot size and decrease unsharpness

29
Q

what is the cylinder of a stationary anode made of

A

copper

30
Q

what are the 4 things that construct an anode

A
  1. disc (tolerate heat loading) ( molybdenum)
  2. track (tolerate head loading and characteristic radiation) (tungsten-rhenium alloy)
  3. head-radiant backing (removes heat) (graphite)
  4. thin spindle (reduce heat conduction to bearings) (molybdenum)
31
Q

flemings left hand rule is used only in MOTORS

A

apply current to wire

place in external magnetic field

force perpendicular to current and magnet formed causing spinning

32
Q

magnitude of EMF induced in coil is proportional to rate of change of magnetic field

A

SO
the faster you change the magnetic field, the faster it turns

33
Q

What 3 things can make an xray classified as broken

A
  • anode is pitted and xrays to consistent
  • bearings seize
  • glass cracks and hot oil goes everywhere
34
Q

why might a xray tube break

A

-problems in manufacture

  • overheating due to either large exposures or not long enough cooling time
35
Q

what will the xray machine do when it is overheating

A

expansion due to heat connects the warning circuit

warning light on generator

beeping noise

system cuts out until it has cooled OR limits the amount of rays to complete procedure

36
Q

what 2 things does heating affect

A

size (expansion or contractions)

transfer of heat (conduction, convection radiation)

37
Q

what are the positive and negative things that heating affects in xray?

A

ADV:
- heats cathode filament
- anode expansion to expected size

DIS:
- anode over-loaded due to frequent or high mAs exposures
- LBD (light sticks on)
- bearings wear in rotor

38
Q

what are 2 ways xray machines are cooled

A

internally - via oil

externally - via air or water (chiller)

39
Q

what is the use of a collimator

A

to limit the beam

40
Q

collimation is manual or motor-drive by automatic format collimation system e.g bucky

A
41
Q

what 5 components make up the light beam diaphragm

A
  1. added filtration
  2. entrance shutters
  3. mirror
  4. light source (light field)
  5. lead shutters
42
Q

What are the ADV and DIS of having a ceiling suspended tube

A

adv:
- useful in large room for trauma, orthopaedics etc

dis:
- may not go very low if ceiling is high
- only travels along length of track in each direction
- cant be used if ceiling cant take the weight

43
Q

what are the ADV and DIS of having floor mounted tube

A

adv:
- cheaper
- can reach distance that a ceiling one would have difficulties reaching

dis:
- not as hygienic

44
Q

what is the typical ration found in a moving grid within a bucky system

A

12:1

45
Q

what dimensions are the detector that is permenantly within the wall stand and table?

A

43cm x 43cm

46
Q

what type of grids are used in integrated flat detectors

A

stationary grids

47
Q

how do digital tomography and ct differ

A

dt is simpler/ simple version of ct

48
Q
A

RAD 412 (20 decks)

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