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Image science principles > mobile x-ray > Flashcards

mobile x-ray Flashcards

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1
Q

mobile x-ray equipment components

A 
generator 
the drive unit
weight
brakes and locks
tube support
exposure beep warning
collimator
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2
Q

mobile x-ray drive unit

A
  • either motor driven or motor assisted

- electric motor with power supplied by batteries

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3
Q

mobile x-ray weight

A
  • have consideration for lifts and manoeuvrability, counterweight in tube column to aid movement
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4
Q

mobile x-ray units

A
  • mostly for hospital use and too heavy to be carried
  • motor driven
  • exposure output is less than room based units
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5
Q

portable x-ray units

A
  • for home visits, military and veterinary work
  • can be carried and set up
  • low exposure output
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6
Q

limitations for mobile units

A
  • low power input - thus has a shorter and narrower exposure range compared to units in x-ray rooms
  • takes longer to take images that require a higher exposure
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7
Q

ideal characteristics of a mobile unit

A
  • has a DAP meter
  • has a focal point distance of 55-205 cm from the floor
  • single-phase charging - Power flows through a single conductor.
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8
Q

ideal characteristics of mobile machine (generator and x-ray tube)

A
  • mAs range - 0.1-500
  • exposure times 0.001-1.25
  • focal spot 0.3/1.0 mm
  • power 20 kW
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9
Q

ideal characteristics of a mobile machine (wireless portable detector)

A

detector sizes - 35x43cm and 24x30cm

image resolution - up to 3.4Lp/mm

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10
Q

SNR

A

Signal to noise ratio

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11
Q

weakness of a digital system

A
  • images can be viewed by clinicians immediately after x-ray has been taken
  • image may have low resolution at this point and may be used as a diagnostic image - could lead to misdiagnosis
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12
Q

disadvantages of portable units

A
  • restricted exposure factors - cannot use high kVp
  • limitation on the length of exposure time
  • Cannot use units for a long time to prevent damage
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13
Q

high frequency generator

A
  • mains AC
  • Rectifier
  • Inverter
  • high voltage transformer
  • x-ray tube
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14
Q

what does the rectifier do

A
  • converts AC to DC
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15
Q

issues with capacitor discharge mobile units

A
  • with long exposures - the kV might fall during the exposure - causing under penetration
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16
Q

problems with restricted x-ray tube movement

A
  • lack of tube height SID<180cm for CXR
  • most patients are normally supine/semi-erect, which degrades the image
  • infection control is difficult to observe
  • can damage furniture
17
Q

advantages of digital mobile x-ray

A
  • can acquire images quickly
  • however there is the temptation to ‘ just repeat’ for a better/slightly better image
  • efficient
18
Q

advantages of digital mobile x-ray

A
  • can acquire images quickly
  • however there is the temptation to ‘ just repeat’ for a better/slightly better image
  • efficient
19
Q

advantages of analogue x-ray machine

A
  • fully developed technology

- relatively inexpensive

20
Q

advantages of Digital x-ray machine

A
  • simple to store data

- low radiation exposure of patients

21
Q

disadvantages of Analogue x-ray machine

A
  • has poorer image quality compared to new digital systems

- complicated reproduction and storage of images

22
Q

disadvantages of Digtal x-ray machine

A
  • high acquisition costs

- different imaging formats makes it difficult to share

23
Q

mobile x-ray equipment components (generator)

A
  • constant potential - either mains independent, using rechargeable batteries for all functions or capacitor discharge generator
24
Q

image acquisition CR

A
  • uses a photostimulable phosphor as an image receptor
  • the phosphor absorbs the radiation, trapping electrons at energy levels vis the process of photostimulable luminescence
  • the imaging plate is then read by a laser which releases the trapped electrons returning them to their original state ready for the next exposure
25
Q

DDR image acquisition can be either….

A

Direct or Indirect

26
Q

DDR image acquisition (direct)

A
  • directly converts the absorbed x-ray into a proportionally sized electrical charge with no immediate scintillating step
  • uses amorphous selenium
27
Q

DDR image acquisition (indirect)

A
  • indirect conversion - uses a scintillator to convert x-rays to light
  • x-ray photons encounter a caesium iodide scintillator and are converted into light
  • the needle-like caesium iodide structure acts to minimise scatter
  • the light then reaches a low-noise photodiode array and is converted into an electrical charge that is read out digitally before finally sent to the image processor
28
Q

what factors affect the resultant image quality?

A
  • contrast
  • dynamic range- wider range = increased range on contrast
  • spatial resolution
  • noise
  • artefacts - leads/tubes on patient, pacemaker, movement (voluntary & non- voluntary)
  • kVp levels - too low = not enough penetration
  • focal spot size
29
Q

Signal to noise ratio

A

a measure of true signal to noise

- a lower SNR generally results in a grainy appearance to images

30
Q

what improves SNR

A

increasing mAs - however patient dose also increases

using high-quality sensors - transfers x-ray photons into light photons

Image science principles (12 decks)

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