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RD1037 > dynamic image recording (fluro) > Flashcards

dynamic image recording (fluro) Flashcards

1
Q

what is fluoroscopy?

A

real time ‘dynamic’ x-ray images

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2
Q

who was fluoroscopy invented by?

A

thomas edison

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3
Q

when does luminescence occur?

A

occurs when materials absorb energy and emit light

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4
Q

two categories of luminescence

A
  • fluorescence - light emitted very quickly
  • phosphorescence - light emitted more slowly
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5
Q

when in radiography is fluoroscopy used?

A

when images should be sharp

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6
Q

what type of imaging does fluoroscopy use?

A

continuous ‘real time’ imaging
- low continuous x-ray exposures (0.5mA - 2mA)

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7
Q

what is fluorography

A

can select on machine the function to give a still image with HIGH resolution

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8
Q

image intensifiers

A

older way of obtaining fluoroscopy and fluorography

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9
Q

pros of image intensifiers

A

reduces patient dose by amplifying image signal

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10
Q

cons of image intensifiers

A
  • image noise
  • loss of sharp image
  • image distortions
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11
Q

what is image noise

A
  • signal that comes from anything apart form anatomy of patient
  • noise present in all electronic systems
  • appears as irregular granular pattern
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12
Q

examples of general fluoro procedures

A
  • gastrointestinal studies
  • angiography of vessels
  • micturating cystograms
  • proctograms
  • HSG
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13
Q

examples of interventional fluoroscopy procedures

A
  • angioplasty
  • stenting
  • embolization
  • biopsy
  • drainage
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14
Q

how does an image intensifier work in a fluoroscopic chain

A

Electronic vacuum
- convents remnant beam —> light
- light —> electrons
- electrons —> back to light
- increases light intensity in the process

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15
Q

5 components of fluoroscopic chain

A
  • x-ray tube
  • collimators
  • filtration
  • patient table
  • anti-scatter grid
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16
Q

what is the patient table made up of and why

A

carbon fibre
- strong enough to hold patient with minimal radiation absorption

17
Q

where is the image intensifier position

A

the intensifier usually above table

18
Q

what does an image intensifier include?

A
  • input phosphor and photocathode
  • electrostatic focusing lens
  • accelerating anode
  • output phosphor
19
Q

how much kV to accelerate electrons in image intensifier

A

25-35 kV

20
Q

what does an input phosphor do?

A

converts x-ray photons to (blue) light photons

21
Q

what is an input phosphor made of

A

fine caesium iodide crystals (CsI) - high X-ray absorption rate

22
Q

what does thicker layers help achieve

A

improved efficiency - 60% of X-ray energy converted to light

23
Q

what does a photocathode do

A

converts blue light photon energy to energy possessed by released electrons

24
Q

why is the photocathode curved

A

so that all electrons travel the same distance to output phosphor

25
Q

what is a photocathode made of

A

made of Sb.Cs (antimony and caesium)

26
Q

what is the purpose of negatively charged focusing electrodes

A

repel electron stream steering them to output phosphor

27
Q

what is the potential difference across the vacuum in an image intensifier

A

25-35kV = accelerates electrons as they pick up kinetic energy

28
Q

where is the anode located in the image intensifier

A

at the neck - +ve charged to provide a stream of electrons at constant velocity

29
Q

what does the output phosphor have a thin layer of and why

A
  • aluminium
  • prevent light travelling back to input phosphore
30
Q

what is output phosphor made of

A
  • zinc cadmium sulphide
  • converts electron energy into green light
31
Q

describe the process of flux gain

A
  • converting x-ray photon energy to many light photons
  • converting light photons to energy gained by electrons
  • electrons emitted from cathode - accelerate + gain kE
  • converts electron energy to light photons
  • gives 100x increase in brightness
32
Q

describe the process of minification gain

A
  • output phosphor is smaller than input phosphor
  • reduction in actual image size (minification) = same number of electrons concentrated on smaller surface area
  • results in a 100x brighter image
33
Q

what is the intensifiers ability to increase the brightness of image is called

A

flux gain x minification gain
(brightness gain or conversion factor)

34
Q

what is exposure factors in fluoroscopy controlled by

A

ABC (automatic brightness control)
- automatically adjusts kVp + mA
- achieved by monitoring brightness of output phosphor intensity
- ensure brightness of image at monitor is constant

35
Q

how to adjust magnification in an image intensifier

A
  • achieved by increasing the voltage to focusing electrodes
  • focuses down electron beam by electrostatic repulsion
  • so only electrons from centre portion of photocathode interact with output phosphor
36
Q

what reduces brightness

A

only central part of photocathode provides electrons to output phosphor

37
Q

how does ABC contribute to compensate in reduce brightness

A

may automatically increase radiation dose

RD1037 (8 decks)

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