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FRCR Part 1 Physics > Fluoroscopy (Erin) > Flashcards

Fluoroscopy (Erin) Flashcards

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1
Q

The entrance surface dose should not exceed ??? mGy/min for any given field of view

A

100mGy/min

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2
Q

An anti-isowatt curve for automatic brightness control causes the kV and mA to…

A

increase in proportion with one another to maintain image brightness

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3
Q

What is the equation for brightness gain

A

Minification gain x flux gain

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4
Q

What is the equation for minification gain

A

(D input / D output)2 (where D is diameter of input and output screen respectively)

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5
Q

What is the typical number value for flux gain

A

50

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6
Q

What is the typical value number for minification gain

A

100

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7
Q

What is the input phosphor made of?

A

Sodium activated caesium iodide (CsI:Na)

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8
Q

What is the X-ray absorption efficiency of the input phosphor (%)

A

70-90%

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9
Q

What colour light photons does the input phosphor convert X-rays to?

A

Blue spectrum light photons

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10
Q

What is the photocathode made of (material)?

A

Antimony caesium (SbCs3)

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11
Q

What is the role of the photocathode?

A

Absorption of fluorescent light photons (from inout phosphor) and conversion to electrons

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12
Q

Is the input screen maintained at a positive or negative voltage with respect to the anode (output screen)

A

Negative voltage

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13
Q

What is the potential different (in kV) across the image intensifier

A

25kV

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14
Q

What is the role of focusing electrodes in the image intensifier

A

Metal rings held within the tube that are held at positive voltages with respect to the photocathode. Contains the electrons in the tube to travel along paths that lead them directly to the output screen

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15
Q

What is the output screen made from?

A

Silver activated zinc cadmium sulphide (ZnCdS:Ag)

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16
Q

What is the typical diameter of the output screen?

A

25-35mm
Around 2.5cm

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17
Q

Skin doses to patients may be reduced by… (3)

A
  1. Increasing the patient to detector distance
  2. Reduced Minification/magnification
  3. Lower/less exposures
  4. Smaller field of view
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18
Q

What are the 3 layers of the input screen in an image intensifier and how do they work?

A
  1. Input window (Aluminium)
  2. Phosphor layer of caesium iodide that converts X-rays to light and channels them
  3. Photocathode layer of antimony caesium to convert light into electrons
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19
Q

In fluoroscopy at the output stage what happens

A

The output layer is Zinc cadmium sulphide silver and it converts electrons back into light

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20
Q

Magnification improves image…? But because of this, minification gain …? And therefore dose must…?

A

Image quality
Decreases
Increase

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21
Q

Fluoroscopy artefact: describe Veiling glare

A

Spreading of signal across the field of view where it shouldn’t be, due to scattering of light within the image intensifier

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22
Q

DSA: what kind of subtraction is required from the pre contrast compared to post contrast image

A

Logarithmic subtraction

23
Q

DSA: the subtraction process has what effect on noise?

A

Increase image noise but perception of vessels is increased

24
Q

DSA: uses what kind of tube voltages?

A

Usually at least 70kVP to maximise attentuation in iodine based contrast

25
Q

What is the typical diameter of the input screen?

A

25cm

26
Q

Magnification equation involving distances?

A

Magnification = Focus-film distance / (Focus-film distance - Object-film distance)

27
Q

Increasing the focus-film distance will increase/reduce magnification?

A

Reduce

28
Q

Reducing the object to film distance will increase or reduce magnification?

A

Reduce

29
Q

What is the effect of a thicker input screen crystal on efficiency and spatial resolution?

A

Thicker crystal will be more efficient at converting X-rays to light photons
however the spatial resolution is reduced with thicker crystals

30
Q

How thick are the input screen CSI crystals?

A

5 micrometers

31
Q

What is the k edge of caesium iodide doped with sodium in the input screen

A

33 and 36 keV

32
Q

What colour of light photons are produced at the output screen

A

Green (530nm wavelength)

33
Q

How is the image between the input screen and output screen changed (in terms of orientation)?

A

Inverted
And
Flipped left to right

34
Q

Digital fluoroscopy: what happens to light photons after leaving the output screen?

A

They enter a CCD which converts the light into electrons for readout and digital conversion

35
Q

Digital fluoroscopy: read out at the CCD happens at what frame rate?

A

About 30 fps

36
Q

What is the function of the aluminium backing at the output screen?

A

Acts as a anode
Prevent light photons from leaking back into the image intensifier

37
Q

What is flux gain?

A

When a single electron has enough energy from acceleration to create many light photon in the output phosphor

38
Q

Dual energy subtraction images: how is this done?

A

Separate images taken with one being low kv and one being high kv

39
Q

What is the purpose of dual energy subtraction images?

A

To bring out bony detail usually.
Can be used the other way round too for chest imaging (remove rib detail)

40
Q

ABC is achieved by using signal from what part of the image?

A

Centre

41
Q

What is the purpose of ABC?

A

To guide adjustment of kvP and mas to maintain image brightness with different body parts

42
Q

During angiographic procedure, to maintain brightness which parameter should be increased preferentially?

A

mAs
Kv should be held at about 60 to take advantage of k edge of iodine

43
Q

A digital spot image is equivalent to how many seconds of continuous screening?

A

2 seconds

44
Q

A low dose high kv curve is useful for which group of imaging?

A

Paediatric imaging

45
Q

In a low dose high kv curve, the dose is preserved at the expense of…?

A

Image quality

46
Q

Spatial resolution in Fluoro is most limited by…

A

Light spread in output phosphor

47
Q

Spatial resolution in fluoroscopy is about…?

A

5 lp/mm

48
Q

Fluoroscopy usually uses a focal spot of size…?

A

0.6mm

49
Q

DSA: what image is subtracted from what?

A

The pre contrast mask image is subtracted from subsequent contrast runs

50
Q

What is pixel shifting?

A

A technique to reduce motion artefact in Fluoro

51
Q

The CCD array of a. Fluoroscopy unit has matrix size of…?

A

1024x1024 pixels

52
Q

Standard tube current in fluoroscopy is…?

A

2-6mA

53
Q

IN fluoroscopy, patient ESD usually increases with image intensifier field size. T/F?

A

False

54
Q

T/F- The entrance surface dose rate should ideally be less than 50mGy/min

A

True

FRCR Part 1 Physics (20 decks)

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