Collimators and Grids Flashcards

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1
Q

What is the use of wedge filters in x-ray filtration?

A

produce uniform density image, if tissue is thicker on one side (e.g. breast?)

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2
Q

Functions of added filtration in x-ray production?

A
  • lowers patient dose (removes unwanted low energy x-rays)
  • change beam spectrum (e.g. optimise for mammography/ paeds)
  • remove useless high energy x-rays
  • change density of x-rays as needed (depending on tissue to be images)
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3
Q

Metric to measure filtration of x-ray

A

Half-Value Layer

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4
Q

Unit for Half Value Layer

A

mm Aluminium

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5
Q

What are compensating filters used for in x-ray production?

A

Decrease total radiation dose by decreasing x-ray intensity to thinner areas of tissue

(e.g. trough filter for chest x-ray)

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6
Q

Metric(s) to measure anti-scatter grid performance?

A

Contrast Improvement (CIF)

Bucky Factor (BF)

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7
Q

What are the two basic categories of anti-scatter grids?

A

Stationary Grids

moving Grids

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8
Q

What are filtration grids normally made of?

A

Lead, with aluminium or plastic in between

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9
Q

What is ‘Grid Frequency’ in anti-scatter x-ray grids?

A

The number of lines/cm of grid strips.

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10
Q

Benefits/ negatives of high grid frequency, in x-ray filtration grids?

A
  • less distinct grid lines,

- more radiation dose

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11
Q

What are the 2x2 types of anti-scatter grids (based on construction/ alignment)

A

Linear

  • parallel
  • focussed

Crossed

  • parallel
  • focussed
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12
Q

What is the downside of PARALLEL x-ray filtration grid?

A

cut-off of x-rays near the edge of the image (as they are coming in at an angle from the source)

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13
Q

What is the difference between parallel/ focused x-ray filtration grids?

A

Parallel grids: the grid stripes are all parallel and go straight up vertically.

Focused grids: the strips are pointed towards a focal point (where the x-rays come from),

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14
Q

What is the downside of FOCUSED x-ray filtration grid?

A

need to be careful with distance from x-ray source

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15
Q

What is ‘Grid Ratio’ in x-ray filtration grids?

A

Ratio of the height of the strips to the width of the gaps at the central line

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16
Q

What is ‘Contrast improvement Ratio’ in x-ray filtration grids?

A

Ratio of the transmission of primary radiation to the transmission of total radiation

17
Q

What is ‘Grid Exposure Factor’ in x-ray filtration grids?

A

Ratio of total radiation without the anti-scatter grid to with the anti-scatter grid

18
Q

What is ‘Strip Number’ in x-ray filtration grids?

A

strips/ cm

19
Q

What is ‘Grid focusing distance in x-ray filtration grids?

A

Distance between the front of a focused grid and the line formed by the converging planes which include the attenuating lamella of the grid

20
Q

What is ‘Contrast Improvement Factor’ (CIF) in x-ray filtration grids?

A

image contrast with/ without grid

radiographic contrast with grid) / (radiographic contrast without grid

21
Q

What is ‘Bucky Factor’ (BF) in x-ray filtration grids?

A

increase in dose associated with the use of grid

22
Q

Calculation of ‘Grid Ratio’

in x-ray filtration grids

A

height of grid/ thickness of interspace material

23
Q

Good/ Bad of high Grid Ratio?

in x-ray filtration grids

A

– are more effective
– are more expensive
– deliver higher dose

24
Q

What is ‘Bucky Factor’ also known as?

A

Grid Factor

25
Q

What is ‘Selectivity’ in x-ray filtration grids?

A

(primary radiation after grid)
______________________
(scatter radiation after grid)

26
Q

What is ‘Grid Cut-off’ in x-ray filtration grids?

A

undesirable absorption of primary radiation by the grid

27
Q

What is the ‘Air Gap Technique’

in x-ray scatter reduction

A

the patient is deliberately moved away from the image receptor.

Reduces scatter