Radiography Exposure Settings Flashcards

1
Q

What does kV determine?

A

The kilovoltage applied across the tube head during the exposure and therefore the speed at which the electrons bombard the target

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2
Q

What does kV do?

A

Control quality, alter contrast

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3
Q

Why would you increase the kV?

A

For tissues which
- have a high atomic number
- have a high density
- are very thick

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4
Q

What does mA control?

A

The degree of heating of the filament which in turn affects the number of electrons produced

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5
Q

What does mA do?

A

Controls the quantity of X-rays/intensity of the X-ray beam and alters the blackening of the film

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6
Q

What does time (s) indicate?

A

Total time that the kV is applied across the tube head

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7
Q

What does time (s) determine?

A

Number of xrays

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8
Q

Increasing time (s) is equivalent to increasing what?

A

mA

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9
Q

What does the total quantity of X-rays produce depend on and what term describes this?

A

Length of exposure and mA. mAs.

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10
Q

How do you calculate mAs?

A

mA x s

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11
Q

Why should you select the largest mA instead of s even tho you can achieve the same mAs with higher seconds?

A

Risk of movement blur

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12
Q

What does kV alter?

A

Contrast of the film

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13
Q

Define contrast.

A

The difference in radio graphic density between two adjacent areas.

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14
Q

A radiograph with lots of black and white but limited grey is said to have high contrast and called …?

A

Soot and whitewash

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15
Q

A film with a wide grey scale is described as … ?

A

Flat

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16
Q

What would happen if kV is too high?

A

Dark film with few different shades of grey. Flat. Lacks contrast.

17
Q

What would happen if the kV was too low?

A

Means that the bone is under penetrated. Soot and whitewash. Contrast too high.

18
Q

What does increased kV cause in relation to tissues?

A

Increased penetration of all tissues

19
Q

Increased mA or s causes…?

A

Increased blackening of the film

20
Q

What will happen to the film if mA or S is too high?

A

Dark image, contrast between tissues still visible

21
Q

What will happen to the film if mA or s is too low?

A

Pale image

22
Q

Is there a relationship between kV and mAs? What is this relationship?

A

Technically no, but appear to be linked. If you increase kV by 10, you can halve the mAs

23
Q

What is the film focal distance?

A

Distance between the effective focal spot and film/digital receptor.

24
Q

Explain inverse square law

A

As the primary beam leaves the tube head it spreads out and its intensity decreases

25
Q

What is inverse square law formula?

A

Intensity ∝ 1
————————
Distance squared