Factors controlling the X-ray beam intensity Flashcards

1
Q

Intensity:

A

Total amount of energy contained in the x-ray beam

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2
Q

Intensity: equation

A

Quantity X Quality

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3
Q

o Quantity:

A

Number of photons in the beam. Primarily related to tube current and exposure
time and less so by tube voltage (kVp)

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4
Q

Quantity
Expressed as:

A

tube current (mA) X time (sec) → mAs

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5
Q

oQuality:

A

Average energy the x-ray beam.

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6
Q

Quality
▪ Controlled primarily by the

A

tube voltage (kVp)

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7
Q

X-ray of beam is —.

A

heterogeneous

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8
Q

Factors
controlling the X-ray beam
intensity (6)

A
  1. Tube voltage
  2. Exposure time
    3.Tube current
  3. Filtration
    5.Collimation
  4. Source-receptor distance
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9
Q

As tube voltage increases:
(3)

A

o Number of photons generated increases
(increased quantity)
o Mean energy of photons increases
(increased quality)
o Maximum energy of photons increases

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10
Q

As exposure time increases:
(3)

A

o Number of photons generated increases
(increased quantity)
o Mean energy of photons is unchanged
(quality unchanged)
o Maximum energy of photons is unchanged
(quality unchanged)

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11
Q

As mA increases:
(3)

A

o Number of photons generated increases
(increased quantity)
o Mean energy of photons is unchanged (quality
unchanged)
o Maximum energy of photons is unchanged
(quality unchanged)

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12
Q

Filtration
Selectively removes

A

long wavelength (low energy) x-rays.

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13
Q

Total Filtration =

A

inherent filtration + added filtration

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14
Q

Inherent Filtration
(4)

A

o Glass envelope
o Immersion oil
o Metal housing
o Tube window

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15
Q

Added Filtration
(1)

A

o Aluminum disks

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16
Q

As filtration increases:
(3)

A

o Number of photons decreases (reduced quantity)
o Mean energy of photons increases (increased
quality)
o Maximum energy of photons is unchanged

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17
Q

Collimation
Restricts the

A

size and shape of the beam.

18
Q

Collimation
(3)

A

o Number of photons decreases
o Mean energy of photons is unchanged
o Maximum energy of photons is unchanged

19
Q

Inverse Square Law

A

Intensity of the beam varies inversely to the square of the source-to-receptor distance.

20
Q

Inverse Square Law
One method of calculating the new beam intensity when changing the source-toreceptor distance:
If distance is doubled (8” to 16”) =
If distance is tripled (4” to 12”) =
If distance is halved (16” to 8”) =

A

new intensity will be ¼ (inverse of 22)
new intensity will be 1/9 (inverse of 32)
new intensity will be 4x (inverse of 1/22)

21
Q

As source-to-receptor distance increases:
(3)

A

o Number of photons decreases (decreased quantity)
o Mean energy of photons is unchanged
(unchanged quality)
o Maximum energy of photons is unchanged

22
Q

Increase in: Tube Voltage (kVp)
Quantity:
Quality:

A

increase
increase

23
Q

Increase in: Tube current (mA)
Quantity:
Quality:

A

increase
no change

24
Q

Increase in: Exposure time (s)
Quantity:
Quality:

A

increase
no change

25
Increase in: mAs Quantity: Quality:
increase no change
26
Increase in: Distance Quantity: Quality:
decrease no change
27
Increase in: Filtration Quantity: Quality:
decrease increase
28
DENSITY – altered by factors affecting --- of the beam
Quantity
29
CONTRAST – altered by factors affecting --- of the beam
Quality
30
Amount of blackness of an image → Related to
how many x-rays reach the receptor
31
Density o Primarily controlled by ---, and less so by ---
mAs kVp
32
Primarily controlled by mAs, and less so by kVp Why?
Because increasing mAs and kVp will increase the quantity. Increasing quantity more x-rays will reach the receptor → the darker the image will be (higher density)
33
mAs rule:
mA and exposure time are inversely proportional.
34
If mA is increased, exposure time must be --- to maintain the same density of the image.
decreased
35
oIf mA is decreased, exposure time must be --- to maintain the same density of the image.
increased
36
Example: The mA has been increased from 5 to 10. In order to keep the same density in this image, the exposure time should be reduced from 6 to _____
?
37
Contrast
o The difference in densities between light and dark regions of a radiograph
38
Contrast is o Primarily controlled by the
voltage
39
High Contrast (Short Gray Scale) (2)
▪ Low kVp (long wavelengths, less penetrating) ▪ Density differences between adjacent areas are greater; fewer shades of gray.
40
Low Contrast (Long Gray Scale) (2)
▪ High kVp (short wavelengths, more penetrating) ▪ Density differences between adjacent areas are more subtle; more shades of gray
41
Effect of kVp on contrast Low kVp: High kVp:
High contrast (low gray scale) Low contrast (large gray scale)