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Image Prod & Eval > Chapter 16 > Flashcards

Chapter 16 Flashcards

1
Q

What is kilovoltage?

A

The electrical force that pushes electrons across the tube

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2
Q

What are the abbreviations for kilovoltage?

A

KV or keV

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3
Q

What is placed upon a tube to get the electrons to move from the negative cathode to positive anode?

A

Potential Difference

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4
Q

How is potential difference adjusted?

A

By the technologist by their kVp selection

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5
Q

What does a greater potential difference bring about?

A

The greater the KV and measure of electrical quality and intensity

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6
Q

How is kVp based on alternating current AC measured?

A

By looking at the peak or average values as a sine wave function

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7
Q

What is tissue penetration a direct function of?

A

The average energy of the x-rays

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8
Q

What are the two ways kV must be measured?

A

Average kV or peak kV (kVp)

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9
Q

Why does Kv need to be measured as an average or peak?

A

Because the kilovoltage is constantly changing and the peak or average are the only ways to capture the measurement with movement taken into account

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10
Q

Why does Kv need to be measured as an average or peak?

A

Because the kilovoltage is constantly changing and the peak or average are the only ways to capture the measurement with movement taken into account

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11
Q

What is the function of kVp?

A

To penetrate the part and to achieve the best subject contrast in an image

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12
Q

What level should kVp be set to meet its function?

A

Optimal level (not too high or low)

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13
Q

What does an optimal level of kVp ensure for tissues?

A

That all tissues are represented at some degree

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14
Q

What is a rule of thumb for kVp?

A

To set it high enough to penetrate the part

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15
Q

What is a general rule for the relationship between kVp and mAs?

A

No amount of mAs (radiation) can compensate for insufficient kVp (penetration)

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16
Q

If kVp is low but mAs is high, what effect does it have on an image?

A

The part will not be properly penetrated and anatomical details will be missing in the image

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17
Q

What does a higher kVp provide an image with?

A

More gray levels

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18
Q

What do more gray levels (long contrast) demonstrate?

A

Demonstrates more anatomy as more tissues are able to be captured at varying degrees

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19
Q

What type of contrast is produced with higher kVp?

A

Low contrast

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20
Q

What is a minimum kVp?

A

The lowest kVp that still provides some degree of penetration through all tissues of interest

21
Q

How does higher KV affect dose?

A

Higher KV reduces dose

22
Q

What is the minimum kVp for hand, wrist and digits?

A

54 kVp

23
Q

What is the minimum kVp for elbow, forearm and foot?

A

62 kVp

24
Q

What is the minimum kVp for ankle or leg?

A

66 kVp

25
Q

What is the minimum kVp for knee, humerus, mandible and tangential skull?

A

70 kVp

26
Q

What is the minimum kVp for femur, shoulder, sinus, ribs, cervical and thoracic spines and iodine procedures?

A

76 kVp

27
Q

What is the minimum kVp for abdomen, pelvis, lumbar spine, non-grid chest, and skull?

A

80 kVp

28
Q

What is the minimum kVp for air contrast barium studies and esophagram?

A

92 kVp

29
Q

What is the minimum kVp for solid column barium studies?

A

110 kVp

30
Q

What is the minimum kVp for grid chest?

A

120 kVp

31
Q

What type of relationship exists between kVp and exposure?

A

An exponential relationship

32
Q

What is the 15% rule as it pertains to kVp and exposure?

A

An increase in 15% of kVp changes the exposure of the IR by a factor of 2

33
Q

What percent of increase does a factor 2 change create?

A

100%

34
Q

An increase in which technical factor is worse for patient exposure?

A

MAs

35
Q

How much does a 15% increase in kVp raise dose?

A

24-40%

36
Q

How would dose be affected by a 2X increase in mAs?

A

Exposure will be doubled as well which produces more exposure to the patient

37
Q

What effect does an increase in kVp have on contrast?

A

Lowers contrast

38
Q

Why has the definition of optimal kVp changed over time?

A

Because of the move from film processing to digital reconstructed images

39
Q

If there is enough kVp to penetrate the part, what will the computer do?

A

Still resolve a good image by using the algorithm

40
Q

How is optimal kVp defined now?

A

The amount that is well above the minimum required

41
Q

What happens if kVp is increased but mAs is not compensated?

A

The image will be overexposed and will be too dark

42
Q

How is an increase in kVp related to scatter?

A

As kVp increase more scatter will appear

43
Q

How would scatter impact an image?

A

Produce fog on an image which changes contrast

44
Q

Where does scatter radiation originate from within the body?

A

Primarily from large body parts where a large focal spot is used

45
Q

What is the significance of the origin of scatter as it pertains to kVp?

A

Since its produced from large body part and focal size, it means that kVp is not responsible directly for scatter

46
Q

If higher kVp is used on a smaller body part using a smaller focal spot how will scatter be affected?

A

The scatter will increase but not substantially enough to affect the overall image

47
Q

How do changes in kVp affect spatial resolution?

A

They do not affect it

48
Q

How much change in KV will produce a significant increase in exposure intensity?

A

4KV change

Image Prod & Eval (10 decks)

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