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Rad Physics > Chap 11 > Flashcards

Chap 11 Flashcards

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1
Q

If the intensity of radiation at 36 inches SID is 600 mR, what is the intensity if the distance is increased to 60 inches SID?

A

216mR

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2
Q

Focal spot size is determined by

A

cathode filament size

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3
Q

The distance between the x-ray focal spot and the object being imaged is the

A

SOD

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4
Q

Assuming that all of these produce a similar amount of exit radiation, which of the following exposure factors minimize the radiation dose to the patient?

A

. 5 mAs @ 80 kVp.

Exposure factors with higher kVp and lower mAs reduce radiation exposure to the patient.

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5
Q

If a radiographic image has to be repeated because of an exposure error, the mAs must be changed by a factor of at least

A

2

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6
Q

When the intensities of radiation exiting the patient are very similar, the resulting radiographic image has

A

. low contrast

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7
Q

If a small adult’s 24-cm thick abdomen requires 20 mAs to produce the appropriate level of radiation reaching the IR, how much mAs should be used with a larger patient whose abdomen measures 32 cm?

A

80 mAs

For every 4–5 cm the mAs needs to be doubled, so if the patient measures 28 cm, then 40 mAs is needed. Adding another 4 cm of thickness (to get to 32 cm) requires a doubling of 40 mAs to get to 80 mAs.

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8
Q

If the magnification factor is 1.25, the image is ______________ than the object.

A

25% larger

A MF of 1.25 indicates that the image is 25% larger than the object. The image can never be smaller than the object.

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9
Q

Which of the following is true regarding the effect of mAs on the brightness of a digital image

A

mAs does not affect brightness in a digital image

The mAs does not have a direct effect on image brightness. During computer processing, image brightness is maintained when the mAs is too low or too high (within reason).

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10
Q

Increasing tube filtration

A

increases the beam energy and decreases radiographic contrast

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11
Q

In maintaining the same mAs, there is a(n) ________________ relationship between mA and exposure time

A

inverse

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12
Q

If 12 mAs produce appropriate IR exposure at 36 inches SID, how much mAs is needed at 72 inches SID to maintain that amount of exposure to the IR?

A

48 mAs

If the SID is increased by a factor of 2 (doubled), the beam intensity will be one fourth (1/22) of the original, requiring a 4´ increase in mAs to maintain IR exposure

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13
Q

To adjust the kVp to produce the desired contrast level, the kVp must first be

A

high enough to penetrate the part

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14
Q

Which of the following is the correct formula to determine how mAs should be adjusted when different ratio grids are used?

A

mAs1/mAs2 = grid conversion factor1/grid conversion factor2.

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15
Q

Which of the following is the correct formula for the direct square law formula

A

mAs1/mAs2 = (SID1)2/(SID2)2.

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16
Q

Which of the following has an effect on how much mAs is used for a specific examination?

A
  1. generator type.
  2. pathologic conditions present.
  3. a patient’s age.
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17
Q

What is the relationship between kVp and subject contrast

A

high kVp creates low subject contrast

18
Q

Which of the following statements is true regarding practices to minimize patient exposure

A

None of these.

19
Q

To maintain the same exposure to the IR, if the SID is increased, the mAs must be

A

Increase

20
Q

The ________________ body habitus accounts for approximately 50% of the adult population.

A

sthenic

21
Q

If 8 mAs produces an appropriate exposure to the IR with a single-phase generator, a three-phase generator should

A

use lower mAs

22
Q

A compensating filter

A

is used for specific anatomic areas
b. produces a more uniform exposure to the IR
c. requires an increase in mAs
Correctd. all of these

23
Q

Too little remnant radiation caused by low kVp results in a digital image in which

A

the image brightness appears appropriate and quantum noise is visible

24
Q

With digital imaging, if the image receptor is not exposed to enough radiation

A

the image brightness will appear appropriate

25
Q

Given 40 mAs, doubling the mA produces the same result as

A

doubling the time of exposure and doubling the mAs

26
Q

Increasing the kVp has what affect on wavelength and frequency?

A

decreases wavelength and increases frequency

27
Q

If the intensity of radiation at 72 inches is 225 mR, what is the intensity if the SID is decreased to 40 inches?

A

Before actually calculating the answer, it is important to think through that decreasing the distance results in increased intensity. Using the inverse square formula, I1/I2 = (D2)2/(D1)2, 225/X = 402/722, X = 729 mR.

28
Q

Changes in the SID will affect:

  1. Image receptor exposure
  2. Spatial resolution
  3. Magnification
A

image receptor exposure, spatial resolution, and magnification

29
Q

Imaging a thicker body part will result in a radiographic image with

  1. lower contrast
  2. increased magnification
  3. more exposure to IR
A

lower contrast and increased magnification only

30
Q

What type of relationship does kVp have with exposure to the image receptor (IR)?

A

direct

31
Q

200 mA @ 80 ms (0.08 s) produces 16 mAs. Which of the following exposure factors maintains 16 mAs while using a shorter exposure time?

A

. 400 mA @ 0.04 s.

By doubling the mA and halving the seconds, 400 mA @ 0.04 s equals 16 mAs while shortening the exposure time

32
Q

Which of the following exposure factors produces the same amount of remnant radiation as does 20 mAs at 70 kVp?

A

10 mAs @ 81 kVp and 40 mAs @ 60 kVp

33
Q

What type of relationship does mAs have with the quantity of x-rays produced?

A

Correctd. Direct proportional

34
Q

Standard radiographic x-ray tubes have small focal spots that measure approximately

A

0.5–0.6 mm

35
Q

Whenever magnification is increased

A

spatial resolution is decreased

36
Q

Increasing the kVp by 15% has the same effect as

A

doubling the mAs

37
Q

What mA should be selected to produce 32 mAs using a 0.04 exposure time?

A

800 mA.

If mAs = mA × seconds, mA = mAs/seconds, or 32/.04, which equals 800 mA

38
Q

To maintain the same amount of radiation reaching the IR, if the kVp is increased by 15% the mAs needs to

A

be halved

39
Q

The only factor that affects exposure to the image receptor, size distortion, and image contrast is

A

OID

OID is the only factor that affects exposure to the image receptor, size distortion, and image contrast

40
Q

Standard radiographic x-ray tubes have large focal spots that measure approximately

A

1–1.2 mm

Rad Physics (4 decks)

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