Chap 11 Flashcards
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?
216mR
Focal spot size is determined by
cathode filament size
The distance between the x-ray focal spot and the object being imaged is the
SOD
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?
. 5 mAs @ 80 kVp.
Exposure factors with higher kVp and lower mAs reduce radiation exposure to the patient.
If a radiographic image has to be repeated because of an exposure error, the mAs must be changed by a factor of at least
2
When the intensities of radiation exiting the patient are very similar, the resulting radiographic image has
. low contrast
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?
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.
If the magnification factor is 1.25, the image is ______________ than the object.
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.
Which of the following is true regarding the effect of mAs on the brightness of a digital image
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).
Increasing tube filtration
increases the beam energy and decreases radiographic contrast
In maintaining the same mAs, there is a(n) ________________ relationship between mA and exposure time
inverse
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?
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
To adjust the kVp to produce the desired contrast level, the kVp must first be
high enough to penetrate the part
Which of the following is the correct formula to determine how mAs should be adjusted when different ratio grids are used?
mAs1/mAs2 = grid conversion factor1/grid conversion factor2.
Which of the following is the correct formula for the direct square law formula
mAs1/mAs2 = (SID1)2/(SID2)2.
Which of the following has an effect on how much mAs is used for a specific examination?
- generator type.
- pathologic conditions present.
- a patient’s age.
What is the relationship between kVp and subject contrast
high kVp creates low subject contrast
Which of the following statements is true regarding practices to minimize patient exposure
None of these.
To maintain the same exposure to the IR, if the SID is increased, the mAs must be
Increase
The ________________ body habitus accounts for approximately 50% of the adult population.
sthenic
If 8 mAs produces an appropriate exposure to the IR with a single-phase generator, a three-phase generator should
use lower mAs
A compensating filter
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
Too little remnant radiation caused by low kVp results in a digital image in which
the image brightness appears appropriate and quantum noise is visible
With digital imaging, if the image receptor is not exposed to enough radiation
the image brightness will appear appropriate
Given 40 mAs, doubling the mA produces the same result as
doubling the time of exposure and doubling the mAs
Increasing the kVp has what affect on wavelength and frequency?
decreases wavelength and increases frequency
If the intensity of radiation at 72 inches is 225 mR, what is the intensity if the SID is decreased to 40 inches?
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.
Changes in the SID will affect:
- Image receptor exposure
- Spatial resolution
- Magnification
image receptor exposure, spatial resolution, and magnification
Imaging a thicker body part will result in a radiographic image with
- lower contrast
- increased magnification
- more exposure to IR
lower contrast and increased magnification only
What type of relationship does kVp have with exposure to the image receptor (IR)?
direct
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?
. 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
Which of the following exposure factors produces the same amount of remnant radiation as does 20 mAs at 70 kVp?
10 mAs @ 81 kVp and 40 mAs @ 60 kVp
What type of relationship does mAs have with the quantity of x-rays produced?
Correctd. Direct proportional
Standard radiographic x-ray tubes have small focal spots that measure approximately
0.5–0.6 mm
Whenever magnification is increased
spatial resolution is decreased
Increasing the kVp by 15% has the same effect as
doubling the mAs
What mA should be selected to produce 32 mAs using a 0.04 exposure time?
800 mA.
If mAs = mA × seconds, mA = mAs/seconds, or 32/.04, which equals 800 mA
To maintain the same amount of radiation reaching the IR, if the kVp is increased by 15% the mAs needs to
be halved
The only factor that affects exposure to the image receptor, size distortion, and image contrast is
OID
OID is the only factor that affects exposure to the image receptor, size distortion, and image contrast
Standard radiographic x-ray tubes have large focal spots that measure approximately
1–1.2 mm
