Chapter 40 Computed Tomography Patient Radiation Dose Bushong: Radiologic
Science for Technologists
MULTIPLE CHOICE
1. U.S. Public Health Service data suggests that CT examinations currently account for
approximately of total patient effective dose. a. 10%
b. 25%
c. 50%
d. 70%
ANS: D
U.S. Public Health Service data suggests that CT examinations currently account for
approximately 70% of total patient effective dose.
2. CT tissue dose is approximately the average fluoroscopic dose. a. less than
b. equal to
c. greater than
d. incomparable
ANS: B
CT tissue dose is approximately equal to the average fluoroscopic dose.
3. Because CT uses a cone-shaped x-ray beam, scatter radiation is , and
contrast resolution is .
a. reduced significantly; improved
b. reduced significantly; decreased
c. increased significantly; improved
d. increased significantly; decreased
ANS: A
Because CT uses a cone-shaped x-ray beam, scatter radiation is reduced significantly,
and contrast resolution is improved.
4. In multislice helical CT, the dose profile tail is called .
a. umbra
b. penumbra
c. vignetting
d. pin-cushion appearance
ANS: B
In multislice helical CT, the dose profile tail is called penumbra.
5. During helical CT, at a pitch of 1.0, the patient radiation dose is approximately
that of conventional CT. a. less than
b. equal to
, c. greater than
d. incomparable
ANS: B
At a pitch of 1.0 the patient radiation dose is approximately the same.
6. In CT imaging, as with radiography, patient dose is to x-ray beam intensity and
to the average beam energy.
a. proportional; directly proportional
b. not proportional; directly proportional
c. proportional; indirectly proportional
d. not proportional; indirectly proportional
ANS: A
In CT imaging, as with radiography, patient dose is proportional to x-ray beam intensity,
and it is also directly proportional to the average beam energy.
7. Most modern CT scanners are technology. a. first-generation
b. second-generation
c. third-generation
d. fourth-generation
ANS: C
Essentially all CT imaging systems today are third-generation technology.
8. The collimators define the cone beam and the collimators further reject scatter
radiation.
a. prepatient; predetector
b. predetector; prepatient
c. prepatient; postpatient
d. postpatient; predetector
ANS: A
The prepatient collimators define the cone beam and the predetector collimators further
reject scatter radiation, thereby improving image contrast.
9. The collimator that improves image contrast by limiting the amount of scatter radiation
that reaches the detector is the .
a. prepatient collimator
b. postpatient collimator
c. prepatient and postpatient collimator
d. the collimator does not serve a purpose in CT
ANS: B
The collimator that improves image contrast by limiting the amount of scatter radiation
that reaches the detector is the postpatient collimator.
Science for Technologists
MULTIPLE CHOICE
1. U.S. Public Health Service data suggests that CT examinations currently account for
approximately of total patient effective dose. a. 10%
b. 25%
c. 50%
d. 70%
ANS: D
U.S. Public Health Service data suggests that CT examinations currently account for
approximately 70% of total patient effective dose.
2. CT tissue dose is approximately the average fluoroscopic dose. a. less than
b. equal to
c. greater than
d. incomparable
ANS: B
CT tissue dose is approximately equal to the average fluoroscopic dose.
3. Because CT uses a cone-shaped x-ray beam, scatter radiation is , and
contrast resolution is .
a. reduced significantly; improved
b. reduced significantly; decreased
c. increased significantly; improved
d. increased significantly; decreased
ANS: A
Because CT uses a cone-shaped x-ray beam, scatter radiation is reduced significantly,
and contrast resolution is improved.
4. In multislice helical CT, the dose profile tail is called .
a. umbra
b. penumbra
c. vignetting
d. pin-cushion appearance
ANS: B
In multislice helical CT, the dose profile tail is called penumbra.
5. During helical CT, at a pitch of 1.0, the patient radiation dose is approximately
that of conventional CT. a. less than
b. equal to
, c. greater than
d. incomparable
ANS: B
At a pitch of 1.0 the patient radiation dose is approximately the same.
6. In CT imaging, as with radiography, patient dose is to x-ray beam intensity and
to the average beam energy.
a. proportional; directly proportional
b. not proportional; directly proportional
c. proportional; indirectly proportional
d. not proportional; indirectly proportional
ANS: A
In CT imaging, as with radiography, patient dose is proportional to x-ray beam intensity,
and it is also directly proportional to the average beam energy.
7. Most modern CT scanners are technology. a. first-generation
b. second-generation
c. third-generation
d. fourth-generation
ANS: C
Essentially all CT imaging systems today are third-generation technology.
8. The collimators define the cone beam and the collimators further reject scatter
radiation.
a. prepatient; predetector
b. predetector; prepatient
c. prepatient; postpatient
d. postpatient; predetector
ANS: A
The prepatient collimators define the cone beam and the predetector collimators further
reject scatter radiation, thereby improving image contrast.
9. The collimator that improves image contrast by limiting the amount of scatter radiation
that reaches the detector is the .
a. prepatient collimator
b. postpatient collimator
c. prepatient and postpatient collimator
d. the collimator does not serve a purpose in CT
ANS: B
The collimator that improves image contrast by limiting the amount of scatter radiation
that reaches the detector is the postpatient collimator.
