RSAP 180 Final Exam Review

Pitting of the anode commonly occurs (LO#5)

• When the unit is not warmed up properly

• When the anode is off-focus

• With extended use

• When the kilovoltage is too high

What type of grid is typically used for mobile radiography? (LO#9)

• 5:1 parallel grid

• 8:1 focused grid

• 12:1 focused grid

• 16:1 parallel grid

Answer explanation

6:1 and 8:1 focused grids are commonly used in mobile radiography

Given the technical factors below, calculate the mAs value.

68 kVp; 50 mA and 1850 ms (LO#1)

• 925 mAs

• 9.25 mAs

• 92.5 mAs

• 82.5 mAs

Answer explanation

To calculate mAs:

mAs = mA x exposure time (s)

50 mA x 1.85 s = 92.5 mAs

As kVp increases, what happens to the amount of Compton interactions? (LO#4)

• Decreases by one quarter

• Increases

• Stays the same

• Decreases by half

Answer explanation

As kVp is increased, it increases the penetrability of the x-ray photons. This results in more x-ray photons penetrating directly through the patient and interacting with the image receptor.

As kVp increases = increases compton scattering and decreases photoelectric absorption

What is the ripple factor for a 3 phase 6 pulse generator? (LO#2)

• 3-4%

• 4-10%

• 100%

• 13-25%

Answer explanation

- Single Phase Generator:

100% ripple factor

- 3 phase 6 pulse generator: 13-25%% ripple factor. Voltage in the x-ray tube never falls below 75-87%of the kVp.

- 3 phase 12 pulse generator: 4-10% ripple factor. Voltage in the x-ray tube never falls below 90-96% of the kVp.

- High frequency generator: 1% ripple factor. Voltage in the x-ray tube never falls below 99% of the kV

The following are recommendations used for extending tube life EXCEPT: (LO#5)

• Warm up the anode following the manufacturer's recommendations

• Do not hold rotor switch unnecessarily

• Use higher - mA stations when possible

• Do not rotate the tube housing from one position to another rapidly

Answer explanation

Ideally want to use lower mA stations when possible

If you could not use a grid for some reason, and had to resort to an alternative method of reducing scatter onto an image receptor, which technique could you use? (LO#6)

• Use the Air Gap Technique

• Use the SID Placement Technique

• Place the tube closer to the patient

• Turn the tube so that anode heel effect does not compensate

What is the length of time called that is necessary for the AEC to respond to the ionization and send a signal to terminate the exposure? (LO#8)

• Back-up time

• Minimum response time

• Interrogation time

• Extinction time

What is the acceptance criteria for exposure time? (LO#10)

• +/- 10% + 5 m/s

• +/- 10% + 1 m/s

• +/- 20% +1 m/s

• +/- 20% +5 m/s

One of the principle factors that contribute to the amount of scatter produced is the irradiated material itself. What is another contributing factor? (LO#4)

• mAs

• kVp

• Image receptor

• Table components

Answer explanation

3 main factors that affect scatter:

kVp

Field size

Irradiated material (amount and atomic #)