Mobile Imaging Review

Question 1

What are the two classifications of mobile x-ray machines?

Answer 1

• Battery operated units

- Capacitor discharge units

Question 2

(T) What are the ranges for kVp and mAs on a mobile x-ray machine?

Answer 2

• Range for kVp is 40 to 130

- Range for mAs is 0.04 to 320

Question 3

What is the total unit of power for a mobile x-ray machine?

Answer 3

Total unit power is between 15 and 25 kW

Question 4

(T) Explain the various factors of the mobile machine as it relates to speed, incline, charge, recharging and number of exposures.

Answer 4

• 2 sets of batteries (10 to 16 12 volt batteries connected in a series)
• 2.5 to 3 mph average walking speed
• Maximum incline of 7 degrees
• 10 to 15 exposures when fully charged
• 10 miles on level ground when fully charged
• 8 hours charging time if fully discharged

Question 5

(T) What are the advantages/disadvantage of the capacitor-discharge unit?

Answer 5

-Smaller size/easy to move/lighter in weight
-kVp drops constantly during length of exposure
-kVp may start @ 100 but during the
exposure drop to 80 by the end

Question 6

(T) What are the three important technical factors for mobile imaging?

Answer 6

• Grid
• Anode heel effect
• SID

Question 7

The incorrect use of a grid can result in loss of density across all or part of an image. Grid cut-off can result from 4 factors:

Answer 7

1. off-center grid
2. off-level grid
3. off-focus grid
4. upside-down grid

Question 8

(T) If a longitudinal grid tilts transversely such as when placing under a patient on a mattress, the CR forms an angle across the long axis of the grid resulting in:

Answer 8

• A lost of image density or grid cutoff
• The CR must be centered along the center axis of the grid. If the CR is off from the midline, grid cutoff can result. The more CR is off centered the greater the grid cutoff.

Question 9

What is the ratio and focal range for most focus type grids?

Answer 9

• 6:1 or 8:1 ratio

- 36 to 44” focal range

Question 10

(T) What is the grid ratio for portable and bucky grids?

Answer 10

• Portable grids: 6:1 or 8:1

- Bucky grids: 12:1

Question 11

(T) What is the concept of the anode heel effect?

Answer 11

• The intensity of radiation from the cathode end is greater than at the anode end.
• The heel effect causes a decrease in image density @ anode end due to the greater absorption of x-rays.

Question 12

(T) Anode heel effect:

Answer 12

A thicker body part @ cathode end and a thinner part @ anode end.

Question 13

(T) Mobile radiography produces:

Answer 13

the highest occupational radiation exposures for radiographers.

Question 14

(T) Recommended minimal distance from mobile unit when making exposure is:

Answer 14

6 feet or length of the cord.

Question 15

(T) The single most effective means of radiation protection is :

Answer 15

Distance

Question 16

(T) according to the Federal Safety Regulation. SSD or source-to-skin distance cannot be :

Answer 16

less than 12 inches