Chapter 13 Exam Flashcards
Automatic exposure control (AEC) devices work by measuring _____.
a. Attenuation of primary radiation by the patient
b. Radiation that exits the patient
c. Radiation that is absorbed by the patient
d. Radiation exiting the tube
b. Radiation that exits the patient
Which of the following exposure system operates by ionizing air that creates an electrical charge?
a. Anatomically programed technique
b. Phototimer
c. Ionization chamber
d. Non of the above
c. Ionization chamber
During operation of the AEC device, the time of exposure:
a. Is inversely related to the intensity of the exit radiation
b. Is directly related to the intensity of the exit radiation
c. Has an inverse squared relationship to the exit radiation
d. Has no relationship to the intensity of the exit radiation
b. Is directly related to the intensity of the exit radiation
What factors are important when using automatic exposure control (AEC) devices?
1. Detector selection
2. Centering part to detector
3. Back-up mAs, if set
a. 1 and 2 only
b. 1 and 3 only
c. 2 and 3 only
d. 1, 2, and 3
d. 1, 2, and 3
Increasing patient thickness while using an AEC device would result in:
a. Increased exposure time
b. Decreased brightness
c. decreased mAs readout
d. Increased image contrast
a. Increased exposure time
Which detector or combination is best for a right hip?
a. Center
b. Left
c. Right
d. Right and left
a. Center
Which is the primary goal of exposure technique charts?
a. Extend life of x-ray tube
b. Improve radiographer’s accuracy
c. Consistency in image quality
d. Increase patient work flow
c. Consistency in image quality
What type of exposure technique system uses a fixed mAs regardless of patient thickness?
a. Fixed kVp
b. Variable kVp
c. Preprogrammed
d. AEC
b. Variable kVp
Of the following, which is most important when using a technique chart?
a. Same radiographer revises chart
b. Same chart used for all x-ray tubes
c. Accurately measured patient
d. Include a patient history
c. Accurately measured patient
An advantage of the variable kVp technique chart is that it:
a. Produces lower contrast images
b. Reduces patient exposure
c. Makes a 2 kVp change sufficient with any kVp
d. Makes smaller technique changes possible
d. Makes smaller technique changes possible
Which of the following special considerations may require a decrease in mAs?
a. Bariatric patient
b. Soft tissue examination
c. Pediatric patient
d. b and c only
d. b and c only
Which of the following special considerations may require an increase in mAs?
a. Contrast media
b. Bariatric patient
c. Tissue edema
d. All of the above
d. All of the above
a system used to consistently control the amount of radiation reaching the image receptor by terminating the length of exposure
automatic exposure control (AEC)
Why do we have an AEC?
to control the amount of radiation reaching the IR
How does the AEC work?
Once a predetermined amount of radiation is transmitted through a patient, the x-ray exposure is terminated. This determines the exposure the exposure time and therefore the total amount of radiation exposure to the image receptor
What is the AEC system good at?
producing consistent levels of exposure when used properly
What are the two types of AEC?
- Phototimers: first generation of AEC systems
- Ionization chambers: more common today
Use a fluorescent screen and a device that converts light to electricity
phototimer
an electronic device that converts visible light energy into electrical energy
Photomultiplier (PM) tube
How many AEC detectors are the norm?
Most AEC systems use a set of three radiation-measuring detectors
What is an Ionization Chamber?
A hollow cell that contains air and is connected to the timer circuit via an electrical wire
- When exposed to radiation, the air in the chambers becomes ionized, creating an electrical charge
- The charge travels along the wire to the timer circuit, which trips the timer
Entrance-type devices AEC
What happens when x-ray photons interact with the ionization chamber?
the air inside the chamber becomes ionized, creating an electrical charge. This charge travels along the wire to the timer circuit. The timer is tripped and the radiographic exposure is terminated when a sufficiently large charge has been received.
- Refers to the shortest exposure time that the system can produce
- This can be a problem with some segments of the patient population, such as pediatric patients and uncooperative patients
Minimum response (exposure) time