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In a Modern AEC device, the electrical charge travels along a ____________ to a _____________
-wire
-timer circuit
If a digital IR is overexposed what will occur?
Computer adjusts image brightness
Image will have decreased contrast
Patient will be overexposed
EI number will reflect IR overexposure
If a technologist were to choose the center chamber instead of the two outside chambers for a chest X-ray, what would this cause?
A longer exposure time, increased image receptor and patient exposure, and the EI number would indicate overexposure
What is the the main purpose of the back up timer?
To limit unnecessary exposure if the AEC fails or is used improperly
How can the radiographer obtain a shorter exposure time?
increase the mA
How many radiolucent detectors are usually found in Modern AEC devices?
3-5
Failure to select the proper detectors results in what?
Improper image receptor and patient exposure, image quality
Improper centering over the selected detector produces what?
An over or under exposed image
Why is the back-up timer useful?
Limits unnecessary exposure, protects X-ray tube from excessive heat load, prevents overexposure of the patient
What is AEC minimum response time?
The shortest exposure time an AEC system can produce
What are the advantages of AEC?
-Ensures reproducible radiographic images regardless of tissue density and thickness variations
-Produces consistent images
-Improves exposure accuracy
-Decreases repeats
-Decreases patient exposure
-Increases department efficiency
If more than one AEC detector is chosen, how are the electrical signals measured?
The electrical signals from all detectors are averaged
True or false: the body part must cover the entire selected detector to obtain an optimal exposure.
What percentage higher should the back-up timer be from the time set?
150-200% higher
How long is the AEC minimum response time usually?
about 1 ms
What is quantum noise?
mottle- grainy appearance
Where should the technologist select the defectors?
From the area of interest
What does the back-up timer refer to?
The maximum length of time an exposure will continue
The back-up timer may terminate the exposure prematurely and result in underexposure of an image when:
1. Using low mA
2. Examining large patients or body parts
3. Preforming lateral or cross table exams
1 & 2 only
What patients may you need a shorter exposure time for? And Why
pediatric patients because they are smaller and have a risk of motion
If a digital IR is underexposed what will happen?
Computer adjusts image brightness
Image quality will be poor
EI number will reflect IR underexposure
Which chambers are used for a Pa chest X-ray?
The two outside chambers to lay over the lungs + heart
Today the back-up timer is automatically controlled, and must stop at____________
6 seconds or 600 mAs
When activated, what happens to the back up timer?
An alarm sounds
To obtain a longer exposure time what can the radiographer do to their technique?
decrease mA