AEC continued Flashcards
What do exposure adjustments/density selectors do?
-They either extend or shoten the exposure time using AEC
-Once you reach the pre-determined amount of radiation, it will allow the exposure to continue or stop early based on the value that you have slected (+,-)
If you select a - denisty selector, what technique will it shorten?
Shortens mA-Will give you a shorter mAs
How much do density selectors increase or shorten exposure?
-Increases the time ussually by 30-50%, but can be callibrated differently
When do we use exposure adjustments/density selectors?
- Use them for high scatter situations
- Use them for really thin patients
Why would we use a density selector for thin patients? What type of density selector would we choose?
Use them for really thin patients since we are getting less scatter than the system is calibrated to see
Would use a + density selector
What is fixed mode?
- What you see is what you get
- System will not recalibrate
- Very big differences between images
What is auto mode?
- System will fix things for us
- Cannot tell the difference with different exposure adjustments
- mAs and EI value will change
When will AEC be an issue?
- If the anatomy doesnt fully cover the cell
- Not imaging in the bucky
- Bad positioning or centering
- Radiopauqe objects
Should we use AEC for an odontoid position, why or why not?
No, due to the absorption of radiation from the teeth
When doing a lateral lumbar spine with AEC, what considerations should you make?
The light may be on the table, so we should out lead sheilding on the side to absorb the scatter
If the light is not fully covering the detector, what happens to mAs?
The detector sees less radiation per unit time, so it lengthens the exposure giving us a higher mAs
In which situations would the anatomy not be fully covering the detector?
- Lateral facial bones
- Scapula
- Clavicle
- Lateral hip
What detectors should you use when imaging an abdomen?
All three AEC detectors to average out over the entire abdomen
What will absorb more radiation, lung tissue or heart tissue?
Heart tissue-more density
When doing a PA chest, what detectors should we use?
Why?
We want the detectors on the L and R side of the lung above the diaphram, because with deep inspiration, the diaphram is pushed down, and the heart is moved away from the detector.
What detector(s) should we use with a lateral chest?
Only center detector
Which abnormal situations should you NOT use AEC?
- Pneumothorax
- Lung markings/single masectomy
- Suspected cardiomegly
- Barium enema
What are some of the causes of AEC overexposure?
- Wrong bucky activated
- Needed time is less than MRT
- Density left on + setting
- Incorrect detector cell selection
- Radiopaque artifacts
- Electronic malfunction
What are the causes of AEC underexposure?
- Back-up time is less than needed exposure time and terminates early
- Density left on the - setting
- Inadequate collimation-feild size too large for body part we are doing
- Inadequate detector cell selection
What happens when using a falling load generator with AEC?
The mA drops severat times during the exposure based on the maximum heat loading capacity of the tube
What percentage of falling load should we use with AEC?
100%
What is the function of a falling load generator?
Starts the exposure with the highest mA for the selected kVp
