What is Automatic Exposure Control (AEC)?
Automatic termination off the X-ray exposure
How does AEC work?
Radiation detectors below the table are used to determine the amount of radiation striking the cassette
What do AEC systems convert?
X-rays detected into electrical signal
How do the detectors work in AEC?
The detectors receive the sign and send a signal to cutoff the exposure after a pre-set amount of radiation has been received
What are the benefits of AEC?
Increase the consistency of exposure and reduce the need for repeats
What effect does changing exposure factors in AEC have on the image?
Increasing mA will reduce the exposure time and help control motion
What do modern phototiming systems use?
A three field detection system which can be selected in any combination based on the exam being conducted
Where are the detectors located and what are they made of?
Located in front of the grid and made out of aluminum
What phototiming system do Fluoro units use?
Single field system
What are the two main components of of using AEC, to ensure it’s done properly?
- Choosing the correct cells
- Properly aligning to the selected cells
What happens if the patient is no positioned on the cell correctly?
The exposure will terminate prematurely causing insufficient exposure
What does an image that is under exposure reflect?
More noise and increased contrast (high contrast)
What are the density controls in AEC?
They control the length of the exposure and can be made higher or lower based on the techs selection
What is the range of density controls in AEC?
-2 to normal to +2
How does each increase in density using AEC affect exposure?
Each step should be calibrated to produce a 25% increase in the length of the exposure
How does changing the MAs or KV affect the density setting in AEC?
It has no affect on
What is a back-up timer?
A manual or automatic internal timer that automatically terminates the exposure if the phototimer circuit fails
What is a common used AEC detector?
A gas ion chamber with a double plate of aluminum with gas encased in it
What is the first step of the AEC detector?
The chamber endures a current when gas atoms are ionized and pulled towards a positively changed anode plate
What is the second step of the AEC detector?
The charge accumulates in the capacitor, where the threshold is set, and the thyratron releases the charge to activate an electro magnate
What happens once the electromagnet is activated in AEC?
It pulls open the exposure switch stopping the exposure
Why does a backup timer need to be set in an AEC circuit?
To limit the exposure to the patient in case the circuit fails
What should the backup timer be set to in an AEC circuit?
Never more than 2 times the expected exposure
How is the exposure adjusted in an AEC circuit?
Using the density controls which adjust the sensitivity of the Thyratron up or down
-
Visual Qualities of an Image25
-
Geometric Qualities of an Image22
-
Factors Affecting Radiographic Quality134
-
Technique Charts40
-
AEC34
-
Creating the Digital Image53
-
Image Identification5
-
Criteria For Image Eval17
-
Image receptors21
-
Conventional Fluoroscopy38
-
Digital Fluoroscopy19
-
Imaging Processing & Display95
-
Quality Control33
