AEC

What are the settings typically set on when using the AEC density control?

-2, -1, +1 and +2 in increments of 25%

What are some limitations of the AEC?

Once the system has been calibrated you cannot change film screen speeds, mimimum response time may be too long for certain patients (pediatrics or uncooperative), requires constant calibration

What are the two types of AEC systems?

Phototimer and Ionization Chamber

What is the purpose of AEC as it is used in xray?

Produce xrays with optimum density by controlling the amount of radiation reaching the film. Once the prescribed amount of radiation reaches the film, radiation exposure is terminated.

How do AEC systems work?

Radiation is transmitted through the patient and converted to an electrical signal terminating the exposure

How is mA selection affected by the AEC?

Set mA as normal regardless of AEC, mA setting does not affect exposure time

What is anatomic programming or anatomically programmed radiography?

Systems with control panels depicting various anatomical structures with preprogrammed exposure factors. Used in conjuction with AEC.

How is KVP selection affected by the AEC?

No effect, use KVP the same as if you had no AEC

What is the AEC density control?

Allows the RT to select a level of density usually based on patient factors.

What is the mAs readout feature?

Control panels with AEC typically give a quick readout of the mAs used when the exposure button is depressed. Should always try to note this reading as it will provide a date base for those when manual technique must be set.

How is AEC used with digital radiography?

Enhances digital imaging by controlling amount of radiation reaching the image

Do you have to consider the patient when using AEC?

Exactly the way you do when you are not using AEC. Example, body part thickness and density plus pathology, may require you having to switch to a manual technique

How should the backup feature be set?

High enough to be greater than the exposure needed but low enough to protect the patient, standard back up time is usually 150-200% of expected exposure time

What does the ionization chamber do?

Hollow cell containing air connected to a timer circuit via an electrical wire and is located in front of the image receptor acting as an entrance. It is less sophisticated and less accurate then phototimers but more reliable and is used in most modern systems.

What is the importance of centering the anatomical part to be imaged?

Improper centering of the anatomical part can result in over or under exposure.

What is the importance of selecting the proper detector?

Improper selection will result in over or under exposure, the detector should be superimposed by the anatomical part being imaged

What is the back up time feature on the AEC and how is it used?

It is the max time xray exposure will continue when using the AEC. It can be set in time or mAs and acts as a safety mechanism protecting the patient and preventing overheating of the tube.

What is the importance of collimation when using AEC?

Just as important as without AEC. AEC can not distinguish radiation from scatter and will terminate the exposure when the theshold has been met regardless of the type of radiation that reaches the sensor.

What does the phototimer do?

Uses photomultiplier tube located behind the image receptor as an exit type. Outdated technology.

What is the importance of bucky selection when using the AEC?

You either want the table or the wall. If there is not a wall bucky then you are doing the exam table top or cross table you must deselect the bucky on the control panel otherwise it can result in an overexposed image and unnecessary patient dose

What is the most common cause of repeats when using AEC?

improprer alignment of the anatomical body part