Exposure - Automatic Exposure Control

True

True or False: APR (Anatomically Programmed Radiography) factors are not set in stone and may be overridden by the technologist?

-Prevents accidental overexposure of patient due to timer switch failure of tech error. -Reduces the chance of destroying an x-ray tube due to overloading

Two reasons to use a backup timer?

Density setting

Term used to describe a tech controlling capacitor size of the AEC?

Capacitor

Term used to describe an electrical component that temporarily stores a charge?

APR (anatomically programmed radiography)

Term used to describe exposure factors being preset when a specific body part is selected on the control panel.

Ionization

Term used to describe giving an object a charge by either giving or taking away electrons?

Additive pathology

Term used to describe pathology which makes human tissue thicker and more dense than normally seen?

Destructive pathology

Term used to describe pathology which makes human tissue thinner and less dense than normally seen?

undercutting

Term used to describe scatter causing the AEC to terminate prematurely.

-A fluorescent screen converted x-ray photons into light photons -The light photons were carried to a PMT tube by lucite tubing -The PMT converted the light photon energy into electrical energy -The electrons were sent to a capacitor that discharged when full terminating the exposure.

Give four(4) points briefly describing how the old photo-timers worked?

by removing electrons from atoms

How does x-ray ionize matter? For example the air between the two aluminum electrodes in the photo-chambers which it sends to a capacitor with a preset storage limit.

Behind the bucky

In the true photo-timers, which are obsolete, where was the fluorescent screen located?

1) AEC use requires the bucky, which increases OID 2) Use of the bucky requires increased mAs/patient dose 3) Extremity bones are small and may not fit over chamber

Three reasons to never use an AEC for small extremities?

cells/photocells Chambers/photochambers Detectors

What are five different terms used to describe ionization chambers?

-Ionization Chamber (modern) -Phototimer

What are two types of AEC to consider and which one is used today with modern x-ray systems?

Check the exposure indicator values

What can be checked to verify accuracy of AEC performance?

It stops the exposure

What does the capacitor do when the AEC chambers have filled with electrons?

AEC allows us to consistently reproduce images of uniform density regardless of part thickness or pathological condition of a patient.

What is the function of an AEC?

600 mAs

What is the maximum exposure with AEC but can and should be set lower?

150% to 200% needed for the exposre

What is the recommended AEC backup timer setting range.

The center Chamber

When the patient is correctly aligned to the AEC, the central ray will pass through which chamber (Center or lateral chambers)?

Time (seconds)

When using an AEC, the tech surrenders control of what part of the exposer?

-Patient positioning -The anatomical part to be imaged and penetrated most be placed directly over the cell(s) selected because the AEC will always deliver the correct exposure to adequately penetrate the tissue(s) that are directly over the selected AEC chamber(s).

When using an AEC, what has to be very correct? Why?

Between the patient and image receptor usually just below the grid.

Where are the AEC chambers located on a ionization chamber type AEC?