Automatic Exposure Control/Phototiming Flashcards
What are AECs programmed to do?
Terminate radiographic exposure time
The AEC does NOT control any other exposure factors except…
The length of the exposure time
What is still under the control of the radiographer using an AEC?
mA and kVp
The AEC function is to:
_______ a ______ _______ of radiation and ____ the timer circuit when a radiation _____ of ______ quality is reached
The AEC function is to:
MEASURE a PRESET QUANTITY of radiation and BREAK the timer circuit when a radiation DOSE of SUFFICIENT quanity is reached
What are the 2 types of AECs?
- Photomultiplier
- Ionization Chamber
Which AEC is more popular?
Ionization Chamber
What does the photomultiplier consist of?
Consists of a fluorescent screen, a photomultiplier tube, and a complex electrical circuit
What is the photomultiplier connected to?
Connected to a timer designed to terminate the exposure time
Where is the photomultiplier placed?
Under the bucky tray
- a large device
- not radiolucent
With phototiming, what happens when the x-ray strikes the fluorescent screen?
It will glow
The glowing light is _____ by the ________ and is converted to __________.
The glowing light is DETECTED by the PHOTOMULTIPLIER and is converted to ELECTRICAL ENERGY.
In phototiming, the _____ passes through to the ______ to a ______, which will ______ the _____ when the ___________________ is reached.
In phototiming, the ENERGY passes through to the CIRCUIT to a CAPACITOR, which will TERMINATE the EXPOSURE when the PRE-DETERMINED ELECTRICAL CHARGE is reached.
What is the disadvantage of the phototiming system?
The cassettes cannot have lead foil so more backscatter radiation is produced which leads to fogging of the image
The ionization chamber
- must be…
- located…
- plate is…
- will…
The ionization chamber
- must be RADIOLUCENT
- located between patient and IR
- plate is only 5mm in thickness
- will reach a pre-determined charge and terminate exposure time
What is the basic design of the ionization chamber?
Ionization chambers (_____ or _____) and a complex _____________ connected to the ______ to ______ the exposure.
Ionization chambers (DETECTORS or CELLS) and a complex ELECTRICAL CIRCUIT connected to the TIMER to TERMINATE the exposure.
In ionization chambers, each chamber has ____________ separated by a _________________. These are encased within a ____________ (credit card size)
In ionization chambers, each chamber has 2 ELECTRODES separated by a THIN LAYER OF AIR. These are encased within a THIN ALUMINUM SHELL (credit card size)
With the ionization chamber, when x-rays ______ the ______ shell and their _________, ______ are released and _______ occurs.
With the ionization chamber, when x-rays PENETRATE the ALUMINUM shell and their AIR MOLECULES, ELECTRONS are released and IONIZATION occurs.
What is ionization?
Adding or removing electrons from their orbital shells
With ionization chambers, the ____ are attracted to ______ charged ________ and are carried through an _________ to a ____________.
With ionization chambers, the ELECTRONS are attracted to POSITIVELY charged ELECTRODES and are carried through an ELECTRICAL CIRCUIT to a CHARGE CAPACITOR.
A capacitor is also called a…
Condenser
What is a capacitor/condenser?
A device used to store specific quantity of electricity
With an ionization chamber, once the amount of ________ is _______, any further influx of _______ will cause the _______ to _______.
This action will ___________.
With an ionization chamber, once the amount of ELECTRICITY is STORED, any further influx of ELECTRICITY will cause the CAPACITOR to DISCHARGE.
This action will TERMINATE THE EXPOSURE.
What 6 things must radiographers select?
- Optimum kVp (least amount of radiation to penetrate patient)
- mA stations
- Density level (normally set as normal)
- Photocell, 3 (area of interest is what you select)
- Back-up timer (in case of malfunction)
- Table or vertical bucky
