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44 terms

Ch 6 - X-ray Circuit & Tube

STUDY
PLAY
Anatomically Programmed Radiography
What does APR stand for?
kVp Meter
Measures voltage output from the autotransformer.
Line voltage compensator
Adjusts the control or fluctuation in the electric supply.
Rheostat
mA selector
Electronic timer
A timer that is capable of producing ultrashort exposure times.
Change A/C to D/C
What is the purpose of the rectifier?
40-50%
How much can the exposure time be decreased when using three-phase x-ray equipment?
Exposure Time
What does AEC automatically vary?
Back-up timer
If the AEC fails during the exposure, what unit will terminate the exposure?
Warm up the anode; Do not make repeated exposures near the tube limits
How can you extend the x-ray tube life?
Autotransformer; Line Voltage Compensator; kVp Meter; Exposure Timer; Line Meter
Low Voltage Circuit contains:
mA selector; Rheostat, Step-down tx, Focal Spot Selector
Filament Circuit contains:
Rectifier unit; X-ray tube; Milliammeter
High voltage Circuit contains:
Serve as the kilovoltage selector
Primary purpose of the autotransformer?
Rheostat in the filament circuit
mA selector on the control panel represents what?
Diode
What is the name of the device that is used to provide rectification?
4
How many diodes are need to provide full-wave rectification?
More efficient; reduce patient dose
Advantages of high frequency generator over single or three-phase generators?
Anode begins to rotate; full heat is applied to the filament
What happens when the rotor switch is activated?
The center detector is always located in the center of the IR at the central ray.
Where is the AEC detector located on a three-detector system?
200 mA
The small focal spot is used when the mA stations below __________ mA are used?
Photo Timer
An AEC which works by a photomultiplier tubes that are sensitive to light.
Ionization Chamber
An AEC which works when a specific quantity of current has been measured in this circuit, the exposure will be terminated.
Electric ground
Absorbs or "drains off" any number of excess electric charges.
Electronic Timer
More sophisticated than synchronous timers for use with three phase and high frequency generators.
Heat Unit (HU)
Used to rate the maximum heat capacity of the anode.
kVp x mA x time
What is the formula for HU?
Control Circuit
Another name for the Low Voltage Circuit?
Varies the resistance in the circuit which permits control of the amperage circuit
What does a Rheostat do?
Synchronous Timer
Controlled by a small electric motor rotating at 60 rev/sec. each 60 impulses in the electric cycle can be used as an exposure time.
Tube Rating chart
Establishes the maximum tube capacity for a single exposure.
Falling Load Generator
Computer controlled; begin the exposure at the highest mA compatible with the desired filament/focal spot selection.
Reproducibility of exposure; mAs Reciprocity; mA and exposure time linearity.
What are the three control checks to ensure mA settings accuracy?
Larger
Bucky is a moving grid that is used when radiography of the _____________ parts of the body.
17 msec (1/60 sec)
Minimum exposure time for synchronous timers?
1 msec (0.001 sec)
Minimum exposure time for electronic timers?
Depends on the back-up timer (may be synchronous or electronic)
Minimum exposure time for automated timers?
Electronic timer
What is the most accurate timer?
+/- 5%
What is the maximum variability of the exposure timer, for times greater than 10 milliseconds?
+/- 10%
What is the maximum variability of the exposure timer, for times less than 10 milliseconds?
Manually
How is the back-up timer set?
150%
What percentage of the anticipated exposure should the back-up be set to?
Public Law 90-602
Generators must terminate the exposure at 600mAs for exposures above 50kVp and 2000 mAs for exposure below 50kVp). Primarily for mammography.
Thermionic Emission
How is heat applied to the filament?