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What are the 2 types of x-ray equipment?
diagnostic and therapeutic
What are the ranges for diagnostic (mA, seconds, kVp)?
- 10-1200mA
- 0.001-10 seconds
- 25-150 kVp
For fixed a tilting model tables, what's the ranges? (3)
-90/15
-90/45
-90/90
- trendelenburg tilt
Upright receptor units support and contain what?
- supports image receptor in a vertical orientation
- contain a Bucky assembly and may include AEC
What is the line current for USA?
60 cycle
What is the line current worldwide?
50 cycle
What is the line current for a 3 phase?
440-480V
Which type of power is the most inefficient in x-ray production?
Single-phase power- b/c touches zero
This type of power is most popular and widely available
Three-phase power (High Frequency)
Describes the flow that changes direction periodically
Alternating current (AC)
Is the unidirectional flow of electric charge
Direct current (DC)
Nearly all x-ray equipment operates on?
210-220 V
What is root mean square (rms)?
Refers to the most common mathematical method of defining the effective voltage or current of an AC wave
Which phase produces 100% ripple?
Single phase
Full wave-rectification is?
The most efficient, x-ray production occurs during this portion of the voltage waveform
multi-phase power
What is the most efficient type of electrical power?
Changes AC to DC
What does a rectifier do?
Main power switch:
an on-off switch for the unit connected to the facility's power supply
Line compensator:
device usually wired to the autotransformer that automatically adjusts the power supplied to the x-ray machine to 220 volts
Circuit breakers:
Protect against shirt circuits and electric shock
Autotransformer:
an adjustable transformer controlled by the kilovolt peak (kVp) selector on the operating console
Step up transformer:
increases voltage and decreases current
Timer circuit (exposure timer):
- located in this section because it is easier to control (turn on and off) a low voltage than a very high one.
- timer circuit variations include the synchronous timer and the electronic timer
What is a synchronous timer?
Drives a shaft of 60 revolution a minute
What is an electronic timer?
Most accurate, allows for intervals as small as 1 millisecond
Autotransformer:
- requires AC to operate: to induce voltage, generates magnetic flux, inducing electricity
- turns ratio determines how much voltage is stepped up
- voltage is being induced in the secondary coil which has more wires than the primary coil
mA meter:
a device placed in the secondary circuit that monitors x-ray tube current
Rheostat/ variable resistor/ mA selector
An adjustable resistor controlled by the mA selector on the operating console
Exposure timer: AEC
Works with the rheostat; together; they determine the quantity of electrons boiled off of the filament & available for x—ray production
Step-down transformer:
used in the filament circuit to increase the current by reducing the voltage that is applied to the filament
filament step-down transformer
Responsible for changing the amps to milliamps
Focal spot selector:
Controls spatial resolution/ recorded detail, and influenced by filament
Exposure switch/ Deadman Switch:
- closes circuit, located behind control window on generator console.
- located behind control window on generator console
Single-phase generator
This generator is least efficient and produced the highest patient dose
Full wave rectified:
- 2 pulses per Hz
- 120 pulses per second
- 100% voltage ripple
Full wave rectified with 6 diodes:
-6 pulses per Hz
-360 pulses per second
-Voltage ripple 13-25 percent (little more efficient)
Full wave rectified with 12 diodes:
- 12 pulses per Hz
- 720 pulses per second
- Voltage ripple 4-10 percent
High frequency generators: AC & DC power converters and inverters
- convert 60 cycle to kilohertz (kHz)
- full-wave rectified can produce 12-13 kHz waveform
- voltage ripple 1%
- most popular am common type of generator!!
- most efficient x-ray production!!!
(IMPORTANT)
What is used to rate generator output?
power rating (VA0.7=W
Falling load generators:
- the mA starts at the highest possible setting and "falls" throughout the exposure
Electronic timers
Which timer is most sophisticated?
Milliampere-second (mAs) timers
This timer is based upon a predetermined mAs value
AEC (Automatic Exposure Controls) also knows as phototimer or Automatic Exposure Devices
These timers terminate exposure based upon a predetermined exposure value and uses an ionization chamber?
Modern minimum reaction time
- 0.001 seconds
- 1/1000
What are ionization chambers used for?
For trunk, chest, abdomen, spine.
-radiolucent at correct kVp's
-typically have 3 detector positions
Backup time circuit
This should be set at 150% of anticipated manual technique
What is the maximum exposure per U.S public law?
600 mAs
-exposures >50 kVp
