X-ray Equipment
Describe the primary functions of the generator (power supply) portion of an x-ray system.
For a typical radiographic system and then for a mammographic system, state the general range of values that are available for the:
a. KVp
b. MA
c. exposure time
Explain what are effective (rms) voltage and current values compared to peak values. Are the 120 volts available at an electrical outlet effective or peak values?
Describe the function of each of the following components in an x-ray generator.
a. transformer
b. rectifiers
c. capacitors
d. filament supply
For each of the following types of generators describe the principles of operation and inherent differences and their general advantages.
a. single phase—half-wave rectified, full-wave rectified (2-pulse)
b. three phase—6-pulse, 12-pulse
c. high frequency
d. battery operated
On the console of some older x-ray generators, a knob must be adjusted until a pointer on a meter labeled “Line Voltage” falls at an indicated position on the meter face. Explain what is being adjusted and why.
Draw a block diagram of an x-ray generator showing the relationship of the
a. autotransformer
b. high voltage transformer
c. rectifiers
to each other. Sketch the waveform in and out of these components. Compare relative voltage and current values in and out of the high voltage transformer.
Describe how KVp is and controlled in an x-ray machine.
State the purpose of the high voltage transformer in an x-ray generator.
Describe the general function and flow of energy through a transformer.
For a transformer with a secondary-primary turns ratio of 1000 to 1, compare the output to the input in terms of:
a. voltage
b. current
c. power
Explain the function of a rectifier circuit.
Describe the basic principles of a high frequency generator and the advantages with respect to a conventional 60 Hz generator.
Draw the waveform of a 120-volt peak, 60 hertz AC potential for a time duration of 1/30 of a second. Draw a line showing the effective voltage value. Mark the period of one cycle and state its duration.
Explain why an AC voltage and current is not ideal for energizing an x-ray tube.
Describe the most desirable high voltage waveform for energizing an x-ray tube.
Choose the x-ray generator that will provide the highest x-ray beam effective energy (HVL) for the same KVp and explain why.
a. single-phase, full-wave
b. constant potential
c. single-phase, half-wave
d. three-phase, six-pulse
Diagram and compare the voltage waveform for full-wave rectified single-phase and 3-phase power.
Explain why shorter exposure times at a given KVp are possible with 3-phase power and constant potential generators compared to single-phase generators.
Compare the advantages and disadvantages of single-phase and 3-phase x-ray generators.
Draw the KV waveform for a typical capacitor storage-discharge machine.
Discuss the limitations on MAS and exposure time encountered with a capacitor storage-discharge x-ray machine.
Describe how MA is controlled in an x-ray machine.
Describe how exposure time is controlled in an x-ray machine.
Identify the factors that should be evaluated as part of a quality assurance program for x-ray generators.
Describe two methods for measuring the KV of an x-ray machine. Give advantages and disadvantages for each.
Describe how an x-ray machine timer can be checked for accuracy.
State the number of focal-spot images that should be present for a single-phase, full-wave rectified x-ray generator after a 1/10-second exposure of a single-hole spinning top? Must the top spin at a particular speed? Note: The spinning top device is an old method for checking x-ray machine timers and is not used much anymore. However, it does demonstrate an important characteristic of single-phase machines.
1. Chapter 8. The Physical Principles of Medical Imaging, 2ndEd. Perry Sprawls. Medical Physics Publishing.
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