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30 Cards in this Set
- Front
- Back
- 3rd side (hint)
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What is the shortest time you can have on a single phase circuit?
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1/120 sec
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How is kV produced?
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Autotransformer selects a predetermined amount of voltage that becomes kilovolts through the step up transformer
if you select 60v how many will you get? |
60,000 volts
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What are the 2 circuits in an x-ray circuit?
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Primary or main circuit and filament circuit
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What does a transformer do?
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Steps up or steps down voltage which also increases or decreases amperage
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Where is a rheostat and what does it do?
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It is on the filament circuit and decreases volts and increases amps What is the principle behind it?
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variable resistance
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Where is a choke coil and what does it do?
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Same as rheostat it decreases volts and increases amps.
What is the principle behind it? |
back EMF through electromagnetic self induction
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Which circuit has mA and which one has amps?
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Main or primary circuit has mA and the filament circuit has AMPS
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Which type of x-ray circuitry is the most efficient producing the most homogeneous beam?
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High frequency
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What is the most common timer in use today?
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Electronic timer
how short of a time can it produce? |
1/1000 Sec
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How does a mAs timer work?
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When the desired mAs level is reached the circuit is shut off
What is the principle behind timers? |
motor
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How does an AEC timer work and what was its predecessor?
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Automatic exposure control has replaced phototimers. phototimers had a device behind the IR that monitored exposure level while AEC has ionization chambers in front of the IR that shuts the circuit off when the proper amount of ionization is reached
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What is the modern version of a choke coil?
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Saturable reactor
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On a high frequency circuit what controls the both the frequency and amplitude of the pulses?
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An oscillator or inverter unit inverts the pulses and a ac-dc converter changes the frequency.
What frequency does it achieve and what amount of voltage ripple? |
60hz is converted to 60,000 hz with a voltage ripple of only 3-4%
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What are the 3 wires going to the filament?
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Filament circuit and high voltage circuit and ground
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Why are there 2 filaments and focal spots on a tube?
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small one is for greater detail and large ones for larger anatomical parts.
mammography and interventional studies use even smaller ones for detail |
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What is the max mA for most x-ray tubes?
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1200 mA
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What is the space charge effect?
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achieved at focusing cup; max mA is reached by the limit of negative charge that is reached between the thermionic cloud and the negative charge of the filament; no more electrons can be added
this limits tubes to 1200 mA |
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Why is tungsten chosen for filament material?
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high melting point
difficult to vaporize |
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What does the focusing cup do?
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narrows electron beam
has negative potential made of nickle |
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Where is the actual focal spot?
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On the anode where the electrons actually hit.
Where is the effective focal spot? |
On the IR
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What is saturation current?
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kVp moves entire cloud, there are no more electrons to move
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What is the angle used on the anode?
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Usually about 12 deg
what material is used and why? |
tungsten because this is where the x-rays are produced and tungsten produces x-rays within the diagnostic range
layered with rhenium to disperse heat note: mammography uses molybdeum because it uses a lower range |
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The effective focal spot is always _______ than the actual focal spot.
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The effective focal spot is always smaller than the actual focal spot.
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What rotates the anode?
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Induction motor
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What controls the size of the actual focal spot?
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the size of the filament
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What are the inherent filters on an x-ray tube?
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Glass
Oil Plastic |
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What is the speed range of rotating anodes?
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3600 to 10,000 rpm
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Why is it important to warm up the anode?
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To prevent cracking and help maintain the vacuum
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What is the allowable radiation leakage level from tube housing?
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100 mR/hr at 1 meter
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What helps tube cooling?
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dielectric oil and air fan
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