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Radiographic Physics & Imaging > Final Study Guide > Flashcards

Final Study Guide Flashcards

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1
Q

Space charge

A

Cloud of electrons emitted from the filament before they are accelerated to the anode.

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2
Q

Motor

A

Device that converts electrical energy to mechanical energy.

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3
Q

Generator

A

Device that converts mechanical energy to electrical energy by electromagnetic conduction.

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4
Q

Falling load generator

A

With a falling load generator, the exposure time is set at a minimum.

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5
Q

Line voltage compensator

A

Measures voltage provided to the X-ray imaging system & adjusts it to precisely 240 volts.

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6
Q

Variable resistor

A

allows for finer control over current by changing the amount of resistance.

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7
Q

REsistance

A

Opposition to the flow of current.

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8
Q

Stator

A

Stationary electromagnets arranged around the outside of the tube, which induces the rotation of the rotor.

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9
Q

Capacitor

A

Device capable of accumulating and storing and electrical charge.

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10
Q

Thermionic emission

A

The boiling off of electrons at filament of X-ray tube.

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11
Q

Current

A

Electricity in motion.

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12
Q

Voltage

A

The amount of potential energy between two points in a circuit.

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13
Q

Exposure switch (what does it do?)

A

Remote control switch that permits current to flow through the circuit.

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14
Q

Step up vs. step down transformer (voltage vs current)

A

Step up transformer increases kVp and decreases amperage. Step down transformer decreases kVp and increase amperage.

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15
Q

Filament circuit provides:

A

the incoming line power to produce thermionic emission from filament of X-ray tube.

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16
Q

Rheostat

A

A type of variable resistor.

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17
Q

Space charge compensator

A

Automatically lowers the filament current to just the right amount as the kVp is raised.

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18
Q

Ammeter

A

Measures current

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19
Q

Voltmeter

A

Measures voltage.

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20
Q

Advantages of 3 phase equipment

A

3 phase is most efficient.
3 phase 6 pulse produces 35% more photon energy.
3 phase, 12 pulse produces 40% more photon energy.

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21
Q

Disadvantages of 3 phase equipment.

A

The initial cost.

22
Q

Types of transformers and descriptions (4)

A

Air core - two coils side by side.
Open core - Iron core inserted into coil intensifies magnetic flux.
Closed core - coils wound around a square or circular iron ring.
Shell type - laminated core, windings of primary and secondary coil around same core.

23
Q

Most efficient type of transformer:

A

Shell type.

24
Q

Ohm’s law

A

V=IR

25
Q

Turns Ratio

A

Ns/Np = Vs/Vp = Ip/Is

26
Q

Power formula

A

P=IV

27
Q

Causes of power loss in transformers

A

Copper losses, Eddy currents, Hysteresis

28
Q

Types of timers.

A

Synchronous timers.
Electronic Timers.
mAs timers.
AEC.

29
Q

Electronic Timers.

A

Most exposure timers are electronic and are controlled by a microprocessor.

30
Q

mAs timers.

A

Terminates the exposure when the desired mAs value is attained. Used on falling-load and capacitor discharge imaging systems.

31
Q

AEC

A

Automatic Exposure Control. Uses ionization chambers, positioned between the patient and the IR, to terminate the exposure when the appropriate charge has been reached.

32
Q

Uses of spinning top:

A

For single phase generators a spinning top test is used to test timer.
For three phase or high frequency generators a synchronized spinning top test is used.

33
Q

What comprises the high voltage generator (look at picture and notes in powerpoint.)

A

High voltage transformer
Filament transformer
Rectifiers

34
Q

What is the turns ratio in a high voltage transformer?

A

Between 500:1 and 1000:1.

35
Q

Parts of the control panel you would operate:

A

mA, kV, time and exposure switch.

36
Q

Commutator ring vs. slip rings

A

Commutator rings are on direct current generators and slip rings are on alternating current generators.

37
Q

Voltage necessary for X-ray equipment:

A

240 V

38
Q

Types of induction:

A

Self induction and mutual induction.

39
Q

Where is self-induction used?

A

In the low voltage auto transformer.

40
Q

Where is mutual induction used?

A

In the high voltage transformer.

41
Q

How many pulses per second in a half wave and full wave rectified circuit?

A

Half wave = 60 pulses per second.

Full wave = 120 pulses per second.

42
Q

Disadvantages of half-wave rectified circuits

A

Wastes half the supply of power, requires twice the exposure time,

43
Q

Voltage ripple:

A

Single phase has power has 100% voltage ripple. The voltage varies from zero to its maximum value. Three-phase, six pulse power produces voltage with only approx. 14% ripple, three phase, twelve pulse = 4% and high frequency produces a 1% voltage ripple.

44
Q

Types of rectifiers

A

Valve tubes or vacuum tubes (used in older X-ray imaging systems)
Solid state rectifiers (replaced valve tubes, made of silicon which is a semi-conductor type, and they are in use today.)

45
Q

Number of rectifiers needed for each type of power.

A

Half wave rectified circuits contain zero, one, or two diodes.
Full-wave rectified circuits contain at least four diodes.

46
Q

Backup timer

A

On an AEC…the electronic timer should be set to 1.5 times the expected exposure time as a backup timer in case the AEC fails to terminate. Many units automatically set this precaution.

47
Q

Synchronous spinning top

A

Used for 3 phase or high frequency
xray production is constant
Therefore solid line or arc appears instead of dots
Arc is measured and inserted into equation: Actual time = arc size/360.

48
Q

How a spinning top tests timer accuracy:

A

Emits X-rays in pulses. Each pulse creates a dot.
Half wave rectification: Number of dots = exposure time x 60. Ex: 0.05 secs x 60 = 3 dots.
Full wave rectification: Number of dots = exposure time x 120. Ex: 0.05 secs x 120 = 6 dots

49
Q

Minimum response time

A

All AEC have a minimum reaction or minimum response time. This is the length of time necessary for the AEC to respond to the radiation and for the generator to terminate the exposure. When AEC can’t terminate quickly enough a manual time is used. Modern AEC have a MRT of 0.001 second.

50
Q

Photomultiplier tubes

A

PM tubes are considered exit type devices since detectors are positioned behind the cassette and radiation must exit cassette before it is measured by detectors.

51
Q

Ionization chambers

A

Flat, parallel plate ionization chamber is positioned between pt and IR. Considered entrance-type detectors are positioned in front of the cassette. Radiation interacts with detectors before interacting with the image receptor.

52
Q

Amperage and voltage needed for filament circuit:

A

3-6 amps, 4-12 volts. The power to heat the X-ray tube filament is provided by filament transformer. Voltage for the filament circuit comes from the autotransformer.

Radiographic Physics & Imaging (15 decks)

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