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CT Physics > Test 1 (X Ray Tube Construction) > Flashcards

Test 1 (X Ray Tube Construction) Flashcards

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1
Q

What is the input energy of an X-ray tube?

A

Electrical energy

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2
Q

What is the output energy of an X-ray tube?

A

Heat

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3
Q

What percentage of the incident energy of an X ray tube is heat?

A

99%

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4
Q

What is 1% the incident energy of an x ray tube?

A

x rays

bremsstrahlung
characteristic x rays

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5
Q

What is the housing of the x ray tube?

A

the visible part of the tube that is filled with oil

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6
Q

Where is the glass vacuum located?

A

inside the metal housing (insert)

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7
Q

Where are x rays produced in the tube?

A

Inside the glass vacuum

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8
Q

What are three disadvantages of heat production in an x ray tube?

A

limits beam intensity
limits throughput
cause of death for x ray tube

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9
Q

What are the functions of oil in the tube housing?

A

conduction of heat

electrical insulation

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10
Q

What is the purpose of bellows on the inside of the tube housing?

A

allows oil to expand when hot

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11
Q

What does the tube housing shield against?

A

high voltage

leakage radiation

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12
Q

What is the inside of the tube housing wrapped with?

A

lead

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13
Q

What is electrically special about the tube housing?

A

the tube housing is electrically grounded

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14
Q

How many filaments are usually kept inside the glass insert?

A

usually 2

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15
Q

What is thermionic emission?

A

the boiling off of electrons from the heating of the filament

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16
Q

Which part of the x ray tube is also known as the cathode?

A

the filament

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17
Q

What is the filament?

A

the source of electrons

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18
Q

What is another term for thermionic emission?

A

The Edison effect

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19
Q

How many volts are typically used to heat the filament with electrical current?

A

10 volts

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20
Q

What is the typical current of the filament?

A

3-5 amps (not the same as tube current)

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21
Q

What is the filament usually made of?

A

tungsten

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22
Q

What are the advantages of tungsten?

A

high melting point

little tendency to vaporize

long life expectancy

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23
Q

What are the disadvantages of tungsten?

A

Not as efficient at electron emission as some other materials

24
Q

2 attributes that make electrons useful in x ray production are:

A

ability to be accelerated

ability to be steered

25
Q

What kind of voltage is applied to the anode?

A

High positive voltage

26
Q

What are the two electrical requirements to produce x-rays?

A

Filament voltage

high voltage

27
Q

What is the focal spot?

A

the portion of the anode that is struck by the electron stream

28
Q

What is the place from which x-rays are emitted?

A

focal spot

29
Q

What charge does the focusing cup have?

A

negative

30
Q

What is the purpose of the focusing cup?

A

focuses the electron stream toward the anode

overcome stream’s tendency to spread due to electron repulsion

31
Q

Focal spot sizes affect and limit ________.

A

resolution

32
Q

What is the advantage of a small focal spot?

A

optimized resolution

33
Q

What is the advantage of a large focal spot?

A

improved heat rating

34
Q

The larger the focal spot, the more it will _____ place on a patient.

A

blur a tiny

35
Q

The larger the area the electron beam hits, the more _____ the beam can be without _______.

A

intense

melting the target

36
Q

A more intense beam means:

A

shorter exposures

less potential for motion

faster studies

better throughput

37
Q

Are stationary anodes used in CT?

A

No

38
Q

What is the advantage of a rotating anode?

A

spreads heat over a large area

39
Q

What is the disadvantage of a rotating anode?

A

It is very expensive because of how heavy it is (require bearings) and for electronics to control rotation

40
Q

Higher speed rotation of an anode mean:

A

more bearing wear

better heat ratings

41
Q

A larger diameter of an anode means:

A

better heat rating

and more expensive

42
Q

Are CT anodes large or small in diameter?

A

very large

43
Q

What is the target angle?

A

the angle between the imaginary line extending the target and the vertical axis

44
Q

What is the typical target angle?

A

7-15 degrees

45
Q

What is the true (actual) focal spot?

A

the focal spot seen from the filament

46
Q

What is the apparent (effective/ projected) focal spot?

A

the focal spot as seen from the patient

47
Q

What is the advantage and disadvantage of a large target angle?

A

Poorer heat rating

better field coverage

48
Q

What is the advantage and disadvantage of a small target angle?

A

optimized heat rating

limited field coverage

49
Q

A large target angle creates a _______ actual focal spot.

A

small

50
Q

A small target angle creates a _________ actual focal spot.

A

large

51
Q

What is the heel effect?

A

The intensity of the x ray beam is significantly reduced on the anode side

52
Q

Target angles affect actual, apparent, or both focal spot sizes?

A

actual only.

apparent focal spots remain the same

53
Q

CT requires long ___________ intensity exposures.

A

high

54
Q

CT requires tube heat ratings with a ______________ capacity.

A

high heat

55
Q

What auxiliary equipment is used for cooling?

A

blower

oil heat exchanger

water jacket/ heat exchanger

CT Physics (4 decks)

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