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Radiology Exam 2 > Xray Machine > Flashcards

Xray Machine Flashcards

1
Q

Overall principle of an xray machine

A

Accelerate electrons towards a piece of metal in a vacuum

Electrons interact w metal = xrays

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2
Q

Function of glass tube in xray

A

creates vacuum for xray production

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3
Q

Cathode function in xray

A

generates electrons

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4
Q

anode function in xray

A

receives electrons and produces xrays

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5
Q

What is the power supply in xray machines

A

high/low voltage circuits

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6
Q

What are the components of a cathode

A

tungsten filament

focusing cup

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7
Q

Tungsten filament in cathode

A

connected to a low voltage circuit

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8
Q

Focusing cup in cathode

A

Negatively charged concave reflector

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9
Q

Functiono of tungsten filament in cathode

A

When heated - emits electron cloud

Source of electrons that will be sent to anode to produce xrays

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10
Q

Focusing cup in cathode function

A

Focusing cup electrostatically focuses the electron beam to the focal spot on anode
Electrons are repelled by the negatively charged focusing cup

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11
Q

Descibe anode in xray

A

Copper block
Tungsten focal spot = target
+ charged to attract electrons
Path from cathode to anode is the high voltage curcuit

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12
Q

What is the path from cathode to anode

A

high voltage circuit

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13
Q

Focal spot (anode)

A

Site of xray production
Small rectangular area in anode
+ charged
Attracts electron cloud from cathode

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14
Q

What 4 things should an ideal target (tungsten focal spot) have?

A
  1. High Z#
  2. High melting point
  3. High thermal conductivity
  4. Low vapor pressure at high temperature
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15
Q

Why is it advantageous to have a high Z# for an ideal target?

A

Promotes maximum conversion of electron energy to xray photon energy

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16
Q

Tungsten satisfies all requirements of an ideal target except what? How is this addressed?

A

Tungsten is a poor heat conductor

Solved by copper block and cooling oil to assist in heat dissipation

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17
Q

Why do we want a low vapor pressure at high temperature for an ideal xray target?

A

Can otherwise damage target

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18
Q

Focal spot should be _____ to assist in heat dissipation

A

large

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19
Q

Focal spot should be _____ to increase image sharpness

A

small

20
Q

What are the opposing issues regarding focal spot size?

A

Should be large to assist in heat dissipation
Should be small to increase image sharpness

SOLVED BY LINE FOCUS PRINCIPLE

21
Q

Line focus principle

A

Makes possible a large actual focal spot & “projected”/”effective” focal spot of small size
Placement of target at an angle
= better heat dissipation
= increased image sharpness

22
Q

Copper block of anode

A

Good thermal conductor
Removes heat from tungsten target
Reduces risk of melting of target

23
Q

Function of glass tube of xray machine

A

Vacuum tube

No gas to prevent collision of the electrons to the gas molecules which impair xray production

24
Q

Function of cooling oil in xray

A

dissipates heat

25
Q

Rotating anode

A

Tungsten target is a beveled disk that rotates when tube is operating
Electrons strike successive small areas of target = acheives obj of having small focal spot
Actual focal spot is the circumference of the disk = helps distribute heat over large areas
DISADVANTAGE - $$$$$

26
Q

Most dental systems use what kind of anodes?

A

stationary

bc rotating is $$$$$

27
Q

Purpose of low voltage circuit

A

Heat filament to cause thermionic emission

28
Q

How does a low voltage circuit work

A

Variable resistor increases/decreases resistance in circuit and changes current in filament
Controls # electrons produced at filament
mA control of xray machine actually adjusts this current

Increase mA = increase electrons sent to anode

29
Q

If you increase mA in a low voltage circuit, what is the result?

A

Increase electrons sent to anode

30
Q

Milliampere current (mA)

A

Electrons from heated filament to the target WITHIN the xray tube
Controls # xray photons

Increase mA for a given exposure time = increase receptor exposure

31
Q

Increase mA for a given exposure time, _____ receptor exposure

A

increase

32
Q

High voltage circuit

A

Creates high potential difference between cathode/filament and anode/target
Gives high velocity to filament electrons
Voltage varies between 50 - 100 kVp

33
Q

An increase in kVp results in a _____ in mean energy of polychomatic xray beam - ultimately influences ______

A

increase

image quality

34
Q

as kVP increases, velocity of electrons (energy) ____

A

increases

35
Q

As kVp increases, photon energy (quality, penetrability) ______

A

increases

36
Q

An increase in photon energy (quality, penetrabiity) results in…

A

Fewer photons interact in pt

Radiographic contrast decreases

37
Q

As kVp increases, # photons _____

A

increases

38
Q

An increase in the # of photons results in…

A

Increase in receptor exposure

39
Q

Autotransformer

A

Changes kVp
Located in control panel
Compensates for variations in incoming line voltage = VOLTAGE STABILIZER

40
Q

Receptor exposure

A

Measure of total xray beam exposure to the sensor
Must be enough to properly penetrate/image pt with acceptable noise levels
Must not be too much to over expose the pt (unnecessary dose) or receptor (poor image quality)

41
Q

The receptor exposure must be enough to…

A

properly penetrate/image pt with acceptable noise levels

42
Q

the receptor exposure must not be too much to…

A

over expose pt - unnecessary dose

over expose receptor - poor image quality

43
Q

How is receptor exposure controlled

A

kVp - quality, quantity
mA - quantity
Exposure time
Collimation, filtration, SID

44
Q

kVP controls…

A

receptor exposure
beam quality - image contrast
beam quantity - exposure

45
Q

For intraoral dental imaging, kVp is often set at…

A

60-70 kVp

46
Q

mA controls…

A

receptor exposure
beam quantity - exposure
Reported on xray tube control head

47
Q

How is exposure time measured

A

Seconds
Measured in pulses on older xray tubes
Related to 60 cycle alternating current (AC) incoming power supply
1 pulse - 1/60 sec
Newer machines report exposure time directly (ms)

Radiology Exam 2 (1 decks)

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