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Biomedical Skills > Medical X-rays > Flashcards

Medical X-rays Flashcards

1
Q

What is electric charge measured in?

A

Coulombs (C)

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2
Q

1 Coulomb is the magnitude of..

A

the electrical charge in 6.24 x10^18 electrons

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3
Q

Electricity is a form of energy related to..

A

the flow of electric charges

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4
Q

Voltage equation =

A

Work done (or potential energy change) divided by charge

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5
Q

Current equation =

A

charge passing through area divided by time

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6
Q

Unit for current

A

coulomb per second or ampere (A) - shortened to amps

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7
Q

Power =

A

the rate of consumption of electrical energy

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8
Q

power unit

A

watt (W)

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9
Q

Watt equation =

A

V x A

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10
Q

Resistance of a material

A

the opposition to the passage of electric charge

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11
Q

Ohm’s law equation

A

A = V / R

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12
Q

Resistors

A

devices that resist the free flow of electric current through them

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13
Q

Transistors

A

Devices whose functions inc switching, voltage/current regulation, and amplification

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14
Q

Capacitors

A

devices which store electric charge

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15
Q

Diodes

A

Devices with low resistance to current flow in one direction, and high resistance in the other

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16
Q

Current direction

A

electrons flow from negative to positive

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17
Q

To produce x-rays

A

Inside the x-ray tube the electrons are jumping from one section to another without a wire. within the x-ray tube that x-rays are produced and emitted.

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18
Q

What’s the x-ray tube

A

essentially a massive valve, or switch, completing an electric circuit, and consists of a cathode and an anode enclosed in a vacuum.

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19
Q

Cathode

A

Negatively charged side of the x-ray tube (next to focusing cup)

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20
Q

Filament

A

Very tightly wound coil of wire (usually made of tungsten)

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21
Q

When an electric current is passed through, it heats up to such an extent that…

A

some of the electrons have enough energy to break free (thermionic emission)

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22
Q

number of electrons emitted from the filament is directly proportional to..

A

the amount of electrons flowing inside it

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23
Q

as negative electrons repel each other, the electrons that have been emitted have a tendency to..

A

spread out in different directions

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24
Q

what is a focusing cup?

A

a negatively charged housing that directs the electrons to stay together

25
Q

the force is overpowered by the repulsive force of the focusing cup and the electrons…

A

tend to converge rather than diverge

26
Q

anode

A

positively charged (so it attracts electrons)

27
Q

the anode consists of

A

a flat circular disc that acts as the target for the stream of electrons that are emitted from the cathode

28
Q

what happens when the electrons hit the anode

A

they slow down very fast and lose lots of energy very quickly

29
Q

99% of energy lost is in the form of

A

heat

30
Q

1% of energy loss is in the form of

A

X-rays through the bremsstrahlung process

31
Q

what is the bremsstrahlung process?

A

radiation produced by the deceleration of an electron passing through a nucleus

32
Q

what happens if electrons are fired through a space containing any gas?

A

electrons interact by colliding with gas molecules and producing lower secondary electrons

33
Q

why are lower secondary electrons not desirable in an x ray tube

A

as they make the quantity and quality of x-rays produced very difficult to control

34
Q

because of lower secondary electrons, x-ray tube requires…

A

a vacuum environment, maintained by an airtight glass enclosure

35
Q

what does oil do in the vacuum environment

A

cools the apparatus

36
Q

what is in the tube housing

A

oil, tube, electrical connections and a small window at the bottom

37
Q

what does the small window at the bottom of the tube housing do?

A

allows x-rays to leave

38
Q

what is tube housing lined with

A

lead

39
Q

what does the lead around the tube housing do?

A

prevent stray x-rays from escaping

40
Q

what happens when you increase the current flowing through an x-ray tube?

A

increases the number of electrons which are flowing around the circuit, so the number of x-rays generated would increase

41
Q

what happens when you increase the voltage?

A

the photons which make the x-rays will have more energy and the x-rays will be more penetrating

42
Q

whats the target area

A

the area where the x-rays hit after leaving the x-ray tube through the window

43
Q

what are the x-rays generated by

A

the anode

44
Q

where do the x-rays leave

A

a point directly above the window of the tube housing

45
Q

variable amounts of the x-ray beam that passes through body tissue depends on…

A

the composition and thickness of the tissues and the strength of the beam

46
Q

magnitude of this variation in intensity mechanism

A

x-ray beam emanating from the patient produces diagnostic info

47
Q

the info content of this x-ray image must be transformed into..

A

a visible image with minimal info loss

48
Q

the higher the kV in the x-ray tube the…

A

the more penetrating the x-rays are, although the amount of scattering increases

49
Q

the lower the kV the…

A

the less penetrating the x-rays are, although there is less scattering and thus more contrast between bone and soft tissue

50
Q

for thick body sections like the abdomen, it’s necessary to use

A

a high number of kV to allow significant radiation to pass through the patient’s body and register on the x-ray image

51
Q

for bony structures with finer detail like a and radiograph, you need

A

low kV

52
Q

what happens if you use an incorrect number of kV

A

poor quality image is produced

53
Q

amount of darkening of an x-ray image is quantified by…

A

the optical density D

54
Q

optical density equation

A

D = log i0/it

55
Q

i0 =

A

the intensity of light before it passes through the image (incident radiation)

56
Q

it =

A

the intensity of light that has passed through the image (transmitted radiation)

57
Q

a good radiograph should have optical density between

A

2 and 4

58
Q

if D < 2 then…

A

the image is too bright

59
Q

if D > 4

A

the image is too dark

Biomedical Skills (4 decks)

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