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Radiology year 4 Flashcards

(65 cards)

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1
Q

What is an atom?

A

An uncharged particle with equal numbers of protons and electrons

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2
Q

What may happen if energy is supplied to an atom? And what is the process called?

A

An electron may be ejected from a shell, resulting in a free negatively charged electron and a positive ion. Ionisation

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3
Q

What is the atomic number (Z) of an element/ atom?

A

the total number of protons in the nucleus

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4
Q

What is the mass number (A) of an element/ atom?

A

The number of protons and neutrons.

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5
Q

What type of wavelength, frequency and energy do x-rays have?

A

Short wavelength, high frequency, high energy

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6
Q

What is the equation for the energy of radiation?

A

E=h(constant)f

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7
Q

What are the main characteristics of all members of the electomagnetic spectrum?

A

they do not require a medium to travel, they travel in straight lines, all travel at constant speed (3x10^8), they are not deflected by magnetic or electric fields.

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8
Q

what is a small packet of x-ray energy known as?

A

photons.

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9
Q

How are x-rays produced?

A

When high speed electrons are slowed or stopped by a target.

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10
Q

What is required to produce x-rays?

A

a source of electrons, a means of accelerating and a target

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11
Q

What happens when negatively charged electrons approach the target?

A

They are slowed or stopped by attraction towards the positvely charged nuclei within it.

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12
Q

What happens when electrons decelerate?

A

They lose energy.

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13
Q

When electrons decelerate, what proportion of the energy released is heat and what x-rays?

A

1% x-rays and 99% heat.

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14
Q

What does the x-ray machine consist of?

A

an evacuated glass envelope within an oil bath inside a lead-lined box.

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15
Q

What is the source of the electrons and what is it made of?

A

coiled wire filament made of tungsten.

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16
Q

What is thermionic emission?

A

When the coiled wire heats up, it emits loosely bound outer orbital electrons

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17
Q

Why is tungesten suitable material for the filament?

A

strong, ductile, high atomic number and melting point.

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18
Q

What is the purpose of the focusing cup?

A

it is around the filament and focuses the electorons into a single stream rather than a cloud.

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19
Q

What is the tube current?

A

The number of electrons hitting the target. It is determined by the temp to which the cathode is heated and the length of time the electrons are accelerated across the tube. It is thus measured in mAs

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20
Q

How are the electrons accelerated across the tube~?

A

By the potential difference between the cathode and anode. Normally 45-110kV

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21
Q

What is the target made of and why?

A

Tugsten. effective at stopping electrons thus more efficient xray production and high mealting point and specific heat capacity to deal with high levels of heat.

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22
Q

What proportion of energy will become an x-ray when an electron is A) completely stopped by the nucleus or b) slowed

A

a) 100% b) <100%

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23
Q

What two sub-spectra is an x-ray beam made up of?

A

continuous radiation and characteristic radiation

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24
Q

What is photon energy measured in?

A

kloelectron-volts

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25
What is continuous radiation?
when an incident electron passes near the nucleus, it slows and loses energy, which is emitted as x-rays. The energy of the x-ray is proportional to how close the electron passed to the nucleus. Max energy released when electrons collide with the nucleus.
26
What is characteristic radiation?
When an electron collides with an inner shell electron, the electron is ejected and an electron from the next shell drops in to replaceit. Energy is emitted equal to the difference in energy states.
27
What is filtration and why is it important?
When soft radiation (low energy photons) are removed by aluminium filter (2-2.5m) as this radiation is too low energy to reach the film (and therefore does not contribute to image formation) and is damaging.
28
What is the line focus principle for and how does it work?
It is used to prevent overheating of the target. The target is mounted at an angle (6-20 degrees) so that the actual focal point (the area of the target bombarded by the electrons) is muych larger than the effective focal spot (the area of the target from which the xrays are produced)
29
What does the focus principle result in?
reduced distortion of the final image and prevention of target overheating.
30
how big is the actual focal spot compared to the effective focal spot?
actual is around 3 times bigger
31
Which machines have fine and coarse focus filaments?
Larger ones.
32
What is the fine focus and coarse focus filament used for?
Fine focus: produces a fine electorn beam and a small focal spot Coarse focus filament: large electron beam and focal spot
33
When is the fine focus filament used next to the coarse focus?
fine: low exposures. Coarse: produces a less detailed image but can be used at higher exposures (used for thicker regions).
34
What are the two main types of tube design?
the stationary anode and the rotating anode tube
35
What is the stationary anode?
The filament and the target are in a line, with the target anode mounted on a copper stem to allow conduction of the heat away from the taget, where it is dissipated via cooling fins into the oil bath. The oil bath acts as both a heat sink and an electrical insulator.
36
What is the rotating anode?
Use in larger machines with high output. This has a disc with a bevelled edge of the target material opposite opposite the filament, which rotates at up to 1000rpm during exposure. This provides a continually changing actual focal spot, which again reduces overheating. The target is mounted on a molybdenum rod to prevent conduction of heat towards the moror rotating the disc, as this would cause burnout. Heat is lost via radiation direct to the oil bath.
37
What are the tube rating charts and what are they for?
They give the maximum safe combinations of kv, mAs and exposure to avoid overheating.
38
What is the quality of the beam?
the strength of the beam needed to pass through the body
39
what is the intensity of the beam?
number of beams passing through?
40
What does increasing kV setting do?
increases electron acceleration, velocity and energy, increased penetrating power
41
what does changing the target material to one with a higher atomic number do?
increases the efficiencey of xray production, increases intensity
42
what does increasing the film focal distance do?
reduces the intensity of the beam by the inverse square law
43
what does increasing filtration do?
increases the energy and quality of the beam and reduces the intensity
44
what does rectification do?
increases the average kV being applied to the tube and thus increases quality and intensity.
45
what does the tube do?
produce xrays
46
What do the transformers do and what types are there?
alter the voltage of the mains supply (240volts) to provide the appropriate supply to each circuit in the machine. Autotransformer, step-down and step-up transformers
47
what are transformets composed of?
wire coils wrapped around and iron core
48
what is an autotransformer?
provides a steady voltage to the machine to avoid uneven xray production
49
what is a step-down transformer?
low ension transformer- on the filament circuit which converst the incoming power supply of 240V to 10V to heat the filament
50
What is a step-up transformer?
high-tension transformer. Supplies the potential difference across the tube (40-100kV).
51
What do rectifiers do?
allow the current to flow in one direction only (mains supply is alternating, convert to direct)
52
What type of rectification is there?
self-rectification, half-wave rectification, full-wave rectification, three phase rectification and constant potential rectification.
53
what is self-rectification?
simplest- on smallest/ cheapest machines. X-ray tube itself acts as the diode. Electrons only flow for 50% of the time, creating xray output pulsations. Longer exposure times are required for same output (2x) and if the anode overheats, a reverse tube current could flow.
54
What is half-wave rectification?
two diodes- current only for 50% of time but no reverse tube currents possible so safer
55
What is full-wave rectifiication?
four diodes involved arranged in bridge circuit. Electron flow all the time but current still pulsitile. Xray output still pulsatile thus out[ut inconsistent and radiographs inaccurate at short exposure times.
56
What is three phase rectification?
6 diodes so that there are three cycles 120 degrees out of phase with each other resulting in an almost steady current with hust a slight ripple
57
what is constant potential rectification?
four diodes and two condensers. The condensers continually charge and discharge to create a constant tube current.
58
Do equine and small animal vets usually use horiizontal or vertical beams?
small animal:vertical, equine: horizontal.
59
What should be on the control panel?
on/off switch, line voltage compensator, milliamperage control, kilovoltage control, timer and exposure button
60
Why is it more useful to increase mA rather than s when trying to increase mAs?
increasing s may introduce a blur.
61
what type of timer should be used?
Electronic (not clockwork)
62
how long should the cable at least be that has the exposure button on the end?
2m
63
what type of machines are most often found in practises?
portable
64
Why are mobile machines not suitable near conscious horses?
cannot easily be moved out of the way of danger and cannot get close enough to the floor to radiograph the distal limb of the horse.
65
which machines are most powerful?
fixed machines

Radiology (7 decks)

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