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Science and Technology 1 > Introduction To MRI > Flashcards

Introduction To MRI Flashcards

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1
Q

What is a magnetic field?

A

A region of space where magnetic forced are experienced

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2
Q

What is the strength of a magnetic field field measured in?

A

Teslas

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3
Q

How many Teslas are most scanners?

A

1.5 Teslas, but scanners can be different strengths

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4
Q

What is the direction of a magnetic field represented as?

A

The letter B

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5
Q

What does the MRI scanner work on?

A

The hydrogen atoms in the body

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6
Q

What is a magnetic moment?

A

A quantity that represents the direction and strength of a magnetic field

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7
Q

The stronger the magnetic field strength, the … the magnetic moment

A

Stronger

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8
Q

Why is the direction of magnetic moments important?

A

It shows us how the magnetic moment will align with the magnetic field

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9
Q

What are the features of an MRI magnet?
(4)

A

It requires a very strong magnetic field

This is achieved using a superconducting electromagnet (the scanner is a big electromagnet)

The electromagnet is configured using wire in the shape of a coil, and then current is passed through the wire, which induces a really high magnetic field

It’s deeper than a CT scanner and has a more narrow bore (hole)

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10
Q

Why does the MRI magnet use an electromagnet?

A

So that it can produce a really high magnetic field strength

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11
Q

What are the features of the superconducting magnet?
(4)

A

High resistance increases the temperature of the coil

So it’s cooled to a low temperature in order to operate

The MRI scanner is cooled with liquid helium via a pump

The magnet is always on

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12
Q

What is the sound that’s heard in the MRI room?

A

It’s the sound of the pump pumping the liquid helium into the MRI scanner

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13
Q

What do radiofrequency transmitter coils do?

A

They produce a radio frequency pulse that’s administered to the patient in order to produce an image (this causes the loud noise that patients can hear whilst in the MRI scanner)

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14
Q

Where are the radiofrequency coils located?

A

Within the main magnet

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15
Q

Label the components of an MRI scanner:

A
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16
Q

What do surface coils do?

A

They receive the MRI signal. They’re designed specifically for certain areas

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17
Q

Where do surface coils need to be placed?
(2)

A

Over the area to be imaged

As close to the patient as possible

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18
Q

Label the control room of MRI:

A
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19
Q

Why is a button needed in MRI?

A

It quenches the magnet. If there’s an emergency, the magnetic field can be reduced by pressing the button

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20
Q

Why is a phone needed in MRI?

A

In case a patient crashes

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21
Q

Why is a microphone needed in MRI?

A

So the radiographer can talk to the patient if need be, since they’re in the CT scanner for so long

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22
Q

Why is a screen needed in MRI?

A

It’s connected to a camera on the boar of the scanner so that we can watch the patient, as they’re in there for a while

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23
Q

What needs to have happened in order for a person to be allowed to enter the MR environment?

A

The person needs to have a safety questionnaire to ensure that they’re safe to be in there

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24
Q

What are the 2 types of areas in MRI?

A

Controlled access area

MRI environment

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25
Q

What rooms include the controlled access area?
(3)

A

Control room

Scanning room

MRI equipment room

(Access to these areas are restricted)

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26
Q

What rooms include the MRI environment?

A

Any area within the 5 gauss line

(Anyone entering needs to have been authorised and undertaken safety checks)

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27
Q

What is an atom made up of?
(3)

A

Protons

Electrons

Neutrons

(PEN)

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28
Q

What charge do protons have?

A

Positive charge

29
Q

What charge do neutrons have?

A

No charge

30
Q

What charge do electrons have?

A

Negative charge

31
Q

How does an atom look like?

A
32
Q

How is motion like in the atom?
(3)

A

Within the nucleus of the atom, the protons and neutrons spin in opposite directions

In atoms with the same number of protons and neutrons, the nucleus itself has no net spin

However if there’s an unequal amount of protons and neutrons, the nucleus itself will have a net spin

33
Q

What is said to be MRI active Nuclei?

A

Atoms with an odd mass number

34
Q

What is the mass number of a hydrogen atom?

A

1

35
Q

What do hydrogen atoms contain?

A

A positively charged proton

36
Q

Hydrogen atoms give a … magnetic moment

A

Large

37
Q

Why are hydrogen atoms used in medical imaging?

A

Because it’s abundant in the human body

38
Q

How does a hydrogen atom look like?

A
39
Q

What happens to the magnetic moments if we don’t have a magnetic field?

A

The magnetic moments are randomly oriented

40
Q

What happens to the magnetic moments when they’re placed in a strong magnetic field?

A

The magnetic moments align (line up) with the magnetic field

41
Q

How can the magnetic moments align with the magnetic field?
(2)

A

Parallel (low energy nuclei)

Anti-parallel (high energy nuclei)

42
Q

What do parallel nuclei create?

A

A net magnetic vector (NMV)

43
Q

How does each hydrogen nucleus spin?

A

It spins on its axis (like a spinning top)

44
Q

What is precession?

A

The spinning of the hydrogen atom’s nucleus

45
Q

What is the precession frequency?

A

The speed that the hydrogen atom’s nucleus spins

46
Q

When does resonance occur?

A

When an object is exposed to an external force that has a frequency close to its own

47
Q

What happens during resonance?
(2)

A

An object is exposed to an external force that has a frequency close to its own

The hydrogen atom’s nucleus gains energy and resonates (quivers)

48
Q

What is excitation?

A

When the radiofrequency pulse that causes resonance to occur is applied

49
Q

What causes resonance to occur?

A

When a radiofrequency pulse is applied

50
Q

What does Bo mean?

A

The magnetic field strength

51
Q

How does the application of a radiofrequency pulse cause resonance to occur?

A

It causes the NMV to move out of alignment with Bo

52
Q

What is the flip angle?

A

The angle between Bo and the NMV

53
Q

What does resonance cause?
(2)

A

The NMV to move out of alignment with Bo

The magnetic moments of the hydrogen nuclei to move in phase with each other

54
Q

Originally all the hydrogen atoms line up what happens when the radiofrequency pulse is added?

A

They move away from each other

55
Q

When is the MRI signal produced?

A

When the in phase magnetism occurs across the receiver coil

56
Q

What happens when the MRI signal is switched off?
(2)

A

The high energy nuclei lose energy

This results in the NMV realigning with Bo (relaxation)

57
Q

What is relaxation?

A

When the NMV realigns with Bo

58
Q

What are the 3 main hazards of MRI?

A

Static magnetic field (Bo)

Time varying magnetic field gradients

Radiofrequency magnetic fields

59
Q

What static magnetic field do scanners used for clinical use have?
(2)

A

1.5T or 3T

60
Q

What are the magnetic field strength hazards?
(3)

A

Sensory effects- dizziness, nausea, metallic taste normally above 2T

Projectile effects- any loose object containing ferromagnetic material will be attracted to the center of the scanner

Torque- metal implants and foreign bodies will try to align with Bo

61
Q

What are the features of the projectile effects?
(3)

A

Any loose object containing ferromagnetic material will be attracted to the center of the scanner

It can reach speeds approaching 45mph entering the bore of the magnet (missile effect)

The attractive force increases as the distance from the isocenter is decreased

62
Q

What is the missile effect?

A

When the speed of the attraction between the ferromagnetic material and the center of the scanner is very high- approaching 45mph

63
Q

What is a quench?
(2)

A

If an incident occurs, the magnetic field strength can be demagnetised.

The liquid helium evaporates

64
Q

How can we cause a quench?

A

Press the quench button

65
Q

What are the consequences of pressing the quench button and causing a quench?
(2)

A

It usually results in irretrievable damage to the MRI machine

The cost of refilling the helium is £8000

66
Q

When should the quench button only be pressed?

A

In exceptional circumstances- if there’s risk to life or limb

67
Q

What happens when a spontaneous quench happens?

A

The helium gas should escape through the quench pipe. If this fails, it escapes into the room

68
Q

What happens if the helium gas escapes into the room after a quench?
(4)

A

The oxygen in the room is forced downwards by the liquid helium

This creates an oxygen deficient to atmosphere

The oxygen is therefore monitored, and an alarm will go off if it fails below 21%

The door should open outwards or there should be a hatch to help with the pressure

Science and Technology 1 (17 decks)

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