MRI Flashcards

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1
Q

MRI

A

Magnetic resonance imaging

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2
Q

Basic magnetism

A

A magnetic field is a region of space in which magnetic forces are experienced

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3
Q

What is the strength of a magnetic field measured in

A

Teslas

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4
Q

Magnetic moment

A

Quantity that represents the direction and strength of a magnetic field

The stronger the magnetic field the stronger the magnetic moment

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5
Q

MRI magnet

A

Requires a very strong magnetic field
Achieved by superconducting an electromagnet.
Electromagnet is configured using wire in the shape of a coil

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6
Q

Superconducting magnet

A

Electromagnet made from coils of superconducting wire
High resistance increases the temperature of the coil
Needs to be cooled to a low temperature for it to operate
MRI scanner is cooled with liquid helium

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7
Q

Radio frequency coils

A

to produce an image a radio frequency pulse is administered to the patient

Produced via radio frequency transmitter coils

Coils located iwthin the magnet

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8
Q

Receiver coils

A

Surface coils

Receive the MRI signal
Designed especially for certain areas
Need to be placed over the area to be imaged and as close to the patient as possible

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9
Q

Controlled area

A

Control room
Scanning room
MEI equipment room
Access to theses areas are restricted

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10
Q

MRI environment

A

Area within the gauss line
Any one entering needs to have been authorised and undertaken safety checks

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11
Q

An atom is made up of

A

Protons ( positive charge)
Neutrons ( no charge)
Electrons (negative charge )

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12
Q

Motion in the atom

A

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

In atom with the same no of protons and neutrons the nucleus itself has no net spin

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13
Q

If there is an unequal amount of protons and neutrons …

A

The nucleus itself will have a net spin

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14
Q

MRI active nuclei

A

Atoms with an odd mass number are said to be MRI active nuclei
Have a tendency to align their axis of rotation to an applied magnetic field

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15
Q

Hydrogen atoms

A

Have a mass number of 1
Positively charged proton
Gives a large magnetic moment
Used in medical imaging as its abundant in the human body

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16
Q

Alignment of magnetic field and moments

A

Without a magnetic field the magnetic moments are randomly orientated

When placed in a a strong magnetic field the magnetic moments align. With this field

Some align parallel and anti-a parallel

The parallel nuclei crates a net magnetic vector

17
Q

Procession

A

each hydrogen nucleus is spinning on its axis
The magnetic field strength causes an addition spin -procession
Speed at which they spin is called the procession frequency

18
Q

Resonance

A

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

The nucleus gains energy and resonates

Application of the radio frequency pulse that causes resonance to occur is called excitation

19
Q

Phase

A

Another result of resonance is the magnetic moments of the hydrogen nuclei that move in phase with each other

20
Q

MRI signal

A

Produced when the in phase magnetism occurs across the receiver coil

Due to the moving transverse magnetization producing magnetic fields fluctuations inside the coil

21
Q

Relaxation

A

when the signal is switched off the Hugh energy nuclei loses its energy

22
Q

3 main hazards of MRI

A

Static magnetic field

Time varying magnetic gradients

Radio frequency magnetic fields

23
Q

Static magnetic field

A

Always present

24
Q

3 Magnetic field strength hazards

A

Sensory effects- dizziness nausea metallic taste

Projectile effects p loose objects will be attracted to the Center of the scanner

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

25
Q

Quench

A

If an incident occurs the magnetic fields strength can be demagnetised
Liquid helium evaporates
Known as quench
Activiated by pressing the quench button
Only pressed if there is a risk to life or limb
Results in damage to the MRI system
Cost of refilling helium is £8k

26
Q

Spontaneous quench

A

Helium gas escaped through quench pipe
However if this fails it espcapes into the room

27
Q

Spontaneous quench and helium escaping into the room leads to

A

Oxygen deficient atmosphere

Oxygen in room decreases by the liquid helium in the room

Oxygen is then monitored and if it falls below 21% and alarm goes off