MRI

Question 1

MRI

Answer 1

Magnetic resonance imaging

Question 2

Basic magnetism

Answer 2

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

Question 3

What is the strength of a magnetic field measured in

Answer 3

Teslas

Question 4

Magnetic moment

Answer 4

Quantity that represents the direction and strength of a magnetic field

The stronger the magnetic field the stronger the magnetic moment

Question 5

MRI magnet

Answer 5

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

Question 6

Superconducting magnet

Answer 6

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

Question 7

Radio frequency coils

Answer 7

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

Produced via radio frequency transmitter coils

Coils located iwthin the magnet

Question 8

Receiver coils

Answer 8

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

Question 9

Controlled area

Answer 9

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

Question 10

MRI environment

Answer 10

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

Question 11

An atom is made up of

Answer 11

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

Question 12

Motion in the atom

Answer 12

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

Question 13

If there is an unequal amount of protons and neutrons …

Answer 13

The nucleus itself will have a net spin

Question 14

MRI active nuclei

Answer 14

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

Question 15

Hydrogen atoms

Answer 15

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

Question 16

Alignment of magnetic field and moments

Answer 16

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

Question 17

Procession

Answer 17

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

Question 18

Resonance

Answer 18

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

Question 19

Phase

Answer 19

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

Question 20

MRI signal

Answer 20

Produced when the in phase magnetism occurs across the receiver coil

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

Question 21

Relaxation

Answer 21

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

Question 22

3 main hazards of MRI

Answer 22

Static magnetic field

Time varying magnetic gradients

Radio frequency magnetic fields

Question 23

Static magnetic field

Answer 23

Always present

Question 24

3 Magnetic field strength hazards

Answer 24

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

Question 25

Quench

Answer 25

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

Question 26

Spontaneous quench

Answer 26

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

Question 27

Spontaneous quench and helium escaping into the room leads to

Answer 27

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