MRI Images

1
MRI Images Magnetic Resonance Imaging
MRI scan of the brain
2
What Is MRI?
MRI stands for Magnetic Resonance Imaging It is
used in the medical industry It is an advanced
alternative to x-ray
3
Slices taken about every second, about 1mm
apart 2D images are compiled together to create
a 3D image which can be studied from many
different angles on the computer Show soft
tissue rather than bone structure shown by
X-Ray Can diagnose tumours, infections,
strokes and visualise injuries
4
fMRI Images
fMRI vs MRI
MRI shows the structure of organs and
tissue fMRI shows organ activity
5
Using fMRI Images
The brain can be scanned to find different areas
activated with specific tasks
Love
Joy
6
Fear
Smell
Pain
7
How Does It All Work?
Lets take a look further into Magnetic Resonance
Imaging.. First the Magnetism!
8
What Does Magnetism Have To Do With The Body?
Lets look at what we know.
How does the body react to increased activity
(exercise)?
Increased activity in area of brain - increased
volume of blood - increased speed of blood -
increased amount of oxygen in blood
What does oxygen have to do with magnetism?
Oxygen is carried around the body in
haemoglobin. Haemoglobin is diamagnetic when
its oxygenated.
9
So What Is Diamagnetism?
Do you remember how (ferro)magnetism
works? Making a needle magnetised..
10
So Onto To Diamagnetism
Its a repulsive form of magnetism.. The
magnetic field works in the opposite direction to
domain
Frog!
So what does this mean we can do?
11
What Does This Have To Do With MRI?
MRI scanners work on a basis of diamagnetism A
different level of oxygenation gives a different
signal. This will be looked into further when we
start to understand resonance
12
BOLD. What???
The signal is detected depending on oxygenation
of blood This is known as Blood Oxygen Level
Dependant Contrast
Active brain quick blood flow through tissue
raised oxygen levels
More brain activity more oxygen more intense
signal
13
How Is The Signal Produced?
If you exercise, what happens to the oxygen?
It gets used up.. This happens in the brain as
well This makes the haemoglobin
deoxygenated Deoxygenated haemoglobin is
paramagnetic Switching forms of magnetism
changes magnetic resonance
14
So What Is Paramagnetism?
Paramagnetism is a temporary form of
magnetism. The material becomes magnetic when in
another magnetic field. When this field stops,
they cease to be magnetic.
15
So weve been going on about Resonance . What is
it???
Every material will vibrate at a particular
natural frequency If you vibrate the material
at the right frequency, it will go
crazy!!!..... RESONATE
16
Lets Try It Out!!
17
MRI simulation
18
So What Is The Link?
An organ is like any other material, with a
natural frequency Radio waves are directed at
specific areas At the right frequency, the
protons in the organ will resonate
19
So What Is A Photon?

• A photon carries electromagnetic radiation
• Radio Waves
• Microwaves
• Infra Red
• Visible Light
• Ultra Violet
• X-Rays
• Gamma

20
How Do Diamagmetism and Magnets Link?
Materials contain atoms with orbiting
electrons. Electrons are affected by
external magnetic fields.
21
How Are The Electrons Affected?
They will change their orbits due to the external
magnetic field. This change creates
a repelling magnetic field.
Clockwise orbit
Anticlockwise orbit
22
The Scanner
23
The Magnets

• Due to the power of the magnets youre allowed no
  metallic objects or pacemakers.
• Pallet Jacks
• Oxygen Tanks
• Office chairs
• Pens
• Have become stuck in MRI scanners.

24
The Magnets

• Primary Magnet
• A coil of wire with an electrical current running
  through it.
• To generate a strong enough magnetic field, the
  wire must be bathed in liquid Helium, cooling it
  to -269c.
• This gets rid of any resistance in the wires and
  creates a magnetic field strength 20000 times
  that of the earth.

25
The Magnets

• Gradient Magnet
• Three smaller magnets 1/1000 times less magnetic
  than the primary magnet allow the magnetic field
  to be altered slightly.
• They allow very precise cross sections to be
  taken of targeted areas that are of interest to
  the operator.

26

• Radio Frequency Coil
• Emits and detects photons
• Show areas with a greater blood flow
• areas of high activity emit radio photons of a
  particular frequency.

27
How the image is produced

• Scanners are in a room shielded by a faraday
  cage similar to that on the window of microwave
  ovens.

• The object, or person is placed within the
  scanner.
• Gradient magnets used to target a specific
  slice of the object.
• Radio waves are emitted and detected by the RF
  coil.

28
Basics Of Imaging
1 byte 8 bits 256 colours/alternatives (0-255)
28 8 bits (1 byte) Used for greyscale colour
29
How the image is produced

• The intensity is digitised and given a number on
  a scale of 0-255.
• The values of these intensities are converted to
  show increasing shades of grey.

• The greater the brain activity the darker the
  area of the picture.
• False colour is often added to clearly show the
  areas of the brain using more oxygen at specific
  points in time.

30
How Much HaveYou Learnt??