The Brain at Work

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The Brain at Work
Dr Sue Francis

• Magnetic Resonance Centre,
• School of Physics and Astronomy
• University of Nottingham

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• Outline of the lecture
• The use of Nuclear Magnetic Resonance (NMR) in
  Brain Imaging

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• Outline of the lecture
• Magnetic Resonance Imaging
• (MRI)

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• Outline of the lecture
• Origin of NMR
• How an NMR image is produced
• MRI Results
• Current MRI Research into Brain Function at
  Nottingham University

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HISTORICAL PERSPECTIVE
1945 NMR discovered 1972 NM imaging invented 1976
First image of human anatomy 1977 First body
image 1983 First commercial scanners
available 1986 First image of a single cell 1992
First Images of brain function
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What is an electromagnetic field?

• All electromagnetic fields travel at the speed of
  light, c 3 x 108 ms-1
• Maxwells Law - EM fields have two components
  ELECTRIC FIELD, E, and MAGNETIC FIELD, B,
  perpendicular to one another.

B
E
C
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Human Body

• Contains water (70)
• Lots of Water Lots of hydrogen nuclei (single
  proton)...

Spinning charged particle (proton)

Similar to current-carrying wire??
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Current-carrying wire
Maxwell's Law
Magnetic field patterns
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Current-carrying wire
N
Bar Magnet
S
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So, Proton Bar Magnet

Known as SPIN
Fundamental to NMR / MRI
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SPIN - Up or down??

• Spins can actually point UP or DOWN in hydrogen

NET MF0

• In the absence of an external magnetic field the
  net magnetization (spin) is 0

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But, in large external magnet field

• Spins can actually point UP or DOWN in hydrogen
• We can change them from up to down state using EM
  energy but only at a specific frequency

NET MF
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Resonant frequency
Absorbed Energy
Spin up to spin down
Resonant frequency depends on external mag field
Frequency of radiowaves
Resonant frequency
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Energy generation
AN RFCOIL This is simply a current loop which
can generate radiowaves. E.g. like a radio
transmitter
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Relaxation

• Spins recover

Measure intensity of RF energy
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Energy measurement
AN RFCOIL Detects radiowaves by inducing a
current. E.g. like a radio antenna
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Imaging

• Person in large Magnetic Field (e.g 1.5 T)
• approximately 30,000 x earths magnetic field!

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Imaging

• Apply RF EM pulse
• Measure received RF energy
• How do we build the image up?
• How do we know where in the body the RF energy
  has come from?
• GRADIENTS...

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Gradients - 1D

• Make magnetic field depend on position in body...

2a
a
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Received RF energy
Resonant frequency depends on external mag field
We know where in the body the two waves came from
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3-D Gradients, x,y,z

• Allow a 3D image to be built up

X
Z
Y
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Contrast in MRI

• Spins recover rate of recovery T1 - depends on
  magnet strength and tissue type

Measure intensity of RF energy
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Contrast in MRI
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Contrast in MRI
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Imaging

• Angiography

• Sports injury

• Abdominal imaging

• Lung imaging

• Fetal imaging

• Brain imaging

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Functional MRI (fMRI)
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Reflex Arc
Pain receptor sensory neuron sends impulses
to the brain motor neuron carries impulse to
finger MOVE!
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Cells in the brain -The Neuron
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Getting the energy
When we perform a task the brain does work the
neurons requires energy - oxygen and
nutrients how do we get these?
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Getting the energy

• Cerebral blood flow increases
• Cerebral blood volume increases
• Cerebral blood oxygenation increases

Lead to Increase in Brightness of MRI signal
- BOLD Effect Blood Oxygenation Level
Dependent effect
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Where does the signal change come from?
Activated State
Baseline
Vessels near to brain cells working to produce
energy
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MRI Signal Change

• BUT this signal change does not occur
  immediately.
• There is a delay in the signal increase of
  approximately 6 sec. - haemodynamic delay.

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Example time course
Image brightness
1 - 2 change
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How do we measure brain activity?

• Take repeated images rapidly during periods of
  rest and stimulation - as signal change is small

• Compare the signal intensities during rest and
  activated states.

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Functional MRI (fMRI)

• Take repeated images during periods of rest and
  stimulation.
• Compare the signal intensities during rest and
  activated states.

• Statistical test (e.g. average)on all points in
  the image.
• Gives activation map.

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Types of stimuli

• Auditory

• Motor

• Visual

• Sensory

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What is the point?

• Recovery from stroke

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Recovery from stroke
lesion
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Recovery from stroke
Motor task in relation to a small lesion
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What is the point?

• Recovery from stroke

• Fetal brain development

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Fetal Brain Development
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Fetal SPM
Auditory study
Eye
Temporal lobe
Central sulcus
Sagittal sinus
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Time course
Auditory study
0985
Signal Intensity
Volume Number
On Off
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What is the point?

• Recovery from stroke

• Fetal brain development

• Blood flow measurements

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Flow maps
veins
arteries
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What is the point?

• Recovery from stroke

• Fetal brain development

• Blood flow measurements

• Used in pre-surgical planning

• How the brain works...

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Acknowledgements

• Andy Gibson
• KK Peck
• Luca Marciani
• Jennie Newton
• Alison Sleigh
• Sarah Gutteridge
• Paul Glover
• Paul Clark

• Penny Gowland
• Richard Bowtell
• Andrew Peters
• Paul Morgan (Academic Radiology)
• Jon Fulford
• Rachel Moore
• Damien Tyler
• Ron Coxon