Transcript The importance of MRI, a few numbers

The importance of MRI, a few
numbers

10 000 MRI units worldwide in 2003

75 millions scans per year performed

Constant need for over 1000 MRI technologists per year

MRI magnet have 1.5-2.0 Tesla (same strength as
magnet used in car junk yard)
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1 Tesla=10 000 gauss, earth magnetic field=0.5 gauss
Background Info on Magnetic
Resonance
 Proton
imaging and the use of hydrogen
 Magnetic
field of H
 Behaviour
 Nuclear
in an external magnetic field
magnetic resonance
How is an image obtained?

Isolation of slice of tissue
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Creation of a magnetic field
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The perpendicular magnetic field
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Repetition at different angles
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Collection of data in computer and Fourier
transform
Tissue
CSF
T1 (s)
0.8 - 20
0.76 White
1.08
1.09 Gray
2.15
Meninges 0.5 - 2.2
0.95 Muscle
1.82
Adipose 0.2 - 0.75
T2 (ms)
110 2000
61-100
61 - 109
50 - 165
20 - 67
53 - 94
Diagram taken from “Basics of Magnetic Resonance Imaging” p.21
What can we deduce from the H
values obtained?
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The behaviour of regional hydrogen
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T1 of hydrogen
Time required for the hydrogen nuclei to emit 63% of absorbed energy
from stimulating pulse
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T2 of hydrogen (relaxation constant)
Time necessary for 63% of signal to be lost due to dephasing

Factors affecting T1 and T2
Main component of an MRI
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Main magnetic field
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The problem of electrical
resistance
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Aluminium as the
conductor of choice

Gradient coils
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Rf coils (radio frequency
source and pulse
programmer)
MRI Limitations

Shape and size
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Scanning time
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Gradient coil and noise
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Patient discomfort

Pacemaker and artificial body part
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Complexity and cost
Advantages of MRI
 Bones
 Any
are invisibles
plane can be scanned
 Tissue
 Less
characterization
tissue heating
The Future of MRI
 The
trend toward lower field strength
 Understanding Alzheimer’s
 Non-invasive
 Open
disease
quantification of blood flow
doors in understanding brain
processes