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Magnetic Resonance Imaging

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Magnetic Resonance Imaging EPI Diffusion EPI Diffusion EPI- fetus Fetal Brain Placenta Fetal Lung Fetal Liver EPI- gut EPI - fMRI Ludman, Mason, O Donoghue, Morris ... – PowerPoint PPT presentation

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Title: Magnetic Resonance Imaging


1
Magnetic Resonance Imaging
2
Magnetic field gradients
3
Gradient echo
4
Gradient echo
5
Maxwell Pair
a
3
dB
Maxwell Pair for
z
dz
Net B field from coils
a
Local fields
Current paths
B
o
6
Straight wires
dB
Straight wires for
z
dy
Reduces B
o
Increases B
o
y
B
o
z
7
Gradient field Acoustic noise
  • One of the biggest challenges at high field
  • Acoustic noise
  • Ear defenders and foam to reduce bone conduction
  • Gradient system decoupled from bed (and room)
  • Modification of gradient waveforms
  • Novel gradient coil designs

Conventional Waveform
Minimum slew rate waveforms
8
Gradients can be combined to produce gradients in
arbitrary directions
9
Slice selection using gradients
Sample
Bz
B(x1)
B(x2)
x
x1
x2
10
Slice selection
11
Imaging in gradients
Sample
Bz
B(x1)
B(x2)
x
x1
x2
Signal (spectrum)
Frequency
w1
w2
PROJECTION
12
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13
Projection Reconstruction
14
Projection Reconstruction
15
Basic reconstruction
X-ray beam is attenuated forming a projection
16
Projections are collected from various directions
17
The projection tells you that the beam was
attenuated with equal probability anywhere along
its path
18
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19
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20
Projection Reconstruction
  • Diffusion imaging
  • Radial Spin Echo and TSE Scan PR
  • Low sensitivity to motion
  • Low sensitivity to susceptibility artifacts

21
Projection Reconstruction
  • Sodium Imaging
  • Human Skeletal Muscle Sodium MR Imaging and
    Quantification-Potential Applications in Exercise
    and Disease
  • Constantinides, Gillen, Boada, Pomper, Bottomley,
  • Radiology

22
K-space
Image
23
K space
Units rad/ m
Increasing spatial frequency
24
Projection Reconstruction
25
With MRI we can control how we sample k-space
26
Phase encoding
Phase encoding
Readout gradient
Initial phase during readout depends on phase
encoding amplitude
27
Phase encoding
Phase encoding
Readout gradient
Initial phase during readout depends on phase
encoding amplitude
28
With MRI we can control how we sample k-space
29
Spin warp imaging
Wicklow, Washington University, St. Louis
30
Roger Ordidge, UCL
31
Ultrashort TE- Tendons
32
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33
Motion artefacts
Anesthetic
Steve Keevil UMDS
34
EPI
35
Diffusion EPI
36
Diffusion
37
EPI- fetus
38
EPI- gut
39
EPI - fMRI
Cochlear Stimulation
Ludman, Mason, ODonoghue, Morris, Nottingham
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