Title: Magnetic Resonance Imaging
1Magnetic Resonance Imaging
2Magnetic field gradients
3Gradient echo
4Gradient echo
5Maxwell Pair
a
3
dB
Maxwell Pair for
z
dz
Net B field from coils
a
Local fields
Current paths
B
o
6Straight wires
dB
Straight wires for
z
dy
Reduces B
o
Increases B
o
y
B
o
z
7Gradient 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
8Gradients can be combined to produce gradients in
arbitrary directions
9Slice selection using gradients
Sample
Bz
B(x1)
B(x2)
x
x1
x2
10Slice selection
11Imaging in gradients
Sample
Bz
B(x1)
B(x2)
x
x1
x2
Signal (spectrum)
Frequency
w1
w2
PROJECTION
12(No Transcript)
13Projection Reconstruction
14Projection Reconstruction
15Basic reconstruction
X-ray beam is attenuated forming a projection
16Projections are collected from various directions
17The projection tells you that the beam was
attenuated with equal probability anywhere along
its path
18(No Transcript)
19(No Transcript)
20Projection Reconstruction
- Diffusion imaging
- Radial Spin Echo and TSE Scan PR
- Low sensitivity to motion
- Low sensitivity to susceptibility artifacts
21Projection Reconstruction
- Sodium Imaging
- Human Skeletal Muscle Sodium MR Imaging and
Quantification-Potential Applications in Exercise
and Disease - Constantinides, Gillen, Boada, Pomper, Bottomley,
- Radiology
22K-space
Image
23K space
Units rad/ m
Increasing spatial frequency
24Projection Reconstruction
25With MRI we can control how we sample k-space
26Phase encoding
Phase encoding
Readout gradient
Initial phase during readout depends on phase
encoding amplitude
27Phase encoding
Phase encoding
Readout gradient
Initial phase during readout depends on phase
encoding amplitude
28With MRI we can control how we sample k-space
29Spin warp imaging
Wicklow, Washington University, St. Louis
30Roger Ordidge, UCL
31Ultrashort TE- Tendons
32(No Transcript)
33Motion artefacts
Anesthetic
Steve Keevil UMDS
34EPI
35Diffusion EPI
36Diffusion
37EPI- fetus
38EPI- gut
39EPI - fMRI
Cochlear Stimulation
Ludman, Mason, ODonoghue, Morris, Nottingham