Part III Physics: Medical
Physics Magnetic
Resonance Imaging
2006
Part III Physics:
Medical Physics Option
Magnetic Resona...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Lecture Content
Lecture I
– Overview of Nuclear Magnet...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Lecture Content
Lecture II
– How does NMR become MRI
–...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Useful Web Sites
Rochester Institute:
http://www.cis.r...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
PD- T2 weighted with full
coverage
TR 6055, TEeff 20
&...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
PD- T2 weighted -
Pituitary Tumour
TR 6055, TEeff 20
&...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
PD- T2 weighted -
Glioma
TR 6055, TEeff 20
& 120, ETL ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
NMR History
1921: Compton: electron spin
1924: Pauli: ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
NMR History
1976: Lauterbur: First NMR
image of sample...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Nuclear Zeeman Effect
Application of strong magnetic f...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Population Difference
Given by Boltzman Statistics:
nα...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Semi-Classical Model
Gyroscopic motion of magnetic mom...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Ensemble Average
M
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Rotating Frame
Consider precessing moment in a frame o...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Rotating Frame
Classical treatment of M
Effect of RF i...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Rotating Frame
Classical treatment of M
Effect of RF i...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Rotating Frame
Classical treatment of M
Effect of RF i...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Rotating Frame
Classical treatment of M
Effect of RF i...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Rotating Frame
Classical treatment of M
Effect of RF i...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Rotating Frame
Classical treatment of M
Effect of RF i...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Rotating Frame
Classical treatment of M
Effect of RF i...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Rotating Frame
Classical treatment of M
Effect of RF i...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Signal Detection
rotating Frame:
Y’X’
B0
YX
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Fourier Transformation
FT
Sampling frequency = 2 expec...
Basic Spin Echo Imaging 28
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Effect of RF pulses:
B1 (rf...
Basic Spin Echo Imaging 29
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Effect of RF pulses:
B1 (rf...
Basic Spin Echo Imaging 30
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Effect of RF pulses:
B1 (rf...
Basic Spin Echo Imaging 31
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Effect of RF pulses:
B1 (rf...
Basic Spin Echo Imaging 32
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Effect of 180o
RF pulses:
B...
Basic Spin Echo Imaging 33
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Effect of 180o
RF pulses:
B...
Basic Spin Echo Imaging 34
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Effect of 180o
RF pulses:
B...
Basic Spin Echo Imaging 35
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Effect of 180o
RF pulses:
B...
Basic Spin Echo Imaging 36
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Effect of 180o
RF pulses:
B...
Basic Spin Echo Imaging 37
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Effect of 180o
RF pulses:
B...
Basic Spin Echo Imaging 38
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Effect of 180o
RF pulses:
B...
Basic Spin Echo Imaging 39
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Effect of 180o
RF pulses:
B...
Basic Spin Echo Imaging 40
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Effect of 180o
RF pulses:
B...
Basic Spin Echo Imaging 41
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Effect of 180o
RF pulses:
B...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Two Pulse sequences (I)
90——τ ——90
Saturation recovery...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
T1 Spin Lattice
Relaxation Time
Describes the return t...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Two Pulse sequences (II)
90——τ ——180 ——τ ——
Spin Echo ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Two Pulse sequences (II)
90——τ ——180 ——τ ——
Spin Echo ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Two Pulse sequences (II)
90——τ ——180 ——τ ——
Spin Echo ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Two Pulse sequences (II)
90——τ ——180 ——τ ——
Spin Echo ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Two Pulse sequences (II)
90——τ ——180 ——τ ——
Spin Echo ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Two Pulse sequences (II)
90——τ ——180 ——τ ——
Spin Echo ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Two Pulse sequences (II)
90——τ ——180 ——τ ——
Spin Echo ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Two Pulse sequences (II)
90——τ ——180 ——τ ——
Spin Echo ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Two Pulse sequences (II)
90——τ ——180 ——τ ——
Spin Echo ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Two Pulse sequences (II)
90——τ ——180 ——τ ——
Spin Echo ...
Basic Spin Echo Imaging 54
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
T2 and T2
*
e
-t/
T2
*
e
-t...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Spin-Spin Relaxation
Time
Static inhomogeneities refoc...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Bloch Equations
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Superconducting Magnet
Helium vessel
containing super-...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Superconducting Magnet
Bore B0
100cm 0 4T
80cm 0 8T
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Shimming
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Other Magnet Types
Permanent magnet, e.g.
light weight...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Other Magnet Types
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Other Magnet Types
Electromagnet <0.3T
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Special Superconducting
Magnets
Active Shielding
– Ext...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
RF Coils
Remember Brf must be  B0
Field is  subject,...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
RF Coils
Remember Brf must be  B0
Field is  subject,...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Lecture Content
Lecture II
– How does NMR become MRI
–...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
How to Make Images
Impose (separately):
δBz
δx
δBz
δy
...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
How to make images
For a Z gradient
-hz +hz
ωz = -γ(B0...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
How to make images
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Imaging Gradients
Special coils (together with power
s...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Imaging Gradients
Special coils (together with power
s...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Selection of Slice
Use Fourier relationship:
RF Amplit...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Selection of slice
Slice thickness
adjusted by
changin...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
k-space
k-space is the raw data space
before fourier t...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Image vs k-space
ρ(r) S(k
)k(t)=
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Image vs k-space
ρ(r) S(k
)
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Image vs k-space
ρ(r) S(k
)
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Image vs k-space
ρ(r) S(k
)
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Image vs k-space
ρ(r) S(k
)
FT
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Information in k-space
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
GE k-space trajectory
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
GE k-space traj...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
GE k-space traj...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE k-sp...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE k-sp...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE k-sp...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE k-sp...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE k-sp...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE k-sp...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE k-sp...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE k-sp...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE k-sp...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE k-sp...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE k-sp...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE k-sp...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE k-sp...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE k-sp...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE k-sp...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE k-sp...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
-kr +kr
-kp
+kp
SE k-space trajectory
RF
GS...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
-kr +kr
-kp
+kp
SE k-space trajectory
RF
GS...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
-kr +kr
-kp
+kp
SE k-space trajectory
RF
GS...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
-kr +kr
-kp
+kp
SE k-space trajectory
RF
GS...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
-kr +kr
-kp
+kp
SE k-space trajectory
RF
GS...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
-kr +kr
-kp
+kp
SE k-space trajectory
RF
GS...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Definitions
RF
GS
GR
GP
S(t)
TR
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Definitions
RF
GS
GR
GP
S(t)
TE
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
1 2 3 4 5 6
T1
1 2 3 4 5 6
T2
Controlling contrast
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
1 2 3 4 5 6
T1
1 2 3 4 5 6
T2
Proton Density
TR TE
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
1 2 3 4 5 6
T1
1 2 3 4 5 6
T2
T2 Contrast
TR TE
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
PD- T2 weighted with full
coverage
TR 6055, TEeff 20
&...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
1 2 3 4 5 6
T1
1 2 3 4 5 6
T2
T1 Contrast
TR TE
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Alzheimer’s
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
1 2 3 4 5 6
T1
1 2 3 4 5 6
T2
*
T2
*
Contrast
TR TE
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
T2 and T2* of acute head
injury
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Effect of Flip angle α
X’ Y’
B0
Brf
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Effect of Flip angle α
X’ Y’
B0
Brf
90o
pulse
Maximum
...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Effect of Flip angle α
X’ Y’
B0
Brf
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Effect of Flip angle α
X’ Y’
B0
Brf
Flip angle 30o:
de...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
TR/TE/
α
41/9/15
500/9/15
41/9/9041/9/60
500/9/90
Cont...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Why does MRI take so
long
Answer
– Only one phase enco...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Pulse sequence
RF
G1
Gslice
G2
Rx
Multiple spin echos
...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
RARE k-space trajectory
-kr +kr
-kp
+kp
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
RARE k-space trajectory
-kr +kr
-kp
+kp
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
RARE k-space trajectory
-kr +kr
-kp
+kp
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
RARE k-space trajectory
-kr +kr
-kp
+kp
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
RARE k-space trajectory
-kr +kr
-kp
+kp
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
RARE k-space trajectory
-kr +kr
-kp
+kp
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
RARE k-space trajectory
-kr +kr
-kp
+kp
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Echo Planar Imaging
Fastest imaging method
Typical AQ ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Why ?
freeze involuntary patient motion
visualization ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE-PEI ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE EPI ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE EPI ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE EPI ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE EPI ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE EPI ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE EPI ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE EPI ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
ρ(r) S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE EPI ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE EPI k-spa...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
S(k
)
RF
G S
G R
G P
S(t)
-kr +kr
-kp
+kp
GE EPI k-spa...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
GE vs EP Imaging
TE
ms
TR
ms
AQ
ms
BW
khz
Gread
mT/m
S...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
GE vs EP Imaging
TE
ms
TR
ms
AQ
ms
BW
khz
Gread
mT/m
S...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
MRI at
3T
128x128 single shot,
GE echo planar.
X,Y,Z s...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
fMRI (functional MRI)
Monitor T2 or T2* contrast durin...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Echo-Planar fMRI
response stimulus
GE-images with EPI
...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
oxyhaemoglobin
deoxyhaemoglobin
Resting
O2 & glucose
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
O2 & glucose
Blood flow
‘over-compensation’
%O2
Activa...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Effect of Intravascular
Oxygenation level
Blood vessel...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
T2* curves activated and
rest
time (ms)
signal
activat...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Unilateral Finger
Opposition (high res)
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Definitions
Diffusion relates to the
microscopic Brown...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Effect of Diffusion on
NMR
Rms. of an ensemble is zero...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Diffusion and Spin echoes
δ δ
∆
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Diffusion and Spin echoes
I/I0 = e -bD
b = γ2
g2
δ2
(∆...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
D and ADC
0
2
4
6
8
10
0 500 1000 1500
water
DMSO
I/I0...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Diffusion Weighted
Imaging
RF
G
sG
rGp
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Diffusion Weighted
Imaging
RF
G
sG
rGp
Gdiffusion
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
δ δ
∆
0
2
4
6
8
10
0 500 1000 1500
water
DMSO
Typical ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Practical Problems in Human
DWI
Gross Motion
– Head mo...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Practical Problems in Human
DWI
Gross Motion
– Echo Pl...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Diffusion Weighted EPI (b=1570 s/mm2
)
READ PHASE SLIC...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Cambridge NIH van Zijl
ADCtrace
Diffusion Weighted EPI...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Diffusion Weighted EPI (b=1570 s/mm2
)AnistropyIndex
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
MRI and O15
water PET
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Gadolinium blous experiment in rat brain
Imagenumber(r...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Effect of Intravascular Gd
Blood vessel
Tissue
Tissue
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Effect of Intravascular Gd
Blood vessel
Tissue
Tissue
...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Gadolinium blous experiment in rat brain
Imagenumber(r...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Data Analysis
Fit first pass of the bolus (avoid
recir...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Perfusion weighted MRI of a patient with a high
grade ...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
Caution
Numbers obtained are not for true
perfusion (a...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
True Perfusion by MRI
Arterial spin labeling
– EPISTAR...
Part III Physics: Medical Physics
Option Magnetic Resonance
Imaging
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Part III Physics: Medical Physics Magnetic Resonance Imaging

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Part III Physics: Medical Physics Magnetic Resonance Imaging

  1. 1. Part III Physics: Medical Physics Magnetic Resonance Imaging 2006 Part III Physics: Medical Physics Option Magnetic Resonance Imaging Dr T A Carpenter http://www.wbic.cam.ac.uk/~tac12
  2. 2. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Lecture Content Lecture I – Overview of Nuclear Magnetic Resonance – Excitation and Signal detection – One pulse and Two pulse experiments – Hardware
  3. 3. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Lecture Content Lecture II – How does NMR become MRI – Effects of Magnetic Field Gradients – Imaging pulse sequences – contrast – examples
  4. 4. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Useful Web Sites Rochester Institute: http://www.cis.rit.edu/htbooks/mri/mri-main.htm
  5. 5. Part III Physics: Medical Physics Option Magnetic Resonance Imaging
  6. 6. Part III Physics: Medical Physics Option Magnetic Resonance Imaging PD- T2 weighted with full coverage TR 6055, TEeff 20 & 120, ETL = 10, 512x240, 35.84 x 16.8. 27 5mm slices. Scan time 5mins >360 acquired this year Work horse scan for screening Could contrast, better deep grey matter than FSE at 1.5T
  7. 7. Part III Physics: Medical Physics Option Magnetic Resonance Imaging PD- T2 weighted - Pituitary Tumour TR 6055, TEeff 20 & 120, ETL = 10, 512x240, 35.84 x 16.8. 27 5mm slices. Scan time 5mins
  8. 8. Part III Physics: Medical Physics Option Magnetic Resonance Imaging PD- T2 weighted - Glioma TR 6055, TEeff 20 & 120, ETL = 10, 512x240, 35.84 x 16.8. 27 5mm slices. Scan time 5mins
  9. 9. Part III Physics: Medical Physics Option Magnetic Resonance Imaging
  10. 10. Part III Physics: Medical Physics Option Magnetic Resonance Imaging
  11. 11. Part III Physics: Medical Physics Option Magnetic Resonance Imaging NMR History 1921: Compton: electron spin 1924: Pauli: Proposes nuclear spin 1946: Stanford/Harvard group detect first NMR signal mid -50 to mid 70’s NMR become powerful tool for structural analysis mid-70 first superconducting
  12. 12. Part III Physics: Medical Physics Option Magnetic Resonance Imaging NMR History 1976: Lauterbur: First NMR image of sample tubes in a chemical spectrometer 1981: First commercial scanners <0.2T 1985: 1.5T scanner 1986: Rapid developments in SNR, resolution etc 1998: Whole body 8T at OSU
  13. 13. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Nuclear Zeeman Effect Application of strong magnetic field B0 lifts degeneracy of nuclear spin levels For spin 1/2: ∆E = γ h B0 γ Gyromagnetic ratio (constant of nucleus) For hydrogen γ = 42.5 Mhz/T ∆E
  14. 14. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Population Difference Given by Boltzman Statistics: nα = exp( -γhBo /kT ) nβ population difference is small <1 in 106 NMR is very insensitive
  15. 15. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Semi-Classical Model Gyroscopic motion of magnetic moment about B0 B0 Use classical mechanics(Larmor) w0 = - γ B0 µ
  16. 16. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Ensemble Average M
  17. 17. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Rotating Frame Consider precessing moment in a frame of reference rotating at the larmor frequency around B0 x y ω = γBo X’ Y’
  18. 18. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Rotating Frame Classical treatment of M Effect of RF in laboratory Frame:Y X Equivalent to sinusoidal Brf
  19. 19. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Rotating Frame Classical treatment of M Effect of RF in rotating Frame: Y X X’ Y’ B0 Brf
  20. 20. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Rotating Frame Classical treatment of M Effect of RF in rotating Frame: Y X X’ Y’ B0 Brf
  21. 21. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Rotating Frame Classical treatment of M Effect of RF in rotating Frame: Y X X’ Y’ B0 Brf
  22. 22. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Rotating Frame Classical treatment of M Effect of RF in rotating Frame: Y X X’ Y’ B0 Brf
  23. 23. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Rotating Frame Classical treatment of M Effect of RF in rotating Frame: Y X X’ Y’ B0 Brf
  24. 24. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Rotating Frame Classical treatment of M Effect of RF in rotating Frame: Y X X’ Y’ B0 Brf
  25. 25. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Rotating Frame Classical treatment of M Effect of RF in rotating Frame: Y X X’ Y’ B0 Brf
  26. 26. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Signal Detection rotating Frame: Y’X’ B0 YX
  27. 27. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Fourier Transformation FT Sampling frequency = 2 expected frequency spread (Nyquist)
  28. 28. Basic Spin Echo Imaging 28 Part III Physics: Medical Physics Option Magnetic Resonance Imaging Effect of RF pulses: B1 (rf) y’ y’ x’ x’ z zB0 90o degree pulse
  29. 29. Basic Spin Echo Imaging 29 Part III Physics: Medical Physics Option Magnetic Resonance Imaging Effect of RF pulses: B1 (rf) y’ y’ x’ x’ z zB0 90o degre e pulse
  30. 30. Basic Spin Echo Imaging 30 Part III Physics: Medical Physics Option Magnetic Resonance Imaging Effect of RF pulses: B1 (rf) y’ y’ x’ x’ z zB0 180o pulse (invertin g pulse)
  31. 31. Basic Spin Echo Imaging 31 Part III Physics: Medical Physics Option Magnetic Resonance Imaging Effect of RF pulses: B1 (rf) y’ y’ x’ x’ z zB0 180o pulse (invertin g pulse)
  32. 32. Basic Spin Echo Imaging 32 Part III Physics: Medical Physics Option Magnetic Resonance Imaging Effect of 180o RF pulses: B1 (rf) y’ y’ x’ x’ z zB0 180o degre e pulse
  33. 33. Basic Spin Echo Imaging 33 Part III Physics: Medical Physics Option Magnetic Resonance Imaging Effect of 180o RF pulses: B1 (rf) y’ y’ x’ x’ z zB0 180o degre e pulse
  34. 34. Basic Spin Echo Imaging 34 Part III Physics: Medical Physics Option Magnetic Resonance Imaging Effect of 180o RF pulses: B1 (rf) y’ y’ x’ x’ z zB0 180o degre e pulse
  35. 35. Basic Spin Echo Imaging 35 Part III Physics: Medical Physics Option Magnetic Resonance Imaging Effect of 180o RF pulses: B1 (rf) y’ y’ x’ x’ z zB0 180o degre e pulse
  36. 36. Basic Spin Echo Imaging 36 Part III Physics: Medical Physics Option Magnetic Resonance Imaging Effect of 180o RF pulses: B1 (rf) y’ y’ x’ x’
  37. 37. Basic Spin Echo Imaging 37 Part III Physics: Medical Physics Option Magnetic Resonance Imaging Effect of 180o RF pulses: B1 (rf) y’ y’ x’ x’
  38. 38. Basic Spin Echo Imaging 38 Part III Physics: Medical Physics Option Magnetic Resonance Imaging Effect of 180o RF pulses: B1 (rf) y’ y’ x’ x’
  39. 39. Basic Spin Echo Imaging 39 Part III Physics: Medical Physics Option Magnetic Resonance Imaging Effect of 180o RF pulses: B1 (rf) y’ y’ x’ x’
  40. 40. Basic Spin Echo Imaging 40 Part III Physics: Medical Physics Option Magnetic Resonance Imaging Effect of 180o RF pulses: B1 (rf) y’ x’ y’ x’ y’ x’ y’ x’
  41. 41. Basic Spin Echo Imaging 41 Part III Physics: Medical Physics Option Magnetic Resonance Imaging Effect of 180o RF pulses: B1 (rf) y’ x’ y’ x’ y’ x’ y’ x’
  42. 42. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Two Pulse sequences (I) 90——τ ——90 Saturation recovery Two Pulse sequences (I) 180——τ ——90 Inversion recovery 1 2 3 4 5 6 T1 1 2 3 4 5 6 T1
  43. 43. Part III Physics: Medical Physics Option Magnetic Resonance Imaging T1 Spin Lattice Relaxation Time Describes the return to equilibrium for spins from the excited state Spins loose heat to the rest of the world Requires fluctuating magnetic field near the Larmor frequency for an effective transfer of energy from a spin to surrounding lattice
  44. 44. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Two Pulse sequences (II) 90——τ ——180 ——τ —— Spin Echo sequence y’ x’
  45. 45. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Two Pulse sequences (II) 90——τ ——180 ——τ —— Spin Echo sequence y’ x’
  46. 46. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Two Pulse sequences (II) 90——τ ——180 ——τ —— Spin Echo sequence y’ x’
  47. 47. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Two Pulse sequences (II) 90——τ ——180 ——τ —— Spin Echo sequence y’ x’
  48. 48. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Two Pulse sequences (II) 90——τ ——180 ——τ —— Spin Echo sequence y’ x’ e -t/ T2 * e -t/ T2
  49. 49. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Two Pulse sequences (II) 90——τ ——180 ——τ —— Spin Echo sequence y’ x’ e -t/ T2 * e -t/ T2
  50. 50. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Two Pulse sequences (II) 90——τ ——180 ——τ —— Spin Echo sequence y’ x’
  51. 51. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Two Pulse sequences (II) 90——τ ——180 ——τ —— Spin Echo sequence y’ x’
  52. 52. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Two Pulse sequences (II) 90——τ ——180 ——τ —— Spin Echo sequence y’ x’
  53. 53. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Two Pulse sequences (II) 90——τ ——180 ——τ —— Spin Echo sequence y’ x’
  54. 54. Basic Spin Echo Imaging 54 Part III Physics: Medical Physics Option Magnetic Resonance Imaging T2 and T2 * e -t/ T2 * e -t/ T2 H O H H O H
  55. 55. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Spin-Spin Relaxation Time Static inhomogeneities refocussed by 180 pulse Time varying imhomogeneity are not T2 changes in disease give rise to diagnostic value of MRI
  56. 56. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Bloch Equations
  57. 57. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Superconducting Magnet Helium vessel containing super- con coil Vacuu m
  58. 58. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Superconducting Magnet Bore B0 100cm 0 4T 80cm 0 8T
  59. 59. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Shimming
  60. 60. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Other Magnet Types Permanent magnet, e.g. light weight rare earth magnets, <0.3T
  61. 61. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Other Magnet Types
  62. 62. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Other Magnet Types Electromagnet <0.3T
  63. 63. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Special Superconducting Magnets Active Shielding – Extra coils reduce stray field – Improves siting 10 12 4 2 5mT contour 0.5T wholebody 3T AS wholebody
  64. 64. Part III Physics: Medical Physics Option Magnetic Resonance Imaging RF Coils Remember Brf must be  B0 Field is  subject, can use solenoid.
  65. 65. Part III Physics: Medical Physics Option Magnetic Resonance Imaging RF Coils Remember Brf must be  B0 Field is  subject, cannot use solenoid. Saddle coil, Brf is  coil access. Efficiency is low, and homogeneity is poor
  66. 66. Part III Physics: Medical Physics Option Magnetic Resonance Imaging
  67. 67. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Lecture Content Lecture II – How does NMR become MRI – Effects of Magnetic Field Gradients – Imaging pulse sequences – contrast – examples
  68. 68. Part III Physics: Medical Physics Option Magnetic Resonance Imaging How to Make Images Impose (separately): δBz δx δBz δy δBz δz X gradient Gx Y gradient Gy Z gradient Gz Typical values are 10-100 mT/m
  69. 69. Part III Physics: Medical Physics Option Magnetic Resonance Imaging How to make images For a Z gradient -hz +hz ωz = -γ(B0 + Gz.z)
  70. 70. Part III Physics: Medical Physics Option Magnetic Resonance Imaging How to make images
  71. 71. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Imaging Gradients Special coils (together with power supplies) provide linear variation in B0 in X, Y and Z directions Z B0Z
  72. 72. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Imaging Gradients Special coils (together with power supplies) provide linear variation in B0 in X, Y and Z directions X,Y
  73. 73. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Selection of Slice Use Fourier relationship: RF Amplitude (volts)
  74. 74. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Selection of slice Slice thickness adjusted by changing gradient strength or slice bandwidth (longer pulse has narrower frequency spread) Slice position adjusted by changing the centre frequency of the pulse
  75. 75. Part III Physics: Medical Physics Option Magnetic Resonance Imaging k-space k-space is the raw data space before fourier transformation into the image 2D image will be represented by a 2D array of data points spread throughout k-space Differing the k-space trajectory will alter image contrast
  76. 76. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Image vs k-space ρ(r) S(k )k(t)=
  77. 77. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Image vs k-space ρ(r) S(k )
  78. 78. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Image vs k-space ρ(r) S(k )
  79. 79. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Image vs k-space ρ(r) S(k )
  80. 80. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Image vs k-space ρ(r) S(k ) FT
  81. 81. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Information in k-space
  82. 82. Part III Physics: Medical Physics Option Magnetic Resonance Imaging GE k-space trajectory ρ(r) S(k ) RF G S G R G P S(t)
  83. 83. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr GE k-space trajectory
  84. 84. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr GE k-space trajectory
  85. 85. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE k-space trajectory
  86. 86. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE k-space trajectory
  87. 87. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE k-space trajectory
  88. 88. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE k-space trajectory
  89. 89. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE k-space trajectory
  90. 90. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE k-space trajectory
  91. 91. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE k-space trajectory
  92. 92. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE k-space trajectory
  93. 93. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE k-space trajectory
  94. 94. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE k-space trajectory
  95. 95. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE k-space trajectory
  96. 96. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE k-space trajectory
  97. 97. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE k-space trajectory
  98. 98. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE k-space trajectory
  99. 99. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE k-space trajectory
  100. 100. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE k-space trajectory
  101. 101. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) -kr +kr -kp +kp SE k-space trajectory RF GS GR GP S(t)
  102. 102. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) -kr +kr -kp +kp SE k-space trajectory RF GS GR GP S(t)
  103. 103. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) -kr +kr -kp +kp SE k-space trajectory RF GS GR GP S(t)
  104. 104. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) -kr +kr -kp +kp SE k-space trajectory RF GS GR GP S(t)
  105. 105. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) -kr +kr -kp +kp SE k-space trajectory RF GS GR GP S(t)
  106. 106. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) -kr +kr -kp +kp SE k-space trajectory RF GS GR GP S(t)
  107. 107. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Definitions RF GS GR GP S(t) TR
  108. 108. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Definitions RF GS GR GP S(t) TE
  109. 109. Part III Physics: Medical Physics Option Magnetic Resonance Imaging 1 2 3 4 5 6 T1 1 2 3 4 5 6 T2 Controlling contrast
  110. 110. Part III Physics: Medical Physics Option Magnetic Resonance Imaging 1 2 3 4 5 6 T1 1 2 3 4 5 6 T2 Proton Density TR TE
  111. 111. Part III Physics: Medical Physics Option Magnetic Resonance Imaging 1 2 3 4 5 6 T1 1 2 3 4 5 6 T2 T2 Contrast TR TE
  112. 112. Part III Physics: Medical Physics Option Magnetic Resonance Imaging PD- T2 weighted with full coverage TR 6055, TEeff 20 & 120, ETL = 10, 512x240, 35.84 x 16.8. 27 5mm slices. Scan time 5mins >360 acquired this year Work horse scan for screening Could contrast, better deep grey matter than FSE at 1.5T
  113. 113. Part III Physics: Medical Physics Option Magnetic Resonance Imaging 1 2 3 4 5 6 T1 1 2 3 4 5 6 T2 T1 Contrast TR TE
  114. 114. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Alzheimer’s
  115. 115. Part III Physics: Medical Physics Option Magnetic Resonance Imaging 1 2 3 4 5 6 T1 1 2 3 4 5 6 T2 * T2 * Contrast TR TE
  116. 116. Part III Physics: Medical Physics Option Magnetic Resonance Imaging T2 and T2* of acute head injury
  117. 117. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Effect of Flip angle α X’ Y’ B0 Brf
  118. 118. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Effect of Flip angle α X’ Y’ B0 Brf 90o pulse Maximum signal but have to wait 5T1 for recovery
  119. 119. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Effect of Flip angle α X’ Y’ B0 Brf
  120. 120. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Effect of Flip angle α X’ Y’ B0 Brf Flip angle 30o: detect M0sin α = 0.5 M0 remaining M0cos α = 0.87 M0
  121. 121. Part III Physics: Medical Physics Option Magnetic Resonance Imaging TR/TE/ α 41/9/15 500/9/15 41/9/9041/9/60 500/9/90 Contras t versus α Contras t versus TR
  122. 122. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Why does MRI take so long Answer – Only one phase encode line acquired per excitation – Spin Echo: 256*3s for T2, 256*0.6s for T1 – Gradient Echo: 256*35ms (but have to do 3D Solution – get more phase encode lines per excitation
  123. 123. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Pulse sequence RF G1 Gslice G2 Rx Multiple spin echos RARE/FSE/TurboSE
  124. 124. Part III Physics: Medical Physics Option Magnetic Resonance Imaging RARE k-space trajectory -kr +kr -kp +kp
  125. 125. Part III Physics: Medical Physics Option Magnetic Resonance Imaging RARE k-space trajectory -kr +kr -kp +kp
  126. 126. Part III Physics: Medical Physics Option Magnetic Resonance Imaging RARE k-space trajectory -kr +kr -kp +kp
  127. 127. Part III Physics: Medical Physics Option Magnetic Resonance Imaging RARE k-space trajectory -kr +kr -kp +kp
  128. 128. Part III Physics: Medical Physics Option Magnetic Resonance Imaging RARE k-space trajectory -kr +kr -kp +kp
  129. 129. Part III Physics: Medical Physics Option Magnetic Resonance Imaging RARE k-space trajectory -kr +kr -kp +kp
  130. 130. Part III Physics: Medical Physics Option Magnetic Resonance Imaging RARE k-space trajectory -kr +kr -kp +kp
  131. 131. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Echo Planar Imaging Fastest imaging method Typical AQ time is 30-100ms Low RF deposition Very fast gradient switching Highly demanding on MRI hardware – B0 homogeneity – gradient switching
  132. 132. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Why ? freeze involuntary patient motion visualization of dynamic process – fast imaging: minutes – turbo imaging: seconds More complex MRI experiments – obtain multiple images vary some parameter e.g. TI reduce patient examination time
  133. 133. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE-PEI k-space trajectory
  134. 134. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE EPI k-space trajectory
  135. 135. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE EPI k-space trajectory
  136. 136. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE EPI k-space trajectory
  137. 137. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE EPI k-space trajectory
  138. 138. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE EPI k-space trajectory
  139. 139. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE EPI k-space trajectory
  140. 140. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE EPI k-space trajectory
  141. 141. Part III Physics: Medical Physics Option Magnetic Resonance Imaging ρ(r) S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE EPI k-space trajectory
  142. 142. Part III Physics: Medical Physics Option Magnetic Resonance Imaging S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE EPI k-space trajectory
  143. 143. Part III Physics: Medical Physics Option Magnetic Resonance Imaging S(k ) RF G S G R G P S(t) -kr +kr -kp +kp GE EPI k-space trajectory
  144. 144. Part III Physics: Medical Physics Option Magnetic Resonance Imaging GE vs EP Imaging TE ms TR ms AQ ms BW khz Gread mT/m Switch µs GE 10 35 10 25 2.5 500 EPI 50 ∞0.5 250 25 100 Assume FOV 25cm AQ = 10ms Matrix 256 time/sample = 10-2 /256 Bandwidth = 25kHz Gread = 25 x 103 /0.25 = 100 000Hz/m = ~ 2.5 mT/m
  145. 145. Part III Physics: Medical Physics Option Magnetic Resonance Imaging GE vs EP Imaging TE ms TR ms AQ ms BW khz Gread mT/m Switch µs GE 10 35 10 25 2.5 500 EPI 50 ∞0.5 250 25 100 Assume FOV 25cm AQ = 0.5ms Matrix 128 time/sample = 5x10-4 /128 Bandwidth = 250kHz Gread = 250 x 103 /0.25 = 1 000 000Hz/m = ~ 25 mT/m
  146. 146. Part III Physics: Medical Physics Option Magnetic Resonance Imaging MRI at 3T 128x128 single shot, GE echo planar. X,Y,Z shim only (~30s) No template or navigator correction Straight FFT after row reversal
  147. 147. Part III Physics: Medical Physics Option Magnetic Resonance Imaging fMRI (functional MRI) Monitor T2 or T2* contrast during cognitive task eg acquire 20-30 slices every 4 seconds Design experiment to have alternating blocks of task and control condition Look for statistically significant signal intenisty changes correlated with task blocks
  148. 148. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Echo-Planar fMRI response stimulus GE-images with EPI fMRI correlation maps Signal response averaged over region  
  149. 149. Part III Physics: Medical Physics Option Magnetic Resonance Imaging oxyhaemoglobin deoxyhaemoglobin Resting O2 & glucose
  150. 150. Part III Physics: Medical Physics Option Magnetic Resonance Imaging O2 & glucose Blood flow ‘over-compensation’ %O2 Activated ATP ADP BOLD signal
  151. 151. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Effect of Intravascular Oxygenation level Blood vessel Paramagne tic T2 (and T2 * ) reduced because of diffusion through field gradients Diamagnet ic deoxy oxy
  152. 152. Part III Physics: Medical Physics Option Magnetic Resonance Imaging T2* curves activated and rest time (ms) signal activated rest TE Signal difference ~ 1-5 % oxyhaemoglobin deoxyhaemoglobin resting activated
  153. 153. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Unilateral Finger Opposition (high res)
  154. 154. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Definitions Diffusion relates to the microscopic Brownian thermal motion of molecules Perfusion, classically is defined as that process that results in the delivery of nutrients to cells, normally expressed as ml/min/100g wet weight of tissue
  155. 155. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Effect of Diffusion on NMR Rms. of an ensemble is zero For a single molecule diffusion results in a gaussian distribution of displacements r
  156. 156. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Diffusion and Spin echoes δ δ ∆
  157. 157. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Diffusion and Spin echoes I/I0 = e -bD b = γ2 g2 δ2 (∆-δ/3)
  158. 158. Part III Physics: Medical Physics Option Magnetic Resonance Imaging D and ADC 0 2 4 6 8 10 0 500 1000 1500 water DMSO I/I0 = e -bD b = γ2 g2 δ2 (∆-δ/3) H2O = 2.1 x 10 -3 mm2 s-1 DMSO = 0.55 x 10 -3 mm2 s-1 normal = 0.71 x 10 -3 mm2 s-1 ischaemic = 0.55 x 10 -3 mm2 s-1 b Log(I/I0)
  159. 159. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Diffusion Weighted Imaging RF G sG rGp
  160. 160. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Diffusion Weighted Imaging RF G sG rGp Gdiffusion
  161. 161. Part III Physics: Medical Physics Option Magnetic Resonance Imaging δ δ ∆ 0 2 4 6 8 10 0 500 1000 1500 water DMSO Typical Values: δ = 20, ∆ = 50 Gmax b 0.5 31 1 124 5 3104 10 12418 b Log(I/I0)
  162. 162. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Practical Problems in Human DWI Gross Motion – Head motion – breathing Pulsitility – CSF/brain pulsation Anisotropy – D is direction dependant, especially white matter
  163. 163. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Practical Problems in Human DWI Gross Motion – Echo Planar Imaging – navigator echoes Pulsitility – gating plus navigator echoes Anisotropy – Measure trace, Dxx + Dyy + Dzz – Measure full tensor (all matrix elements)
  164. 164. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Diffusion Weighted EPI (b=1570 s/mm2 ) READ PHASE SLICE FOV 25cm, TE 118ms TY DW-EPI 128x128 interpolated to 256x256 Partial k-acquisition (62.5%) 4 interleaves, δ = 28ms ; ∆ = 66 ms
  165. 165. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Cambridge NIH van Zijl ADCtrace Diffusion Weighted EPI (b=1570 s/mm2 )
  166. 166. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Diffusion Weighted EPI (b=1570 s/mm2 )AnistropyIndex
  167. 167. Part III Physics: Medical Physics Option Magnetic Resonance Imaging MRI and O15 water PET
  168. 168. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Gadolinium blous experiment in rat brain Imagenumber(relativetoblousinjection) -20 -10 0 10 20 30 40 50 60 Relaxationratechange(s-1) -1 0 1 2 3 4 5 6
  169. 169. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Effect of Intravascular Gd Blood vessel Tissue Tissue
  170. 170. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Effect of Intravascular Gd Blood vessel Tissue Tissue T2 (and T2 * ) reduced because of difussion through field gradients
  171. 171. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Gadolinium blous experiment in rat brain Imagenumber(relativetoblousinjection) -20 -10 0 10 20 30 40 50 60 Relaxationratechange(s-1) -1 0 1 2 3 4 5 6
  172. 172. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Data Analysis Fit first pass of the bolus (avoid recirculation) Gamma variate, or (better) Monte Carlo Estimate arterial input function from large vessel signal rrCBV, rrCBF but absolute MTT
  173. 173. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Perfusion weighted MRI of a patient with a high grade stenosis (>90%) of the right internal carotid artery leading to a terminal supply zone infarction in the region of the middle cerebral artery, from http://www.picker.com/mr/acr/perfusn/perfusn.htm T2 weighted FSE images (3555/80/4) rrCBV-map map of the bolus delay (MTT image)
  174. 174. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Caution Numbers obtained are not for true perfusion (as measured by PET) Similar to dynamic CT, DSC measures micro-capillary flow However good correlation between PET and DSC (in pigs), in humans??
  175. 175. Part III Physics: Medical Physics Option Magnetic Resonance Imaging True Perfusion by MRI Arterial spin labeling – EPISTAR, ASL, QUIPS – label arterial blood on the way into brain – subtract images with and without labelling – difference is due to arterial water that has entered tissue, i.e. perfusion
  176. 176. Part III Physics: Medical Physics Option Magnetic Resonance Imaging Scanner Overview

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