An introduction to nuclear magnetic resonance imaging - PowerPoint PPT Presentation

Loading...

PPT – An introduction to nuclear magnetic resonance imaging PowerPoint presentation | free to download - id: 29c473-Mjg1M



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

An introduction to nuclear magnetic resonance imaging

Description:

An introduction to nuclear magnetic resonance imaging – PowerPoint PPT presentation

Number of Views:1468
Avg rating:3.0/5.0
Slides: 120
Provided by: yvesde5
Learn more at: http://www.ecnurad.ugent.be
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: An introduction to nuclear magnetic resonance imaging


1
An introduction to nuclear magnetic resonance
imaging
Biomedical signals and images
Part 2
prof. Yves De Deene Research group quantitative
MRI / MEDISIP
2
In previous lecture ...
3
In previous lecture ...
The NMR signal
B0
Hydrogen proton transmits a radiofrequent
electromagnetic wave (yellow) after excitation
by an RF pulse (red)
EXCITATION PULSE
B0
Image Processing (2D-FFT)
Cross-section of an NMR scanner
4
In previous lecture ...
From signal to image formation T1 and T2 decay
Gradient coils
Radiofrequency coil
Cryogenic magnet
5
In previous lecture ...
W g. B
Nuclear Magnetic Resonance Imaging Dephasing
T2 decay
In free space
In human tissue
6
First NMR experiments in vivo
1972
W g. B
Resonance condition fulfilled
Raymond V. Damadien
Inhomogeneous magnetic field
First MRI scan
7
Early NMR imagers with spatial encoding
1973 - 1974
8
Spatial encoding in Magnetic Resonance Imaging An
analogon in acoustics Localisation of glasses
close together
1
2
3
9
Spatial encoding in Magnetic Resonance
Imaging Slice selection (Analogon in acoustics)
1
2
3
10
Spatial encoding in Magnetic Resonance
Imaging Slice selection
W g. B
GRADIENT COILS
11
Spatial encoding in Magnetic Resonance
Imaging Imaging gradients
12
Spatial encoding in Magnetic Resonance
Imaging Frequency encoding (Analogon in acoustics)
1
2
3
13
Spatial encoding in Magnetic Resonance
Imaging Frequency encoding
14
The spin-echo sequence Basic principle
Erwin Hahn 1949
First discovery of a spin-echo - E. Hahn (1950) -
15
The spin-echo sequence Slice selection
16
The spin-echo sequence Phase encoding
EXCITATION PULSE
17
The spin-echo sequence Frequency encoding
EXCITATION PULSE
18
The spin echo sequence with all gradients
180 PULSE
180 PULS
90 PULSE
90 PULSE
TE/2
TE/2
TE/2
TE/2
GSL
GRO
GPH
19
The spin echo sequence with all gradients (multi
slice)
180 PULSE
180 PULS
90 PULSE
90 PULSE
TR
TE/2
TE/2
TE/2
TE/2
Slice 1
GSL
20
SLICE SELECTION
z
PHASE
(f)
FREQUENCY
(f)
21
The k-space ( time domain)
22
Filling k-space (spin-echo sequence)
with
Phase Encoding Gradient
Spin-echo
23
From k-space to image space
24
Exploring k-space (spatial frequencies)
25
Exploring k-space (partial filling)
Half k-space
Full k-space
k-space
Image space
26
Exploring k-space (partial filling)
Full k-space
k-space
Image space
27
Exploring k-space (resolution)
Full k-space (256 x 256)
k-space
Image space
28
Exploring k-space (spikes)
Full k-space (256 x 256)
k-space
Image space
29
Travelling in k-space (constant gradients)
The velocity in the kx direction is proportional
to the gradient strength Gx
The velocity in the ky direction is proportional
to the gradient strength Gy
if Gx Cte
if Gy Cte
30
Travelling in k-space (constant gradients)
A 180 pulse takes you to a symmetrical point
31
Travelling k-space with a spin-echo sequence
180 PULS
90 PULSE
TE/2
TE/2
GSL
Gz
GRO
Gx
GPH
Gy
32
Travelling k-space with a spin-echo sequence
180 PULS
90 PULSE
TE/2
TE/2
GSL
Gz
GRO
Gx
GPH
Gy
33
Travelling k-space with a spin-echo sequence
180 PULS
90 PULSE
TE/2
TE/2
GSL
Gz
GRO
Gx
GPH
Gy
34
Travelling k-space with a spin-echo sequence
180 PULS
90 PULSE
TE/2
TE/2
GSL
Gz
GRO
Gx
TR
GPH
Gy
Imaging time TR.Nph.NEX
Number of phase lines
Number of exposures
Repetition time
35
Evolution of gradient systems
1985
10 mT/m 500 ?s (20 mT/m/ms)
1995
25 mT/m 250 ?s (100 mT/m/ms)
2000
40 mT/m 400 ?s (100 mT/m/ms)
36
Travelling k-space in a fast manner Echo Planar
Imaging (EPI)
90 PULSE
GRO
Gx
GPH
Gy
Imaging time TR. NEX
37
Travelling k-space in a fast manner Spiral
scanning
90 PULSE
GRO
Gx
GPH
Gy
Imaging time TR. NEX.Nsp
Number of spirals
38
Travelling k-space in a fast manner Projection
acquisition
180 PULS
90 PULSE
TE/2
TE/2
GSL
Gz
GRO
Gx
GPH
Gy
39
Travelling k-space in a fast manner Projection
acquisition
180 PULS
90 PULSE
TE/2
TE/2
GSL
Gz
GRO
Gx
C
GPH
Gy
B
A
B,C
40
Travelling k-space in a fast manner Projection
acquisition
y
s
x
P(?,s)
41
Spatial versus time domain Measurement parameters
k-space
Image space
FFT
Tacq
FOVx
Nx samples per acquisition time
Nx samples over FOVx
(typical value fs 32 kHz)
Ts
Bandwidth per pixel (!)
42
Sampling of k-space
k-space Time domain
Image space Fourier domain
43
Sampling of k-space Undersampling
k-space Time domain
Image space Fourier domain
Time Signal
Frequency Signal
t
f
Fourier transform of Dirac comb
Shah function or Dirac comb
1/Ts
t
f
Ts
Sampled time signal
f
t
44
Sampling of k-space Nyquist Shannon sampling
theorem
T
If a function f(t) contains no frequencies higher
than f ( 1/T), it is completely determined by
sampling the function with a sampling frequency
fs gt 2.f.
45
Sampling of k-space Nyquist Shannon sampling
theorem
k-space Time domain
Image space Fourier domain
Time Signal
t
46
Undersampling of k-space Aliasing artifact
Image space Fourier domain
Frequency Signal
f
Fourier transform of Dirac comb
1/Ts
f
f
47
MR sequences
Which sequence? What contrast?
T2
T1
PACE
SPRITE
SSFP
TOMROP
PHAPS
CE-FAST
FLOW
IR-SE
CPMG
FISP
PSIF
FSE
D
SR-SE
SR-MSE
SE
XY-4
FLASH
t-FLASH
RARE
SR-SE
FARM
PRESTO
IR-MSE
?
QUEST
GESSE
IR-FLASH
GRASE
CSI
TRSE
TSE
EPI
EPI
RARE
PURR-DANTE
ISIS
HASTE
FLAIR
PURR-TURBO
MT
T1?
48
Image contrast Spin echo sequence
180
180
FA
TR
TE/2
TE/2
Mz,nFA-
49
Image contrast Spin echo sequence
180
FA
TR
TE/2
TE/2
Meq
Mz,n?-
Mz,nFA-
Meq
FA
Mz,n?
Mz,nFA
Mx,nEcho
Mx,nFA
Mz,nEcho
Mz
Mz
50
Image contrast Spin echo sequence
51
Image contrast Spin echo sequence
52
Simulations of imaging sequences Rotation matrices
Static magn. field
Magn. field inhomogen.
Magn. field gradients
RF pulse
M (t)
Mz (t?t)
M (t?t)
Mx (t?t)
B1(t)
53
Image quality SNR Measurement time Spatial
resolution
SCANNING SEQUENCE
54
Image quality Imaging artifacts
GEOMETRICAL DISTORTIONS
INTENSITY VARIATIONS
SCANNER RELATED
OBJECT RELATED
SCANNER RELATED
OBJECT RELATED
  • Magnetic field
  • inhomogeneities
  • B0(x,y,z)
  • Temperature
  • drift
  • Molecular
  • self-diffusion
  • Gradient-
  • inhomogeniteities
  • g(x,y,z)
  • Standing waves
  • Eddy currents
  • DB0 (t), Dgx,y,z (t)

55
Imaging artifacts DC offset
Quadrature detector
Re
To ADC
Low Pass FILTER
RF signal
PreAmp
0
Im
To ADC
Low Pass FILTER
90
56
Imaging artifacts Quadrature ghost
Quadrature detector
Re
To ADC
Low Pass FILTER
RF signal
PreAmp
0
Im
To ADC
Low Pass FILTER
90
57
Imaging artifacts Gradient and magnetic field
inhomogeneities
58
Imaging artifacts Gradient and magnetic field
inhomogeneities
Eddy currents
59
Imaging artifacts Gradient and magnetic field
inhomogeneities Eddy currents effect on slice
position
Offset in main magn. field during slice selection
Offset in main magn. field during frequency
encoding
Gradient. during freq. encoding
Gradient during slice selection
DB0(t)
DB0(t)
gSL
Gsl
Gsl
gRO
GRO
GRO
60
Imaging artifacts Gradient and magnetic field
inhomogeneities
Susceptibility differences
Susceptibility artifact caused by a dental
prothesis (SAG en TRA)
Susceptibility artifact caused by a screw
61
Imaging artifacts Gradient and magnetic field
inhomogeneities
Susceptibility differences
Field lines in a homogeneous medium
Field lines in medium containing a paramagnetic
substance
62
Imaging artifacts Motion artifacts
63
Imaging artifacts Motion artifacts
Synthetic blob phantom (and corresponding k-space
  • Sequence parameters
  • Tacq 7.680 ms
  • TR 1 s
  • MS 128 x 128
  • Tmeas 2 min. 8 s

Fast motion within the acquisition of a phase
line (T lt Tacq)
Slow motion within the sampling of different
phase lines (T gt TR)
64
Imaging artifacts Motion artifacts
65
Imaging artifacts RF Inhomogeneity
Different RF coils... Different field
homogeneity
Scan with spine coil
RF shielding by dental implant
66
Imaging artifacts Flow
180 PULS
90 PULSE
TE/2
TE/2
GSL
Gz
GRO
Gx
67
Quality assurance Multi-purpose QA phantom
RESOLUTION
SNR
SLICE PROFILE
SPATIAL DISTORTION
GHOST ARTIFACTS
GHOST ARTIFACTS
SLICE WARP
IMAGE CONTRAST
68
The first MRI scanners ...
Open MRI unit
Interventional MRI unit
Mobile MRI unit
and the recent ones
69
Anatomical imaging Multiple sclerosis
T2 weighted (transverse)
T1 weighted With contrastagent
Proton density (transverse)
Proton density (sagital)
Cluster analysis (T1w, T2w, PDw)
70
Anatomical Imaging Arterio venous diseases
71
Anatomical imaging Oncology
T2 weighted (cyst)
T1 weighted with contrastagent (Breast carcinoma)
T1 weighted (Brain metastasis)
T2 weighted (chondrosarcoma)
T2 weighted (cervix carcinoma)
T2 weighted (prostate tumor)
72
Anatomical imaging Bone and soft tissue
rheumatoid arthritis whrist
rheumatoid arthritis knee
T2 weighted (torn ligaments)
T2 weighted (hernia)
Osteoporosis (femur)
73
But there is more to MRI than anatomical imaging
...
2008
1972
State of the art
  • 3D images
  • dynamic images
  • sharp image resolution

First NMR images
74
MRI thermometry
MRI elastography
45C
TUMOR
40C
35C
30C
Anatomical MR image
MR temparature map
Transducer (100 Hz 1000 Hz)
Proton Resonance Frequency (PRF) method
Hard gel
Soft gel
75
Quantitative microstructure analysis Foam and
lung tissue
Numerical simulation
?g
?b
Lung tissue
MAGNETIC FIELD DISTRIBUTION
Gelatin foam
76
NMR perfusion imaging
Normal blood vessels
Tumor bloodvessels
77
NMR perfusion imaging Angiogenesis
Dynamic contrast enhanced MRI (DCE MRI)
Uptake
Clearance
Relative intensity
2 min
4 min
6 min
8 min
10 min
12 min
time
78
NMR imaging of vascularization
TE/2
TE/2
180 Refocusing pulse
90 excitation pulse
Signal
B T
B T
B T
B T
79
NMR imaging of bloodflow
Phase images in three orthogonale directions
Reconstructed flow image
Bloodflow in the left ventrikel of a patient
with dilated heart
Velocity vectors
80
Neurological functional imaging (fMRI)
Red blood cell with oxy-haemoglobine
Red blood cell with deoxy-haemoglubine
PARAMAGNETIC
DIAMAGNETIC
T2 ltlt
T2 gt
81
Neurological functional imaging
Different possible stimuli with fMRI
Motor cortex
Somato- sensorische cortex
Functional images of a blind person during
Braille reading
82
Neurological functional imaging Paradigm setup
Block design
Event-related design
Feet
Feet
Rest
Rest
Rest
time
time
baseline
activation
baseline
activation
Hands
e.g. Interactive paradigms
Feet
Feet
Rest
Rest
time
baseline
activation
e.g. motor paradigms, visual paradigms, ...
Habituation ?
83
Neurological functional imaging Signal processing
Different approaches in analysing the data
  • Exploratory approach Independent Component
    Analysis (ICA)
  • Model-based approach t-test and predefined
    model (HRF)
  • General Linear Model Statistical Parametrical
    Mapping (SPM)

REALIGNMENT
NORMALIZATION
Realignment parameters
120 volumes
Statistical analysis (SPM)
84
Neurological functional imaging Considerations
Ethical considerations
fMRI ? Neuronal activity
Influencing factors
cafein
structural lesions (compression)
Cerebrovascular malformations
autoregulation (vasodilatation)
drugs
BLOOD FLOW
BLOOD VOLUME
hypoxia
volume status
BOLD
hypercarbia
biophysical effects
anesthesia/ sleep
anemia
smoking
OXYGEN CONSUMPTION
degenerative diseases
85
In vivo NMR spectroscopy
86
In vivo NMR spectroscopy Important metabolites
87
In vivo NMR spectroscopy Single voxel
spectroscopy
STEAM sequence
90 PULSE
90 PULSE
90 PULSE
Echo
Gx
Gy
Gz
88
In vivo NMR spectroscopy Multi voxel spectroscopy
Cho / NAA
Cit / Cho
Multi-voxel spectroscopy (Chemical Shift Imaging)
uses PRESS or STEAM sequences with phase
encoding gradients
89
In vivo NMR spectroscopy Processing steps
90
In vivo NMR spectroscopy Processing steps
Water suppresion (CHESS preparation pulse)
In human brain 70 water at a concentration of
55.6 M
72 mol/l H from H2O !!!
metabolite concentrations in brain
0.001 0.01 mol/l H
7200 72000 times lower signal
91
In vivo NMR spectroscopy Processing steps
92
In vivo NMR spectroscopy From semi-quantitative
to quantitative metabolite mapping
93
In vivo NMR spectroscopy in the prostate Quality
control
Prostate test phantom
Fat layer (oil)
Prostatic fluid
Rectum (hole for ER probe)
Agar gel
Endorectal coil
94
In vivo NMR spectroscopy in the
prostate Multi-nuclear spectroscopy
Phosphor-31 (P-31) spectroscopy
(17.25 MHz/T)
PCr
ERGOMETER
Fluor-19 (F-19) spectroscopy
40.08 MHz/T
Applications in drug studies Hypoxia markers
F-MISO
95
Diffusion tensor imaging Fiber tractography
96
Diffusion tensor imaging Fiber tractography
Synthetic fiber bundle
Head phantom
Fiber tracts of the synthetic fiber bundle
97
Diffusion in white matter numerical modelling
Brain white matter (neurons)
Fiber phantom study
2 mm
Numerical simulations Random walk
Interactions
  • Intracellular self-diffusion
  • Extracellular self-diffusion
  • Surface relaxation
  • Permeation through cell wall

D (?,?,TE,G)
Dimensions
  • Radius
  • Spread on radius
  • Density

98
Multi-nuclear imaging Oximetry
19F has nuclear spin1/2
Prototype 19F coils and circuitry
99
Hyperpolarized gas MRI by optical pumping of Rb
Dynamic MRI of the lung
Hyperpolarizer for Helium-3
3D rendered image of human lung
100
Hyperpolarization generator
Polarisation optics
Laser unit
Coil for static magnetic field ( 5 mT)
Cooling circuit
Glass cell (Xe-129, N2, He)
NMR-acquisition
Circulation bath (cooling liquid)
Pre amplifier
PA 100 W
To Spectrometer or scanner
Rb
Oil bath ( 140 C)
Xe-129
He
Pinhole
Circulation bath oil ( 140 C)
Optical spectrometer
N2
Laser power meter
Vacuumpump
Semi-transparant mirror
101
Molecular imaging with MRI
Macromolecular tracers
Hyperpolarization sensitized tracers (HyperCEST)
Lecithine/cholesterol
Perfluoro- octylbromide nanoparticle
(Ultra-)Small-Particle Iron-Oxide SPIO, USPIO
30 nm - 300 nm
Gd-DTPA-PE
Biotinylated DPPE
102
I visited Copenhagen frequently after the war. At
one point, I gave a talk in Copenhagen, and then
afterwards we met with Bjerrum. Bjerrum was a
chemist and a great friend of Niels Bohr Bohr
said to him You know, what these people do is
really very clever. They put little spies into
the molecules and send radio signals to them, and
they have to radio back what they are seeing. I
thought that was a very nice way of formulating
it. That was exactly how they were used. It was
not anymore the protons as such. But from the way
they reacted, you wanted to know in what kind of
environment they are, just like spies that you
send out. That was a nice formulation. -
Felix Bloch -
103
THESIS SUBJECTS 2008 2009
104
Optimization and validation of dynamic contrast
enhanced (DCE) nuclear magnetic resonance (NMR)
imaging in tumors
1.
Normal blood vessels
Tumor bloodvessels
105
Optimization and validation of dynamic contrast
enhanced (DCE) nuclear magnetic resonance (NMR)
imaging in tumors
1.
NMR sequence optimization
Modelling of perfusion
?
Concentration contrast agent
NMR signal intensity
Contrast agent relaxometry
?
Contrast agent molecular environment
Construction of a perfusion phantom
T1, T2 relaxation
106
Development of a non-toxic polymer gel dosimeter
for three-dimensional dose verification in
high-precision radiation therapy
2.
107
Development of a non-toxic polymer gel dosimeter
for three-dimensional dose verification in
high-precision radiation therapy
2.
Problem Current monomers are toxic (carcinogenic)
Acrylamide N,N-methyleen-bis-acrylamide
Can be substituted by non-toxic monomers
Master in de ingenieurswetenschappen biomedische
ingenieurstechnieken Master in de
ingenieurswetenschappen chemische
technologieMaster in de ingenieurswetenschappen
toegepaste natuurkunde
108
Development of a three-dimensional optical
dosimeter for high-precision radiation therapy
3.
Galvo mirror 1 (up down)
109
Development of a three-dimensional optical
dosimeter for high-precision radiation therapy
3.
Problem Light scattering
The solution ? Polyurethane with leucodye

Optimization of dosimeter
Color changes instead of scattering
Master in de ingenieurswetenschappen biomedische
ingenieurstechnieken Master in de
ingenieurswetenschappen chemische
technologieMaster in de ingenieurswetenschappen
toegepaste natuurkunde
110
Characterization of biological tissue by use of
quantitative NMR
4.
Apopthosis programmed cell death
111
Characterization of biological tissue by use of
quantitative NMR
4.
Computer simulations
Generated foam
Calculated Magnetic field map
Maxwell equations
Monte Carlo
DIFFUSION RELAXATION
Calculation of the magnetic field
random walk simulation
Master in de ingenieurswetenschappen biomedische
ingenieurstechnieken Master in de
ingenieurswetenschappen toegepaste natuurkunde
112
Fluor-19 NMR oxygen mapping
5.
Hexafluorobenzene
113
Fluor-19 NMR oxygen mapping
5.
Permeabele capillairen
PFC O2
Influence of molecular environment on the
relaxation behavior ??
19F NMR oxymetrie
Master in de ingenieurswetenschappen biomedische
ingenieurstechnieken Master in de
ingenieurswetenschappen toegepaste natuurkunde
114
Simulation phantom for microwave induced ablation
of cardiac tissue
6.
Problem Distorted electrical stimulation of
heart muscle
BUT ... What about the absorbed thermal heat ??
115
Simulation phantom for microwave induced ablation
of cardiac tissue
6.
Master in de ingenieurswetenschappen biomedische
ingenieurstechnieken Master in de
ingenieurswetenschappen toegepaste natuurkunde
116
Ultrashort TE (UTE) imaging of cortical bone
7.
Conventional MRI
UTE MRI
Cortical bone invisible
Cortical bone visible
UTE (TE 0.08 ms)
(TE 5.66 ms)
Difference image
117
Construction of a benchtop NMR circuit
8.
NMR circuit for hyperpolarization generator
Educative and demonstration purposes
sample
coil
118
Interessante websites
The basics of NMR / MRI (by Hornak) http//www.ci
s.rit.edu/htbooks/nmr/ http//www.cis.rit.edu/htb
ooks/mri/
Magnetic Resonance Technology Information
portal http//www.mr-tip.com
Free online Magnetic Resonance Imaging
course http//www.e-mri.org/index.html
Bloch equation simulations (Brian _at_ Stanford)
Some matlab code http//www-mrsrl.stanford.edu/
brian/bloch/
119
More info athttp//www.ecnurad.ugent.be/QMRI/
About PowerShow.com