cho cre cit research group quantitative mri in medicine and biology basic mri principles yves de...

ChoCreCit

RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY

Basic MRI principles

Yves De Deene


Nuclear Magnetic ResonanceNMRNMR

MRIMRS MRR

MMagnetic RResonanceSSpectroscopy

MMagnetic RResonance IImaging

MMagnetic RResonanceRRelaxometry

Molecular Composition

Spatial Tissue Differentiation

Molecular Dynamics

Basic MRI principles Yves De Deene



MRIMRS MRR

MMagnetic RResonanceSSpectroscopy

MMagnetic RResonance IImaging

MMagnetic RResonanceRRelaxometry

Spectra Images Relaxation times,Diffusion coefficients

Yves De Deene

NMR imaging is non-invasive

Strong static magnetic field

Radiofrequent electromagnetic waves

Space and time dependent magnetic fields



Yves De Deene

Water

H2O

mp = 1,67.10-24 g

mp = 0,00000000000000000000000167 g

+++++++

++ + qp = 1,6.10-19 C

qp = 0,00000000000000000016 C

Properties of the atomic nucleus



Isidor Isaac RabiZ

N

Z

Z

N

N

H

z

H

z

Spin reservoirovenMolecular beam apparatus



Discovery of nuclear magnetic resonance19381938

In resonance

Off resonance

Yves De Deene

Edward Purcell

IDC

N

S

Electromagnetic wavewith fixed frequency f

Block of parafin

IDC ~ B

Absorption

B

2 fB

B

-1/2

+1/2

E



Nobel price physics (Bloch & Purcell) in 1952

Nuclear magnetic resonance in a block of parafin19461946

Yves De Deene



Nuclear magnetic resonance mathematical descriptionThe Bloch equations19461946

Felix Bloch

L

G

B

Yves De Deene



B

Precession in a magnetic field

Yves De Deene


MRI signal generation

Water molecule

Hydrogen proton transmits a radiofrequent electromagnetic wave (yellow) after excitation by an RF pulse (red)

B0 B0B0

EXCITATION PULSE

COIL

Image Processing(2D-FFT)

Cryogenic magnet

Gradient coils

Radiofrequency transmit/receive coil


Excitation

COILOBJECT:

Spin system

Signal reception

COILOBJECT:

Spin system

MRI signal excitation / reception



Raymond V. Damadien

First MRI scan

Resonance conditionfulfilled

f=B

Inhomogeneous magnetic field

Raymond V. Damadien



The first MRI scanner

19721972

Yves De Deene

Mobile MR unitOpen MR unit

Interventional MR unitClinical MR scanner Animal MR scanner



Current MR scanners

Yves De Deene

MRI signal generationYes, but... what about spatial encoding ??

-1210-910-610-3101310610910

6103101-310-610-910-1210-1510

6103101 910 1210 1510 1810 2110

nuclear

Gamma-rays

X-raysUV

visible

inner

electrons

inner & outer

electrons

outer electrons

molecular vibrations

and rotations

electron spin

nuclear spin

IRTera-hertz

micro-wave

radiofrequency

SH

F

Frequencyf (Hz)

Photon energy E (eV)

EH

F

UH

F

VH

F

HF

MF

LFVLF

ULF

SLF

ELF

Wave length (m)

Interaction with matter

MRI X-ray CT

?



MRI encodingAn analogon in acoustics

1

2

3



MRI encoding: slice selectionAn analogon in acoustics

1

2

3



MRI encoding: Slice selection

64.8 MHz

f = 64.8 MHz

1.52 T

B

z

GRADIENT COILS

z-coil

x-coil

y-coil

patient

X-gradient

Y-gradient

Z-gradient



MRI frequency encodingAn analogon in acoustics

1

2

3

Frequency encoding



MRI frequency encoding

B

B

B

RF COIL

Fouriertransform



Richard Ernst



2D spatial encoding

Yves De Deene

OUT OF PHASE

In free space In human tissue



Dephasing – T2* decay

Yves De Deene

IN PHASE

EXCITATIONPULSE(90°)

The spin-echo sequence

Z

N

TURN BACK !!TE/2 TE/2

REFOCUSSINGPULSE(180°)

EXCITATIONPULSE(90°)

REFOCUSSINGPULSE(180°)

19491949



The spin-echo sequenceSlice selection

SLICE SELECTION

B

z

(90°)

f = 64.8 MHz

1.52 T

1.52 T



The spin-echo sequencePhase encoding

(90°)

PHASE ENCODING

B

y



The spin-echo sequenceFrequency encoding

(90°)

1.43

FREQUENCY ENCODING

B

y

T1.5 1.53

(180°)




TE/2 TE/2

90°PULSE

180°PULS

GSL

GRO

GPH

TE/2 TE/2

90°PULSE

180°PULSE




TE/2 TE/2

90°PULSE

180°PULSE

GSL

TE/2 TE/2

90°PULSE

180°PULSE

fc slice I

TE/2 TE/2

90°PULSE

180°PULSE

GSL

fc+f slice II

fc




SLICE SELECTION

2D-FOURIERTRANSFORM

FREQUENCY AND PHASE ENCODING

AMPLITUDEIMAGE

FREQUENCY

PHASE

z

( , , , ) ( , , , ) ( , , , ) xy x yM x y z t M x y z t j M x y z t

( , , , )0( , , , ) ( , , , ) e j x y z t

xyM x y z t M x y z t

(f)

(f ,

( ) ( , , , )xyV

M t M x y z t dx dy dz



K-space

( , , , )0 ( , , , ) e j x y z t

xyM M x y z t

0

0 0 0

( , , , ) ( ') ' ( ') ' ( ') 't t t

x y zx y z t B t x G t dt y G t dt z G t dt with

0 0

( ) ( )( , ) ( , , ) x yj k t x k t y

x yS k k M x y z z e dx dy

For 2D imaging (z = z0)

0

( ) ( ) ( ).( , , ) ( , , ) x y zj k t x k t y k t z

x y z VS k k k M x y z e dx dy dz For 3D imaging (ignoring relaxation)

S(kx,ky)

0

( ) ( )( , , ) ( , ) x yj k t x k t y

x y x yx y z z C S k k e dk dk

2D FFT

(x,y,z=z0)



K-space

x xk G t

y yk G t

Spin-echo

Phase EncodingGradient

( , , , )0 ( , , , ) e j x y z t

xyM M x y z t 0

0 0 0

( , , , ) ( ') ' ( ') ' ( ') 't t t

x y zx y z t B t x G t dt y G t dt z G t dt with



K-space

FFT

REAL IMAGINARY

MAGNITUDE PHASE

k-space

0 0

( ) ( )( , ) ( , , ) x yj k t x k t y

x yS k k M x y z z e dx dy

REAL IMAGINARY

MAGNITUDE PHASE

Image space

0

( ) ( )( , , ) ( , ) x yj k t x k t y

x y x yx y z z C S k k e dk dk



CBA

Walking through K-spaceThe spin echo sequence

GSL

GRO

GPH

TE/2 TE/2

90°PULSE

180°PULS

= Gx

= Gy

= Gz

D

A

B

C

D

E

E

ky

kx



CBA

Walking through K-spaceThe spin echo sequence

GSL

GRO

GPH

TE/2 TE/2

90°PULSE

180°PULS

= Gx

= Gy

= Gz

D

A

B

C

D

E

E

ky

kx

Imaging time = TR. NEX.Nphase





Spin-lattice and spin-spin decayDipolar interaction

time

B0

time

B0

Spin-spin decay T2Spin-lattice decay T1

Longitudinal relaxation Transverse relaxation

Yves De Deene

INTERMEDIATELAYER

FREEWATER

Hydrogen bridges

C

CO

O

C N BOUNDLAYER+

+ +

+

--

-+

+

- - +

-

- +

+++

Protein, polymer, cell membrane

Low mobility

High mobility

+

M

M

M

t

t

t



Spin-spin decay and molecular dynamics

Yves De Deene

Anatomical imaging:Multiple sclerosis

Proton density(sagital)

T2 weighted(transverse)

T1 weighted With contrastagent

Proton density(transverse)

Cluster analysis (T1w, T2w, PDw)



Anatomical imaging: Multiple sclerosis

Yves De Deene

Anatomical Imaging:Arterio venous diseases

Arterio venous malformation (AVM)

T2 weighted(transverse)

MR angiography

Aneurism

MR angiography MR angiography

Thrombosis

MR angiographyT2 weighted

Infarct (‘stroke’)

Proton density

Proton density

Neck trauma

T2 weighted



Arterio venous diseases

Yves De Deene

Anatomical imaging:Oncology

T2 weighted (chondrosarcoma)

T2 weighted (cyst)

Protondensity(Brain metastasis)

T1 weighted with contrastagent(Breast carcinoma)

T2 weighted(prostate tumor)

T2 weighted (cervix carcinoma)



Oncology

Yves De Deene

Anatomical imagingBone and soft tissue

Osteoporosis (femur)

T2 weighted(torn ligaments)

rheumatoid arthritiswhrist

rheumatoid arthritisknee

T2 weighted(hernia)



Bone and soft tissue

Yves De Deene

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 -

cho cre cit research group quantitative mri in medicine and biology basic mri principles yves de...

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