julio 22, 2005 alejandro jaramillo robles soluciones globales en imagenología mri-dt “magnetic...

Julio 22, 2005Julio 22, 2005

Alejandro Jaramillo RoblesAlejandro Jaramillo RoblesSoluciones Globales en Soluciones Globales en

ImagenologíaImagenologíaMRI-DTMRI-DT

““MAGNETIC RESONANCE IMAGING MAGNETIC RESONANCE IMAGING PRINCIPLES”PRINCIPLES”

Julio 22, 2005Julio 22, 2005 Imagenología por Resonancia MagnéticaImagenología por Resonancia Magnética

AntecedentesAntecedentes

MRI is based on the principles of nuclear magnetic resonance (NMR), a

spectroscopic technique used to obtain microscopic chemical and physical

information about molecules


Phisics … SpinPhisics … Spin

……is a fundamental is a fundamental property of nature. property of nature. Spin comes in Spin comes in multiples of 1/2 and multiples of 1/2 and can be + or -.can be + or -.

… two or more particles wo or more particles with spins having with spins having opposite signs can opposite signs can pair up to eliminate pair up to eliminate the observable the observable manifestations of spinmanifestations of spin

Phisics… Max PlankPhisics… Max Plank

a particle can undergo a transition between the two energy states by the absorption of a photon

The energy E of a photon is related to its frequency υ called resoanance frequency, by Plank´s constant hh.

E= E= υ h h


Properties of SpinA particle with a net spin A particle with a net spin in a magnetic field in a magnetic field BB, , can absorb a photon of can absorb a photon of

a frequency a frequency υ. .

The frequency The frequency υ depends on the depends on the

gyromagnetic ratio gyromagnetic ratio γγ of of the particlethe particle

υ = = γγBB

γγHH= 42.58 MHz/T= 42.58 MHz/T

Nuclei of interest inMRINuclei of interest inMRI

Nuclei Nuclei Unpaired Unpaired Protons Protons

Unpaired Unpaired Neutrons Neutrons

Net Spin Net Spin Biologic Biologic

AbundanceAbundance (MHz/T) (MHz/T)

11HH 1 1 0 0 1/2 1/2 0.630.63 42.58 42.58

3131PP 1 1 0 0 1/2 1/2 0.00240.0024 17.25 17.25

2323NaNa 11 2 2 3/2 3/2 0.000410.00041 11.27 11.27

1414NN 1 1 1 1 1 1 0.0150.015 3.08 3.08

1313CC 0 0 1 1 1/2 1/2 0.0940.094 10.71 10.71


Electromagnetic SpectrumElectromagnetic Spectrum


Energy Level DiagramsEnergy Level Diagrams

E = hE = hγγBB

When the energy of the photon matches the energy difference When the energy of the photon matches the energy difference between the two spin states an absorption of energy occursbetween the two spin states an absorption of energy occurs


Energy Level DiagramsEnergy Level Diagrams

E = hE = hγγBB

Variable Magnetic FieldVariable Magnetic Field

Constant FrequencyConstant Frequency

Constant Magnetic FieldConstant Magnetic Field

Variable FrecuencyVariable Frecuency

Spin PacketsSpin Packets

Magnetization VectorMagnetization Vector

Net MagnetizationNet Magnetization

At EquilibriumAt Equilibrium

Mz = MoMz = Mo

Mxy = 0Mxy = 0

Relaxation TimeRelaxation Time

If enough energy is put into the system with a frequency equal to the resonance frequency…

Relaxation TimeRelaxation Time

Mz = 0

Mxy ≠ 0

Relaxation Time T2Relaxation Time T2

Mxy ≠ 0

Mz = 0


The time constant which describes the return to equilibrium of the transverse magnetization

Mxy = 0

Mz = 0


Chemical Shift

The magnetic field that each nuclei experiment varies according to the type of nuclei and bonds in the molecule

δδ3.5ppm

AguaAguaGrasaGrasa


The time constant which describes how MZ returns to its equilibrium value

Mz = Mo

Relaxation Time T1, T2Relaxation Time T1, T2

T2 ≤ T1


Free Induction Decay - FIDFree Induction Decay - FID


Free Induction Decay - FIDFree Induction Decay - FID

Time DomainTime Domain Frequency DomainFrequency Domain


FID 90FID 90o o SequenceSequence


Spin Echo SequenceSpin Echo Sequence


Magnetic Resonance Imaging Magnetic Resonance Imaging

Information generated by a proton in a magnetic field, returning to its equilibrium, after being exposed to a RF signal.


GradientGradient

…is a variation in the is a variation in the magnetic field with magnetic field with respect to positionrespect to position

υ = = γγBB

Each region experience a unique magnetic field


Pulse DiagramPulse Diagram

tt


Image Processing Image Processing

MR – Back ProjectionMR – Back Projection

one-dimensional field one-dimensional field gradient is applied at gradient is applied at several angles, and several angles, and the NMR spectrum is the NMR spectrum is recorded for each recorded for each gradient gradient


Image ProcessingImage Processing

julio 22, 2005 alejandro jaramillo robles soluciones globales en imagenología mri-dt “magnetic...

Documents

h slide

mhzt slide

gradient slide

mo slide

ppmaguagrasa slide

resonance frequency

unique magnetic field

net magnetization slide