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
Julio 22, 2005Julio 22, 2005 Imagenología por Resonancia MagnéticaImagenología por Resonancia Magnética
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
Julio 22, 2005Julio 22, 2005 Imagenología por Resonancia MagnéticaImagenología por Resonancia Magnética
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
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Electromagnetic SpectrumElectromagnetic Spectrum
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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
Julio 22, 2005Julio 22, 2005 Imagenología por Resonancia MagnéticaImagenología por Resonancia Magnética
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
Relaxation Time T2Relaxation Time T2
The time constant which describes the return to equilibrium of the transverse magnetization
Mxy = 0
Mz = 0
Julio 22, 2005Julio 22, 2005 Imagenología por Resonancia MagnéticaImagenología por Resonancia Magnética
Chemical Shift
The magnetic field that each nuclei experiment varies according to the type of nuclei and bonds in the molecule
δδ3.5ppm
AguaAguaGrasaGrasa
Relaxation Time T1Relaxation Time T1
The time constant which describes how MZ returns to its equilibrium value
Mz = Mo
Relaxation Time T1, T2Relaxation Time T1, T2
T2 ≤ T1
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Free Induction Decay - FIDFree Induction Decay - FID
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Free Induction Decay - FIDFree Induction Decay - FID
Time DomainTime Domain Frequency DomainFrequency Domain
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FID 90FID 90o o SequenceSequence
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FID 90FID 90o o SequenceSequence
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Spin Echo SequenceSpin Echo Sequence
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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.
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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
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Pulse DiagramPulse Diagram
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Pulse DiagramPulse Diagram
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Julio 22, 2005Julio 22, 2005 Imagenología por Resonancia MagnéticaImagenología por Resonancia Magnética
Pulse DiagramPulse Diagram
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Julio 22, 2005Julio 22, 2005 Imagenología por Resonancia MagnéticaImagenología por Resonancia Magnética
Pulse DiagramPulse Diagram
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Julio 22, 2005Julio 22, 2005 Imagenología por Resonancia MagnéticaImagenología por Resonancia Magnética
Pulse DiagramPulse Diagram
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Pulse DiagramPulse Diagram
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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
Julio 22, 2005Julio 22, 2005 Imagenología por Resonancia MagnéticaImagenología por Resonancia Magnética
Image ProcessingImage Processing