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Julio 22, 2005 Alejandro Jaramillo Robles Soluciones Globales en Imagenología MRI-DT “MAGNETIC RESONANCE IMAGING PRINCIPLES”

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Julio 22, 2005 Imagenología por Resonancia Magnética Antecedentes MRI is based on the principles of nuclear magnetic resonance (NMR), a spectroscopic technique used to obtain microscopic chemical and physical information about molecules

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Julio 22, 2005 Imagenología por Resonancia Magnética Phisics … Spin …is a fundamental property of nature. Spin comes in multiples of 1/2 and can be + or -. wo or more particles with spins having opposite signs can pair up to eliminate the observable manifestations of spin … two or more particles with spins having opposite signs can pair up to eliminate the observable manifestations of spin

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Phisics… Max Plank a particle can undergo a transition between the two energy states by the absorption of a photon h The energy E of a photon is related to its frequency υ called resoanance frequency, by Plank´s constant h. E= h E= υ h

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Julio 22, 2005 Imagenología por Resonancia Magnética Properties of Spin A particle with a net spin in a magnetic field B, can absorb a photon of a frequency. A particle with a net spin in a magnetic field B, can absorb a photon of a frequency υ. The frequency depends on the gyromagnetic ratio γ of the particle The frequency υ depends on the gyromagnetic ratio γ of the particle = γB υ = γB γ H = 42.58 MHz/T

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Nuclei of interest inMRI Nuclei Unpaired Protons Unpaired Protons Unpaired Neutrons Unpaired Neutrons Net Spin Net Spin Biologic Abundance (MHz/T) (MHz/T) 1H1H1H1H1 0 1/2 0.6342.58 31 P 1 0 1/2 0.002417.25 23 Na 12 3/2 0.0004111.27 14 N 1 1 1 0.0153.08 13 C 0 1 1/2 0.09410.71

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Julio 22, 2005 Imagenología por Resonancia Magnética Electromagnetic Spectrum

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Julio 22, 2005 Imagenología por Resonancia Magnética Energy Level Diagrams E = h γB E = h γB When the energy of the photon matches the energy difference between the two spin states an absorption of energy occurs

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Julio 22, 2005 Imagenología por Resonancia Magnética Energy Level Diagrams E = h γB E = h γB Variable Magnetic Field Constant Frequency Constant Magnetic Field Variable Frecuency

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Spin Packets

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Magnetization Vector

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Net Magnetization

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At Equilibrium Mz = Mo Mxy = 0

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

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Relaxation Time Mz = 0 Mxy ≠ 0

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Relaxation Time T2 Mxy ≠ 0 Mz = 0

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Relaxation Time T2 The time constant which describes the return to equilibrium of the transverse magnetization Mxy = 0 Mz = 0

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Julio 22, 2005 Imagenología por Resonancia Magnética Chemical Shift The magnetic field that each nuclei experiment varies according to the type of nuclei and bonds in the molecule δ 3.5ppmAguaGrasa

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Relaxation Time T1 The time constant which describes how MZ returns to its equilibrium value Mz = Mo

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Relaxation Time T1, T2 T2 ≤ T1

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Julio 22, 2005 Imagenología por Resonancia Magnética Free Induction Decay - FID

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Julio 22, 2005 Imagenología por Resonancia Magnética Free Induction Decay - FID Time Domain Frequency Domain

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Julio 22, 2005 Imagenología por Resonancia Magnética FID 90 o Sequence

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Julio 22, 2005 Imagenología por Resonancia Magnética FID 90 o Sequence

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Julio 22, 2005 Imagenología por Resonancia Magnética Spin Echo Sequence

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Julio 22, 2005 Imagenología por Resonancia Magnética 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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Julio 22, 2005 Imagenología por Resonancia Magnética Gradient is a variation in the magnetic field with respect to position …is a variation in the magnetic field with respect to position = γB υ = γB Each region experience a unique magnetic field

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Julio 22, 2005 Imagenología por Resonancia Magnética Pulse Diagram t

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Julio 22, 2005 Imagenología por Resonancia Magnética Pulse Diagram t

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Julio 22, 2005 Imagenología por Resonancia Magnética Pulse Diagram t

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Julio 22, 2005 Imagenología por Resonancia Magnética Pulse Diagram t

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Julio 22, 2005 Imagenología por Resonancia Magnética Pulse Diagram t

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Julio 22, 2005 Imagenología por Resonancia Magnética Pulse Diagram t

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Julio 22, 2005 Imagenología por Resonancia Magnética Image Processing MR – Back Projection one-dimensional field gradient is applied at several angles, and the NMR spectrum is recorded for each gradient

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Julio 22, 2005 Imagenología por Resonancia Magnética Image Processing

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