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Basics of magnetic resonance imaging (MRI)
Tobias Rudolph
14. Mai 18
Agenda
• Short overview 1. Classic view
– Basics (magnetic dipole momentum, top...) – Signal generation
2. Quantum mechanics 3. Bloch equation 4. Relaxation
– Spin-lattice-relaxation – Spin-spin-relaxation
5. Signals (Free induction decay)
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http://www.medicalexpo.it/prod/canon-medical-system-europe/product-70354-428305.html
Information about MRI
• Body consists of water -> water contains protons -> proton has a spin
• Adventages:
– Not ionising
– 2D and 3D
– Free choice of section
– Change the contrast of soft tissue
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1. Classic magnetic top
Classical – Magnet in constant field
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S
𝐁
N
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Precession– Top in homogeneous field
Magnetic top in magnetic field
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Bz
𝐋
𝐦
Magnetic top in changing field
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Antenna
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Quadrature detector
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2. Quantum mechanics – Nuclear spin
Gyromagnetic ratio
• Magn. dipole momentum:
• Lamor frequency:
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Quantisation
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L
Lz
Bolzmann statistic
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3. Bloch equation
Bloch equations
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Bloch equations after 90°-pulse
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Bloch equations - Solutions
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Spin-lattice-relaxation T1
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Spin-spin-relaxation (dephasing / T2)
biggest B middel B
smallest B
ensemble with ω01 ensemble with ω02 ensemble with ω03
ensemble with ω03
ensemble with ω01
ensemble with ω02
Protons in fat
Protons in water
Protons in lactat
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Spin-spin-relaxation (dephasing / T2)
Some values
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Magnetization after 90°- pulse
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https://en.wikipedia.org/wiki/Nuclear_magnetic_resonance
Free- induction decay (FID)
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Thank you for your attention
Sources
• http://www.rad-diak.de/untersuchungen/ganzkoerper-tumor-screening/
• https://www.trendsderzukunft.de/mrt-mehrfachscans-vermeiden-kontrastmittel-bleibt-im-gehirn/
• http://wswww.physik.uni-mainz.de/F-Praktikum/SS2010/PierreSissol.pdf
• O. Dössel „Bilgebene Verfahren in der Medizin“ 2000
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