1 Introduction to Magnetic Resonance Imaging ی ک ش ز پ ک ی ز ی ف ز پ ه ای م د ق م درسSahand University of Technology Faculty of Electrical Engineering M. Shamsi
Jan 03, 2016
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Introduction to Magnetic Resonance Imaging
درس مقدمه ای بر فیزیک پزشکی
Sahand University of Technology
Faculty of Electrical Engineering
M. Shamsi
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Magnetic Resonance Imaging
• Non-invasive medical imaging method, like ultrasound and X-ray.
• Clinically used in a wide variety of specialties.
Abdomen Spine Heart / Coronary
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Magnetic Resonance Imaging
Advantages:• Excellent / flexible contrast• Non-invasive• No ionizing radiation• Arbitrary scan plane
Challenges:• New contrast mechanisms • Faster imaging
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Topics
• MRI Physics
• Hardware
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Topics
• MRI Physics
• Hardware
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Magnetic Resonance
• Certain atomic nuclei including 1H exhibit nuclear magnetic resonance.
• Nuclear “spins” are like magnetic dipoles.
1H
MRI Physics
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Polarization
• Spins are normally oriented randomly.
• In an applied magnetic field, the spins align with the applied field in their equilibrium state.
• Excess along B0 results in net magnetization. No Applied Field Applied Field
B0
MRI Physics
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MRI Physics
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Static Magnetic Field
Longitudinal
Transverse
B0
z
x, y
MRI Physics
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Precession
• Spins precess about applied magnetic field, B0, that is along z axis.
• The frequency of this precession is proportional to the applied field:
B
MRI Physics
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Relaxation
• Magnetization returns exponentially to equilibrium:• Longitudinal recovery time constant is T1
• Transverse decay time constant is T2
• Relaxation and precession are independent.
Precession Decay Recovery
MRI Physics
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Signal Reception• Precessing spins cause a change in flux () in
a transverse receive coil.
• Flux change induces a voltage across the coil.
Signal
y
x
B0
z
MRI Physics
Origin of the MR Signal
Before Excitation
After Excitation
Excitation tips the net magnetization (M) down into the transverse plane, where it can generate current in detector coils.
During Excitation (to)
During Excitation (t1)
The amount of current oscillates at the (Larmor) frequency of the net
magnetization.
MRI Physics
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Topics
• MRI Physics
• Hardware
MRI hardware
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x 60,000 =
The Big MagnetMain field = B0
• Continuously on
• Very strong : Earth’s magnetic field = 0.5 Gauss / 1 Tesla (T) = 10,000 Gauss
3 Tesla = 3 x 10,000 0.5 = 60,000 x Earth’s magnetic field
B0
Robarts Research Institute 3T
MRI hardware
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MRI hardware
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MRI hardware
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MRI hardware
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MRI hardware
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MRI hardware
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At $2 million, the most expensive equipment in the hospital…
MRI hardware
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Superconducting Magnet
MRI hardware
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Resistive Electromagnet
MRI hardware
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Permanent MRI System
MRI hardware
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MRI hardware
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MRI hardware
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MRI hardware
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MRI hardware
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MRI hardware
Head CoilHead Coil
31Head CoilHead Coil
MRI hardware
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RF Receiver Coils
MRI hardware
Three Sets of Gradient Coils
MRI hardware
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GRADIENTS
MRI hardware
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MRI hardware
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MRI hardware
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MRI hardware
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MRI hardware
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MRI hardware
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MRI hardware
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MRI hardware
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MRI hardware
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43Surface CoilsSurface Coils
MRI hardware
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MRI hardware
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MRI hardware
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Exclusion of Various Objects
MRI hardware
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Exclusion of Ferromagnetic Objects
MRI hardware
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Shielding of MRI Room
MRI hardware
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49•Delivery of 1.5T Superconducting MagnetDelivery of 1.5T Superconducting Magnet
MRI hardware
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50• 0.2 T Open MRI with permanent magnet (11 tons)0.2 T Open MRI with permanent magnet (11 tons)
MRI hardware
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51• 0.7 T Open MRI with superconducting magnet0.7 T Open MRI with superconducting magnet
MRI hardware
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52Body Array and Head Array CoilsBody Array and Head Array Coils
MRI hardware
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MRI hardware
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