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Donald W. McRobbie
Essentials of MRI Safety
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Table of Contents
List of Tables
List of Illustrations
Guide
Pages
Страница 7
Страница 8
Страница 9
Страница 10
1 Systems and safety: MR hardware and fields INTRODUCTION
OVERVIEW OF MRI OPERATION
Nuclear magnetic resonance
Example 1.1 B
1
amplitude
Image formation
Slice selection
In‐plane localization
Pulse sequences
Parallel imaging
Overview of MRI applications
MRI HARDWARE
Magnet system
Superconductivity
Superconducting MR magnets
Short larger‐bore magnets
Other magnets
Imaging gradients subsystem
Example 1.2 Gradient performance
Radiofrequency subsystem
RF transmission
RF reception
ELECTROMAGNETIC FIELDS
Static field
Definition of magnetic flux density and the tesla
MYTHBUSTER:
B0 fringe field
Fringe field spatial gradient
MYTHBUSTER:
The imaging gradients
Example 1.3 B
z
from a gradient
Example 1.4 Gradient dB/dt
Radiofrequency field
MYTHBUSTER:
B1+ and B1+rms
Scanning modes
OTHER MEDICAL DEVICES
CONCLUSIONS
Revision Questions
References
Further reading and resources
Notes
2 Let’s get physical: fields and forces BASIC LAWS OF MAGNETISM
Understanding Maxwell’s Equations
Electrical charge and electric fields
Magnetic fields
Electromagnetic induction
Electromagnetic waves
Generating magnetic fields
B field from a long straight conductor
B field from loop conductors
B field from a solenoidal coil
B field from a shielded MRI magnet
Spatial dependence of magnetic fields
MAGNETIC MATERIALS
Ferromagnetism
Demagnetizing field and factors
MYTHBUSTER:
Example 2.1 Magnetization of a nickel coin
Example 2.2 Iron rod in the fringe field
FORCES AND TORQUE
Translational force: non‐ferromagnetic materials
MYTHBUSTER:
Example 2.3 Force on a diamagnetic object
Translational force: ferromagnetic objects
Force on a soft unsaturated ferromagnetic material
Example 2.4 Force on an unsaturated ferromagnetic object
MYTHBUSTER:
Soft saturated ferromagnetic material
Permanent magnet
Example 2.5
Force on a ferromagnetic object aligned with B
0
Example 2.6 Force on a ferromagnetic object side on to B
0
Projectile velocity
Torque
Torque on diamagnetic and paramagnetic objects
Example 2.7 Torque on a weakly ferromagnetic magnetic implant
MYTHBUSTER:
Torque on soft ferromagnetic objects
MYTHBUSTER:
Example 2.8 Torque on a ferromagnetic cylinder
Torque v translational force
Forces on circuits
Force on a straight conductor
Example 2.9 Force on an electrical wire
LORENTZ AND HYDRODYNAMIC FORCES
Lorentz force
Magneto‐hydrodynamic effect
LAWS OF INDUCTION
Faraday induction from the gradients
Induced fields from movement within the static fringe field gradient
Example 2.10 Movement in the fringe field gradient
Lenz’s law
Induction from the radiofrequency exposure
Wave‐like behavior of B
1
Near and far field
MYTHBUSTER:
λ/2 resonant length
MYTHBUSTER:
Example 2.11 RF wavelength at 1.5 T
CONCLUSIONS
Revision Questions
References
Further reading and resources
Notes
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