General Concepts 2 min read
Digital Data Processing
A typical scan protocol calls for a sequence of tailored RF and gradient pulses with duration controlled in steps of…
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Radiofrequency Coils
Radiofrequency (RF) coils are components of every scanner and are used for two essential purposes — transmitting and receiving signals…
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Gradient Coils
Three gradient fields, one each for the x, y, and z directions of a Cartesian coordinate system, are used to…
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Fringing Fields
A large, powerful magnet produces a strong magnetic field in the region surrounding it as well as in its interior.…
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Magnetic Field Homogeneity
The necessary degree of spatial uniformity of the field can be achieved only by carefully placing the coils at specific…
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Superconducting Magnets
Since the early 1980s, the use of cryogenically cooled superconducting magnets [Wilson, 1983] has been the most satisfactory solution to…
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Resistive Magnets
The first whole-body scanners, manufactured in the late 1970s and early 1980s, used four to six large coils of copper…
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Permanent Magnets and Electromagnets
Both these magnet types use magnetized materials to produce the field that is applied to the patient. In a permanent…
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Static Field Magnets
The main field magnet [Thomas, 1993] is required to produce an intense and highly uniform, static magnetic field over the…
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Fundamentals of MRI Instrumentation
Three types of magnetic fields — main fields or static fields (B2), gradient fields, an radiofrequency (RF) fields (B1) —…
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Defining Terms
Gyromagnetic ratio γ : An intrinsic property of a nucleus. It determines the Larmor frequency through the relation ω0 = −γ B0 .…
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Contrast Mechanisms
The tremendous clinical utility of MRI is due to the great variety of mechanisms that can be exploited to create…