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Related Concept Videos

Potential Due to a Magnetized Object01:24

Potential Due to a Magnetized Object

Magnetic dipoles in magnetic materials are aligned when placed under an external magnetic field. For paramagnets and ferromagnets, dipole alignment occurs in the direction of the magnetic field. However, the dipoles align opposite to the field in the case of diamagnets. This state of magnetic polarization due to the external field is called magnetization. Magnetization is defined as the dipole moment per unit volume. It plays a similar role to polarization in electrostatics.
The vector...
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NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences

A pulse is a short burst of radio waves distributed over a range of frequencies that simultaneously excites all the nuclei in the sample. Upon passing a radio frequency pulse along the x-axis, the nuclei absorb energy corresponding to their Larmor frequencies and achieve resonance. This shifts the net magnetization vector from the z-axis toward the transverse plane. This angle of rotation of the magnetization vector, or the flip angle, is proportional to the duration and intensity of the pulse.
Diamagnetism01:26

Diamagnetism

Materials consisting of paired electrons have zero net magnetic moments. However, when these materials are placed under an external magnetic field, the moments opposite to the field are induced. Such materials are called diamagnets. Diamagnetism is the response of the diamagnets when placed in an external magnetic field.
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Paramagnetism01:30

Paramagnetism

Paramagnets are materials with unpaired electrons that possess a finite magnetic moment. In the absence of a magnetic field, these moments are randomly oriented, and thus the net moment is zero. Under an external field, a torque acting on the moments tends to align them along the field's direction. However, the random thermal motion of electrons produces a torque opposite to the external field and tries to disorient the moments. These two competing effects align only a few moments along the...
Magnetostatic Boundary Conditions01:28

Magnetostatic Boundary Conditions

An electric field suffers a discontinuity at a surface charge. Similarly, a magnetic field is discontinuous at a surface current. The perpendicular component of a magnetic field is continuous across the interface of two magnetic mediums. In contrast, its parallel component, perpendicular to the current, is discontinuous by the amount equal to the product of the vacuum permeability and the surface current. Like the scalar potential in electrostatics, the vector potential is also continuous...
Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis,  the precessing magnetic moments are randomly oriented around the z-axis. This...

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Magnetic Resonance Imaging of Multiple Sclerosis at 7.0 Tesla
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Generalized MAGSTE with bipolar diffusion-weighting gradient pulses.

Jürgen Finsterbusch1

  • 1Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, Hamburg, Germany. j.finsterbusch@uke.uni-hamburg.de

Journal of Magnetic Resonance (San Diego, Calif. : 1997)
|June 16, 2009
PubMed
Summary
This summary is machine-generated.

A new method using bipolar gradients enhances the generalized magic asymmetric gradient stimulated echo (MAGSTE) sequence for MRI. This improves diffusion-weighting efficiency, allowing higher b-values without increasing scan time.

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Area of Science:

  • Magnetic Resonance Imaging (MRI)
  • Diffusion MRI
  • Pulse Sequence Design

Background:

  • The generalized magic asymmetric gradient stimulated echo (MAGSTE) sequence is used in MRI to compensate for background gradient cross-terms, particularly in echo-planar imaging.
  • Current MAGSTE sequences have suboptimal efficiency due to reduced gradient amplitudes required for cross-term compensation.

Purpose of the Study:

  • To investigate a modification of the generalized MAGSTE sequence using bipolar gradients to improve diffusion-weighting efficiency.
  • To assess if this modification can achieve higher b-values without extending the echo time.

Main Methods:

  • Replaced single reduced-amplitude diffusion-weighting gradients with two full-amplitude, opposite-polarity bipolar gradients.
  • Maintained cross-term compensation capability by adjusting gradient pulse durations.
  • Evaluated the sequence in phantom and in vivo human brain MR imaging experiments at 3T.

Main Results:

  • The bipolar gradient modification successfully retained cross-term compensation.
  • Achieved significant improvements in diffusion-weighting efficiency, with b-values increasing by 30%–200%.
  • Higher k and b values were obtained without prolonging the echo time.

Conclusions:

  • Bipolar gradients offer a viable method to enhance the efficiency of the generalized MAGSTE sequence.
  • This improvement can increase the applicability of MAGSTE in diffusion MRI, particularly for achieving higher b-values.