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Related Concept Videos

NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences01:17

NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences

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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.
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NMR Spectrometers: Resolution and Error Correction01:14

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When magnetic nuclei in a sample achieve resonance and undergo relaxation, the signal detected in NMR is an approximately exponential free induction decay. Fourier transform of an exponential decay yields a Lorentzian peak in the frequency domain. Lorentzian peaks in an NMR spectrum are defined by their amplitude, full width at half maximum, and position, where the peak width is governed by the spin-spin relaxation time alone. In real experiments, however, the applied magnetic field is rendered...
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Atomic Nuclei: Magnetic Resonance01:05

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The number of nuclear spins aligned in the lower energy state is slightly greater than those in the higher energy state. In the presence of an external magnetic field, as the spins precess at the Larmor frequency, the excess population results in a net magnetization oriented along the z axis. When a pulse or a short burst of radio waves at the Larmor frequency is applied along the x axis, the coupling of frequencies causes resonance and flips the nuclear spins of the excess population from the...
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Magnetic Resonance Imaging01:24

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Magnetic resonance imaging (MRI) is a noninvasive medical imaging technique based on a phenomenon of nuclear physics discovered in the 1930s, in which matter exposed to magnetic fields and radio waves was found to emit radio signals. In 1970, a physician and researcher named Raymond Damadian noticed that malignant (cancerous) tissue gave off different signals than normal body tissue. He applied for a patent for the first MRI scanning device in clinical use by the early 1980s. The early MRI...
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Atomic Nuclei: Nuclear Relaxation Processes01:23

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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.
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Quantitative Magnetic Resonance Imaging of Skeletal Muscle Disease
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Optimal control in a magnetization-prepared rapid acquisition gradient-echo sequence.

Benoît Vernier1,2, Eric Van Reeth1,3, Frank Pilleul1,4

  • 1Univ Lyon, INSA Lyon, Inserm, UCBL, CNRS, CREATIS, UMR5220, U1294, Villeurbanne, France.

NMR in Biomedicine
|September 29, 2023
PubMed
Summary
This summary is machine-generated.

This study introduces a numerical method to optimize magnetization preparation in MP-RAGE sequences for enhanced tissue contrast. The GRAPE algorithm optimizes radio frequency pulses, improving image quality for MRI applications.

Keywords:
Bloch equationsMP-RAGEbrain, contrastoptimal controlpreparation pulses

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Area of Science:

  • Medical Imaging
  • Biophysics
  • Numerical Analysis

Background:

  • Magnetization preparation is crucial for Magnetic Resonance Imaging (MRI) contrast.
  • Optimizing preparation in sequences like MP-RAGE can improve diagnostic accuracy.
  • Existing methods may not fully exploit tissue relaxation time differences.

Purpose of the Study:

  • To develop a numerical framework for optimizing magnetization preparation in 3D MP-RAGE sequences.
  • To enhance achievable contrast between tissues based on relaxation times.
  • To adapt the GRAPE algorithm for cyclic sequences without full recovery.

Main Methods:

  • Utilized an optimal control algorithm (GRAPE) for magnetization preparation.
  • Optimized an arbitrary number of radio frequency pulses within the sequence.
  • Accounted for the steady-state establishment in longitudinal magnetization.
  • Performed numerical simulations and in vitro experiments.

Main Results:

  • Demonstrated an optimized mixed contrast in a traditional T1-weighted sequence.
  • Showcased the versatility of the numerical approach.
  • Acquired example contrasts on brain regions of a healthy volunteer.

Conclusions:

  • The proposed numerical framework effectively optimizes magnetization preparation for enhanced MRI contrast.
  • The method offers improved tissue differentiation in MP-RAGE sequences.
  • Potential applications exist for 3T MRI brain imaging.