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NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences

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.

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Updated: May 28, 2026

Multiplex Chemical Imaging Based on Broadband Stimulated Raman Scattering Microscopy

Multiplex Chemical Imaging Based on Broadband Stimulated Raman Scattering Microscopy

Published on: July 25, 2022

Robust slice-selective broadband refocusing pulses.

Martin A Janich¹, Rolf F Schulte, Markus Schwaiger

¹Technische Universität München, Department of Chemistry, Munich, Germany.

Journal of Magnetic Resonance (San Diego, Calif. : 1997)

|October 7, 2011

Summary

This summary is machine-generated.

New radiofrequency pulses enhance magnetic resonance spectroscopy by improving slice selectivity and reducing errors. These optimized pulses maintain performance across varying B1 amplitudes, outperforming conventional methods.

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Last Updated: May 28, 2026

Multiplex Chemical Imaging Based on Broadband Stimulated Raman Scattering Microscopy

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Published on: July 25, 2022

High-speed Continuous-wave Stimulated Brillouin Scattering Spectrometer for Material Analysis

High-speed Continuous-wave Stimulated Brillouin Scattering Spectrometer for Material Analysis

Published on: September 22, 2017

Area of Science:

Magnetic Resonance Imaging (MRI)
Spectroscopy
Pulse Sequence Design

Background:

Slice-selective refocusing pulses are crucial for localized MR spectroscopy.
Limitations in radiofrequency (RF) pulse bandwidth are constrained by B1 amplitude.
Existing methods like Shinnar-Le Roux (SLR) have limitations in broadband performance and B1 tolerance.

Purpose of the Study:

To design novel slice-selective, broadband refocusing pulses tolerant to B1 amplitude variations.
To investigate the impact of different cost functions on pulse optimization.
To compare the performance of optimized pulses against conventional methods.

Main Methods:

Utilized optimal control theory for numerical pulse design.
Employed a comprehensive study of various cost functions to guide optimization.
Compared optimized pulses with conventional Shinnar-Le Roux (SLR), broadband SLR, and hyperbolic secant pulses.

Main Results:

Optimized pulses demonstrated broadband slice specifications across ±20% B1 scaling in simulations and experiments.
Experimental validation confirmed a threefold reduction in chemical-shift displacement error compared to conventional SLR pulses.
The designed pulses effectively address limitations imposed by B1 amplitude constraints.

Conclusions:

The developed slice-selective broadband refocusing pulses offer improved performance and robustness in localized MR spectroscopy.
These pulses significantly reduce chemical-shift displacement errors, enhancing spectral quality.
The findings suggest a promising advancement for MR spectroscopy applications requiring high spatial accuracy and broadband refocusing.