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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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A Simple Stimulatory Device for Evoking Point-like Tactile Stimuli: A Searchlight for LFP to Spike Transitions

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|B1(+)|-selective excitation pulse design using the Shinnar-Le Roux algorithm.

William A Grissom¹, Zhipeng Cao², Mark D Does¹

¹Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA; Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, USA; Vanderbilt University Institute of Imaging Science, Nashville, TN, USA.

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

|March 29, 2014

Summary

This summary is machine-generated.

A novel algorithm designs B1(+)-selective radiofrequency (RF) pulses for magnetic resonance imaging. This method optimizes pulse design for improved slice-selective excitation profiles and reduced off-resonance sensitivity.

Keywords:

RF pulse design Rotating Frame Selective Excitation Selective excitation Shinnar–Le Roux algorithm

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Area of Science:

Magnetic Resonance Imaging (MRI)
Radiofrequency (RF) Pulse Design
Mathematical Modeling

Background:

Accurate radiofrequency (RF) pulse design is crucial for selective excitation in Magnetic Resonance Imaging (MRI).
Existing methods may have limitations in achieving desired excitation profiles and robustness to off-resonance effects.

Purpose of the Study:

To present and validate a new mathematical treatment and algorithm for designing B1(+)-selective RF excitation pulses.
To enable the excitation of large tip-angle slice-selective profiles.
To characterize the performance and robustness of the designed pulses.

Main Methods:

Development of a novel algorithm based on a rotated Shinnar-Le Roux pulse design.
Direct design of the pulse's frequency modulation waveform.
Utilizing amplitude and sign modulation in place of gradient fields.
Experimental validation and simulation-based characterization of pulse performance.

Main Results:

Successful design and validation of B1(+)-selective RF excitation pulses.
Demonstration of a new pulse configuration enabling large tip-angle slice-selective profiles.
Characterization of pulse sensitivity to off-resonance conditions.
Comparison of designed pulses with adiabatic (BIR-4) pulses.

Conclusions:

The presented algorithm offers an effective approach for designing B1(+)-selective RF pulses.
The novel pulse configuration improves slice-selective excitation capabilities.
The method provides a valuable tool for optimizing RF pulse design in MRI applications.