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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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IR Frequency Region: Fingerprint Region

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IR spectra are divided into two main regions: the diagnostic region and the fingerprint region. The diagnostic region of the spectrum lies above 1500 cm−1. The absorptions resulting from single-bond vibrations of the N–H, C–H, and O–H stretch at higher wavenumbers and appear on the left side of the spectrum. The stretching absorptions of the C≡C and C≡N occur between 2100–2300 cm−1. In contrast, those arising from stretching absorptions of the...

Rectangular and Triangular Pulse Function

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The unit rectangular pulse function is mathematically represented by a rectangular function centered at the origin with a height of one unit. This function is defined by two parameters: T, which specifies the center location of the pulse along the time axis, and τ, which determines the pulse duration.
For example, consider a rectangular pulse with a 5V amplitude, a 3-second duration, and centered at t=2 seconds. This pulse can be expressed using the rectangular function, written as,

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15N CPMG Relaxation Dispersion for the Investigation of Protein Conformational Dynamics on the µs-ms Timescale

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Advancing RF pulse design using an open-competition format: Report from the 2015 ISMRM challenge.

William A Grissom^1,2, Kawin Setsompop³, Samuel A Hurley⁴

¹Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA.

Magnetic Resonance in Medicine

|October 30, 2016

Summary

This summary is machine-generated.

RF pulse design challenges spurred innovation in simultaneous multislice (SMS) and parallel transmission (pTx) MRI. Winners developed significantly shorter pulses for faster, higher-quality imaging.

Keywords:

RF pulse design open challenge optimization parallel transmission selective excitation simultaneous multislice imaging ultra-high field MRI

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Paramagnetic Relaxation Enhancement for Detecting and Characterizing Self-Associations of Intrinsically Disordered Proteins

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Published on: September 23, 2021

Area of Science:

Magnetic Resonance Imaging (MRI)
Radiofrequency (RF) Pulse Design
Medical Imaging Technology

Background:

Simultaneous multislice (SMS) imaging and parallel transmission (pTx) are crucial for accelerating MRI scans.
Designing shorter RF pulses is essential for improving SMS imaging at high multiband factors and for multislice imaging in ultra-high field MRI.
Existing RF pulse design methods face limitations in achieving desired speed and efficiency.

Purpose of the Study:

To foster advancements in RF pulse design for critical MRI applications through a competitive challenge.
To address two key challenges: designing short simultaneous multislice (SMS) refocusing pulses and short slice-selective parallel transmission (pTx) excitation pulses.
To encourage the development of novel pulse design strategies under realistic hardware and safety constraints.

Main Methods:

An open competition with two sub-challenges: SMS refocusing pulse design and pTx excitation pulse design.
Two-phase structure for each sub-challenge, starting with low-barrier problems and progressing to performance-focused solutions.
Realistic hardware and safety constraints were imposed on all pulse designs.

Main Results:

The pTx Challenge yielded a spokes pulse design method achieving 10.6 times shorter pulse durations compared to conventional methods.
The SMS Challenge resulted in a time-optimal control multiband pulse design algorithm that produced pulses 5.1 times shorter than conventional approaches.
Both winning methods significantly outperformed existing techniques in pulse duration reduction.

Conclusions:

The RF pulse design competition accelerated the development of superior solutions for SMS imaging and ultra-high field MRI.
The challenge demonstrated the effectiveness of open competition in driving innovation in RF pulse design.
These advancements pave the way for faster and more efficient MRI acquisition techniques.