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Magnetic Resonance Imaging

Magnetic Resonance Imaging

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...

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.

NMR Spectrometers: Resolution and Error Correction

NMR Spectrometers: Resolution and Error Correction

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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Quantitative Magnetic Resonance Imaging of Skeletal Muscle Disease

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Published on: December 18, 2016

Optimization methods for magnetic resonance imaging gradient waveform design.

Matthew J Middione^1,2, Michael Loecher^1,2, Kévin Moulin^1,2

¹Department of Radiology, Stanford University, Stanford, CA, USA.

NMR in Biomedicine

|April 29, 2020

Summary

This summary is machine-generated.

This study introduces a software solution using numerical optimization for designing magnetic resonance imaging (MRI) pulse sequences. This method creates time-optimal gradient waveforms, enhancing MRI system performance and efficiency.

Keywords:

acquisition methods applications diffusion MR sequences diffusion methods flow imaging methods flow quantitation methods and engineering other applications

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Area of Science:

Medical Imaging
Computational Science

Background:

Designing novel magnetic resonance imaging (MRI) pulse sequences is complex and time-consuming.
Current methods often fail to optimize gradient hardware or mitigate physiological effects, leading to underperforming MRI systems.

Purpose of the Study:

To develop a software solution that integrates numerical optimization into MRI pulse sequence programming.
To enable efficient, time-optimal gradient waveform design that maximizes hardware capabilities and minimizes artifacts.

Main Methods:

Utilizing numerical optimization to incorporate gradient hardware limits and protocol parameters for simultaneous waveform construction.
Applying optimization to design rotational variant vs. invariant waveforms, acceleration-nulled velocity encoding gradients, and diffusion encoding for peripheral nerve stimulation mitigation.
Solving constrained gradient waveform design problems, often convex, on-the-fly within the MRI scanner.

Main Results:

Generated multi-axis, time-optimal gradient waveforms that satisfy design constraints, improving signal-to-noise ratio (SNR)-efficiency.
Demonstrated mitigation of imaging artifacts like eddy currents and accounted for peripheral nerve stimulation.
Enabled easier pulse sequence gradient waveform design with on-the-fly implementation capabilities.

Conclusions:

Numerical optimization offers a powerful approach to streamline and enhance MRI pulse sequence design.
This method leads to more efficient MRI systems that better utilize hardware and reduce artifacts.
The proposed solution facilitates the development and implementation of advanced MRI techniques.