Localization by nonlinear phase preparation and k-space trajectory design.

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Medical Physics
• Biomedical Engineering

Background:

• Current MRI techniques face challenges in signal localization, particularly at ultra-high fields.
• Selective radiofrequency excitation can be limited by energy deposition and repetition time constraints.

Purpose of the Study:

• To develop and demonstrate a novel technique for localizing MR signals from a target volume.
• To explore the application of local k-space theory in designing spatial encoding for improved localization.
• To provide a practical alternative to selective radiofrequency excitation in specific MRI scenarios.

Main Methods:

• Utilized nonlinear pulsed magnetic fields and custom spatial encoding trajectories based on local k-space theory.
• Applied the technique to simulated phantom and cardiac MRI data with gradient coil phase modulation.
• Acquired in vivo human brain images using a custom quadrupolar gradient coil on a 3-T MRI system.
• Employed various MRI pulse sequences including 3D T2*-weighted spoiled gradient echo, 2D segmented multiple gradient encoded spin echo, and 3D balanced steady-state free precession.

Main Results:

• Successfully demonstrated target localization in phantom and in vivo human brain images.
• The method showed potential for signal localization without relying solely on selective radiofrequency excitation.
• Acquired images using diverse pulse sequences, validating the technique's versatility.

Conclusions:

• The developed technique offers a practical approach for MR signal localization, particularly at ultra-high fields.
• It presents an alternative to selective radiofrequency excitation, especially for steady-state applications requiring minimized repetition time and limited energy deposition.
• Limitations include spatial variations in resolution, aliasing artifacts, and echo times/contrast.