Active control of the spatial MRI phase distribution with optimal control theory

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Optimal Control Theory
• Pulse Sequence Design

Background:

• Controlling spatial phase distribution in MRI is crucial for advanced imaging techniques.
• Existing methods for RF pulse design have limitations in achieving complex phase patterns.
• Optimal Control (OC) offers a powerful framework for designing sophisticated RF pulses.

Purpose of the Study:

• To investigate the application of Optimal Control theory for designing Radio-Frequency (RF) pulses.
• To achieve active control over the spatial distribution of MRI magnetization phase.
• To generate non-trivial spatial phase patterns for enhanced MRI capabilities.

Main Methods:

• Utilized the Pontryagin Maximum Principle to generate optimized RF pulses.
• Designed pulses to reproduce specific, complex spatial phase patterns in transverse magnetization.
• Validated the designed pulses through numerical simulations (ODIN MRI simulator) and experimental MRI (4.7T small-animal scanner).

Main Results:

• Simulations and experiments successfully demonstrated the ability of OC-designed RF pulses to generate desired spatial phase patterns.
• Phase images obtained from both numerical and experimental tests accurately reflected the targeted phase distributions.
• A practical application showcased the generation of RF pulses for Magnetic Resonance Elastography.

Conclusions:

• Optimal Control theory is a viable method for designing RF pulses that encode information within the MRI magnetization phase.
• OC-designed pulses offer precise control over spatial phase, enabling new possibilities in MRI.
• This approach has potential applications in MRI sequences that rely on phase imaging and advanced contrast generation.