Phase-Relaxed RF Pulse Design for MRI Magnetization
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Solution Overview
Problem
Conventional magnetic resonance imaging (MRI) systems using small-tip-angle (STA) parallel transmission RF pulse designs face limitations such as un-optimized magnitude profiles due to restrictive phase constraints and are primarily suited for small tip angles, making it difficult to accurately design RF pulses for large or arbitrary tip angles.
Innovation Solution
A phase-relaxed, spinor-based optimal control formulation is used to iteratively adjust RF pulse profiles, allowing for the generation of RF pulses with optimal phase profiles that can accommodate large or small tip angles, enabling improved magnetization profiles and reduced RF power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional small-tip-angle parallel transmission RF pulse designs are used with restrictive phase constraints, then the pulse design is simplified, but the magnitude profiles become un-optimized and cannot accommodate large or arbitrary tip angles
Solution Approach 1:
The patent changes the phase constraint parameter from fixed (restrictive) to variable (phase-relaxed), allowing the phase profile to be optimized during the RF pulse design process. This enables accurate design of RF pulses for large or arbitrary tip angles while maintaining homogeneous magnetization profiles, resolving the contradiction between design simplicity and profile optimization.
Solution Approach 2:
The patent introduces an iterative adjustment process where the RF pulse profile is dynamically optimized based on desired magnetization parameters. The phase-relaxed formulation allows the system to adapt and adjust pulse parameters in real-time during optimization, transforming a static simplified design into a dynamic optimized solution.
2Adaptability or versatility
If conventional small-tip-angle RF pulse designs are used, then the design methodology is limited to small angles, but extending to large tip angles requires completely different design approaches
Solution Approach 1:
The patent creates a universal RF pulse design formulation that can handle both small and large tip angles within the same framework. The phase-relaxed optimal control formulation is not limited to small angles like conventional STA methods, enabling a single unified approach to design RF pulses for arbitrary tip angles, thereby enhancing adaptability without requiring separate design methodologies.
3Manufacturing precision
If iterative adjustment of RF pulse profiles is performed using phase-relaxed optimal control, then magnetization profile homogeneity is improved, but computational time and process complexity increase
Solution Approach 1:
The patent implements a feedback mechanism where the RF pulse profile is iteratively adjusted based on the resulting magnetization parameters. The phase-relaxed optimal control formulation continuously monitors and compares actual magnetization profiles with desired profiles, making real-time adjustments to optimize homogeneity. This feedback loop ensures high precision in magnetization profile control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in more homogeneous magnetization profiles and reduced RF power usage, capable of designing RF pulses for both single-channel and multi-channel systems, including those with arbitrary tip angles, enhancing MRI image quality and efficiency.
Implementation Method 1
Radio frequency (RF) coils are used to create pulses of RF energy at or near the resonance frequency of the hydrogen nuclei. These coils are used to add energy to the nuclear spin system in a controlled fashion.
Implementation Method 2
A MRI system also comprises components called gradient coils that produce smaller amplitude, spatially varying magnetic fields when current is applied to them. Typically, gradient coils are designed to produce a magnetic field component that is aligned along the z axis and that varies linearly in amplitude with position along one of the x, y or z axes.
Implementation Method 3
MRI uses a powerful magnet to create a strong, uniform, static magnetic field (i.e., the 'main magnetic field'). When a human body, or part of a human body, is placed in the main magnetic field, the nuclear spins that are associated with the hydrogen nuclei in tissue water become polarized.
Data Source
AI summary
Techniques for designing RF pulses may be configured to produce improved magnitude profiles of the resulting magnetization by relaxing the phase constraint and optimizing the phase profiles. In one embodiment, a spinor-based, optimal control, optimal phase technique may be used to design arbitrary-tip-angle (e.g., large and small tip angle) RF pulses (both parallel transmission and single channel). In another embodiment, small tip angle RF pulses (both parallel transmission and single channel) may be designed using a small-tip-angle (STA) pulse design without phase constraint that is formulated as a parameter optimization problem.