Universal Pulse Sequence Design for Parallel-Transmission MRI
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Solution Overview
Problem
High-field magnetic resonance imaging (MRI) systems face challenges with B1 artifact issues, particularly at 3 T and above, leading to inhomogeneous nuclear magnetization and reduced diagnostic accuracy due to the limitations of existing active RF shimming techniques, which require time-consuming calibration processes and do not always ensure homogeneous excitation across all subjects.
Innovation Solution
A method that estimates a linear adjustment transformation to convert subject-specific RF field maps into standardized maps, allowing for the design of universal pulse sequences that can be customized for individual subjects using a simpler calibration process, thereby reducing inter-subject variability in the TX field distribution and improving homogeneity without session-specific pulse engineering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If subject-specific pulse sequences are designed using traditional calibration methods, then excitation homogeneity is improved, but calibration time and system complexity increase significantly
Solution Approach 1:
The patent designs a universal pulse sequence that can be applied across multiple subjects without requiring subject-specific calibration. The pulse sequence incorporates a set of RF waveforms and gradient waveforms that work effectively for a broad population, eliminating the need for individual calibration while maintaining acceptable excitation homogeneity across different subjects
Solution Approach 2:
The patent modifies traditional calibration-based pulse design by changing the approach to parameter selection. Instead of calculating subject-specific parameters through time-consuming B1+ mapping and optimization, the method uses a predefined set of pulse parameters that have been optimized for universal applicability, significantly reducing calibration time while maintaining precision
2Manufacturing precision
If traditional B1 artifact correction methods are used, then excitation uniformity is improved, but device complexity and calibration requirements increase
Solution Approach 1:
The patent extracts the essential function of B1 correction from the complex calibration process. By identifying and isolating the key factors that cause B1 inhomogeneity, the method uses a simplified pulse sequence design that directly addresses these factors without requiring comprehensive calibration measurements and optimization procedures
Solution Approach 2:
The patent employs a disposable universal pulse sequence that does not require expensive or complex calibration procedures. The pulse sequence is pre-optimized and can be applied directly without needing subject-specific calibration equipment or time-consuming measurement processes, reducing both device complexity and operational burden
3Manufacturing precision
If dynamic RF shimming is implemented, then excitation homogeneity is improved, but computational complexity and calibration time increase
Solution Approach 1:
The patent applies partial action by using a limited set of RF waveforms and gradient waveforms that are sufficient to achieve acceptable excitation homogeneity without requiring the full complexity of dynamic RF shimming. The method selects a subset of pulse parameters that provide adequate correction for B1 inhomogeneity while avoiding the computational burden of complete dynamic optimization
Solution Approach 2:
The patent creates a universal pulse sequence that performs RF shimming functionality across multiple subjects without requiring subject-specific computational optimization. The pulse sequence is designed to be applicable to a broad population, eliminating the need for individualized computational calibration while maintaining excitation homogeneity
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 provides better fidelity to target excitation patterns with reduced calibration requirements, achieving improved uniformity in MRI imaging across subjects, comparable to or exceeding the performance of subject-tailored pulses while requiring less extensive calibration, and efficiently mapping the TX field distribution in a virtual space.
Implementation Method 1
A pulse sequence comprises one or more radio-frequency (RF) waveforms, or pulses, and at least one magnetic field gradient waveform, allowing manipulating the nuclear magnetization of a sample immersed in a static magnetic field, resulting from the orientation of nuclear spins
Data Source
AI summary
A method of designing a pulse sequence for parallel-transmission MRI includes a) for each one of a plurality of subjects, estimating a linear adjustment transformation (L), converting amplitude maps of RF fields generated by respective transmit channels of a MRI apparatus into respective standardized maps; and b) determining RF waveforms (P) minimizing a discrepancy between subject-specific distributions of flip-angles of nuclear spin and a target distribution, averaged over said subjects, the subject-specific distributions corresponding to the flip-angle distributions achieved by applying a superposition of RF fields, each having a temporal profile described by one of said RF waveforms and a spatial amplitude distribution described by a respective standardized map determined for the subject. A method and an apparatus for performing parallel-transmission MRI using such a pulse sequence are provided.