Patient-Specific Multi-Band Spokes RF Pulses for B1+ Homogeneity in MRI
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Solution Overview
Problem
Existing methods for multi-band RF excitation in ultra-high field magnetic resonance imaging fail to account for patient-specific B1+ inhomogeneity, particularly when using spokes RF pulses for simultaneous multi-slice excitation, leading to sub-optimal excitation homogeneity.
Innovation Solution
A method for subject-specific optimization of multi-band RF pulses using an iterative inverse Fourier transform to determine optimal spokes locations in k-space, taking into account patient-specific B0 and B1+ field maps, ensuring each slice's magnetization aligns with a target distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional single-band excitation with inverse Fourier transform method is used, then computational simplicity and real-time design capability are improved, but the method breaks down when considering simultaneous multi-slice excitation with different optimal spokes locations
Solution Approach 1:
The patent segments the optimization problem by processing each slice independently through the inverse Fourier transform method, then combines the results. Each slice is optimized separately for its optimal spokes locations, and the individual optimizations are aggregated to form the final multi-slice pulse sequence, resolving the contradiction between computational simplicity and multi-slice adaptability
Solution Approach 2:
The patent extends the traditional single-band inverse Fourier transform method to a multi-dimensional framework by adding the slice dimension. The optimization is performed across multiple slices simultaneously while maintaining the computational efficiency of the inverse Fourier transform, thereby achieving both simplicity and versatility
2Manufacturing precision
If static RF shims are optimized for multi-band imaging, then excitation homogeneity is improved, but the method does not use spokes RF pulses and cannot achieve optimal in-plane gradient positioning
Solution Approach 1:
The patent merges two previously separate approaches: the static RF shim optimization for homogeneity and the spokes RF pulse design with in-plane gradients. By combining these elements, the patent achieves both excitation homogeneity and optimal gradient positioning in a single integrated pulse sequence
Solution Approach 2:
The patent dynamically adjusts multiple parameters including RF channel weights, spoke positions, and gradient amplitudes to optimize the pulse sequence. This multi-parameter optimization enables simultaneous achievement of homogeneity and complexity reduction
3Productivity
If multiple slices are excited simultaneously with different optimal spokes locations, then acquisition time is reduced, but the optimization becomes computationally intensive and complex
Solution Approach 1:
The patent segments the optimization computation across multiple slices, processing each slice independently through the inverse Fourier transform method. This segmentation allows parallel computation and maintains efficiency while handling multiple slices simultaneously
Solution Approach 2:
The patent uses the inverse Fourier transform method, which is a well-established and computationally efficient algorithm, to generate the pulse sequence. By copying and adapting this proven method to multi-slice excitation, the patent achieves fast computation without excessive complexity
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
Achieves improved B1+ field homogeneity across multiple slices, enhancing the quality of magnetic resonance imaging by optimizing RF pulses for each imaging session, reducing errors, and maintaining efficient acquisition times.
Implementation Method 1
RF pulses that are necessary to excite the spins within the field-of-view
Implementation Method 2
radiofrequency (RF) pulses with different shapes, amplitudes, and phases
Implementation Method 3
gradient blips determine the transmit k-space locations of the spokes
Data Source
AI summary
A method for optimization of an RF pulse that is multi-band. The RF pulse is a spokes RF pulse including a train of sub-pulses. The method includes using a starting k-space position as a current k-space position, and for each of slices to be excited by the RF pulse, performing: calculating a sub-pulse based on the current k-space position and calculating an expected magnetization after that sub-pulse; calculating an inverse Fourier transform of a difference between an expected magnetization and a target magnetization; and determining an optimal k-space position for a next spoke for this slice to be at a position where an absolute value of the inverse Fourier transform has a maximum. A next k-space position is determined for all slices together based on the optimal k-space positions determined for each slice individually. A multi-band RF pulse is determined based on the determined k-space positions.