Multi-Spoke MRI Excitation Sequences for Uniform Slice Flip Angles
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Solution Overview
Problem
Existing MRI techniques face challenges in achieving homogeneous spin-excitation across multiple slices due to computational complexity and discontinuities in contrast between slices, especially at high magnetic fields, which hinder image quality and recombination of images in non-aligned planes.
Innovation Solution
A method for designing multi-spoke spin-excitation sequences using a global parameterization of RF and gradient signals, optimized for each slice's position and orientation, allowing for simple and instantaneous computation and reducing discontinuities by employing truncated series of functions to define RF and gradient pulse parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If independent optimization is performed for each slice to achieve homogeneous spin-excitation, then excitation homogeneity in each slice is improved, but computational complexity increases significantly
Solution Approach 1:
The patent creates a single global parameterization that serves all slices simultaneously, rather than optimizing each slice independently. This universal parameterization defines RF and gradient signals that work across the entire multi-slice volume, reducing computational burden while maintaining excitation homogeneity through a unified optimization framework.
Solution Approach 2:
The patent merges the optimization of multiple slices into a single unified parameterization. By combining the RF and gradient signal definitions into one global set of parameters that applies to all slices, the computational complexity is reduced from N separate optimizations to one integrated optimization problem.
2Manufacturing precision
If independent optimization is performed for each slice, then spin-excitation homogeneity in each slice is improved, but discontinuities in contrast between slices occur
Solution Approach 1:
The global parameterization ensures that the same set of RF and gradient signal parameters is used across all slices, creating a unified excitation profile. This universality eliminates the discontinuities that arise when each slice is optimized independently, as the parameters are coordinated across the entire multi-slice volume to maintain contrast continuity.
3Productivity
If global parameterization is used for multi-slice sequences, then computational burden is reduced, but achieving uniform flip angle across all slices becomes more challenging
Solution Approach 1:
The patent incorporates feedback mechanisms in the global optimization process, where the parameterization is iteratively refined based on the actual excitation profiles across all slices. This feedback loop allows the system to achieve uniform flip angles across slices while maintaining the computational efficiency of a unified parameterization approach.
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
The method ensures uniform flip angle excitation across slices, minimizing mean deviation and reducing computational burden, thereby improving image quality and enabling seamless image reconstruction across various planes.
Implementation Method 1
radiofrequency pulses at a Larmor frequency of nuclear spins alternated with magnetic gradient pulses
Implementation Method 2
magnetic gradient pulses, with the value of each parameter of each of said sets being expressed by a truncated series of functions of a position coordinate
Data Source
AI summary
A method for determining a global and regular parameterization for a family of spin-excitation pulse sequences in magnetic resonance imaging, with each pulse sequence of the family being a multi-spoke type sequence suitable for selectively exciting nuclear spins in a slice of a volume of interest of a body immersed in a static magnetic field and comprising radiofrequency pulses at a Larmor frequency of the nuclear spins alternated with magnetic gradient pulses. The global parameterization minimizes a function representing a mean deviation from a setpoint of the excitation of the nuclear spins, with the mean being computed for the volume of interest and for all the possible orientations and positions of the slices. It allows a selective excitation sequence to be simply designed for a slice with a random orientation and position.