Time-Reversed RF Pulse Design for MRI Spin Accuracy
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Solution Overview
Problem
Existing MRI systems face challenges in accurately generating radio frequency (RF) pulses for large tip angle excitation and spin refocusing, leading to design time inefficiencies and inaccuracies due to reliance on numerical corrections based on linear approximations of Bloch equations.
Innovation Solution
A magnetic resonance imaging apparatus and method that utilize time-reversed and sign-reversed RF and gradient pulses, where the second half of each pulse corrects errors in the first half, ensuring robustness and accuracy by concatenating these pulses for application to RF and gradient coils, respectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If numerical iterative corrections are applied to initial RF pulses based on linear approximation of Bloch equations, then spin accuracy is improved, but design time and computer resources are significantly increased
Solution Approach 1:
The patent applies time-reversed and sign-reversed RF and gradient pulses where the second half corrects errors from the first half. This inversion approach provides accurate spin refocusing without requiring iterative numerical corrections, thereby reducing design time while maintaining spin accuracy.
2Manufacturing precision
If numerical iterative corrections are applied to initial RF pulses, then spin accuracy is improved, but computer resources are significantly increased
Solution Approach 1:
The patent uses time-reversed and sign-reversed pulses to correct spin errors, eliminating the need for complex iterative numerical corrections. This approach maintains high spin accuracy while significantly reducing the computational resources required compared to traditional iterative methods.
3Manufacturing precision
If time-reversed and sign-reversed pulses are used for spin refocusing, then spin accuracy is improved, but pulse design complexity is increased
Solution Approach 1:
The patent implements spin refocusing by applying time-reversed and sign-reversed RF and gradient pulses. While this introduces a specific structural requirement, it eliminates the need for complex iterative optimization algorithms, thereby simplifying the overall design process while achieving high spin refocusing accuracy.
4Loss of time
If conventional RF pulses are used without correction, then design time is reduced, but spin accuracy deteriorates
Solution Approach 1:
The patent applies time-reversed and sign-reversed pulses to correct spin errors from the first half of the pulse sequence. This provides accurate spin excitation and refocusing without requiring time-consuming iterative corrections, achieving both speed and accuracy simultaneously.
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 reduces design time and enhances the accuracy of RF pulses, resulting in high-quality MR images with improved contrast fidelity and uniform intensity by effectively correcting for patient-specific distortions in real-time.
Implementation Method 1
a static magnetic field source for generating a static magnetic field for aligning a spin vector of an object in a direction of the magnetic field
Implementation Method 2
nuclear magnetic moments of a portion of the body or other object to be measured are excited at specific spin precession frequencies, which are proportional to the local magnetic field
Implementation Method 3
a second half of each of the plurality of radio frequency excitation pulses comprises a time-reversed first half of a respective one of the plurality of radio frequency excitation pulses
Data Source
AI summary
A magnetic resonance imaging apparatus having a static magnetic field source, a plurality of radio frequency magnetic field sources and a plurality of gradient magnetic field sources for generating a gradient magnetic field is provided. The static magnetic field source generates a static magnetic field for aligning a spin vector of an object in a direction of the magnetic field and plurality of radio frequency magnetic field sources generate a radio frequency magnetic field for rotating the spin vector by an angle. The apparatus further includes a processor for generating a plurality of radio frequency excitation pulses for the plurality of radio frequency magnetic field sources and a plurality of gradient excitation pulses for the plurality of gradient magnetic field sources. The second half of each of the plurality of radio frequency excitation pulses comprises a time-reversed first half of a respective one of the plurality of radio frequency excitation pulses and the second half of each of the plurality of gradient excitation comprises a time-reversed and sign-reversed first half of a respective one of the plurality of gradient excitation pulses. The average value of each of the plurality of gradient excitation pulses is zero.