Quadratic Phase RF Pulse for MRI Slice Encoding
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Solution Overview
Problem
Magnetic resonance imaging (MRI) faces challenges in achieving high spatial resolution due to low signal-to-noise ratio (SNR) at higher frequencies, particularly in slice-encoding directions, which are prone to motion-induced inconsistencies and data variability, hindering efficient acquisition and reconstruction of high-resolution images.
Innovation Solution
The implementation of a frequency-swept RF excitation with a quadratic phase profile, known as SQUASHER, which spreads signal content along the slice-encoding direction, enabling robust acceleration rates and motion correction, and allowing for undersampling in both slice and phase-encoding directions, thereby improving SNR and image resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard 3D encoding is used with segmentation along slow or slowest slice-encoding direction, then complete k-space sampling is achieved, but motion-induced data inconsistencies and field variations increase
Solution Approach 1:
The patent applies quadratic phase modulation to the RF excitation pulse, which transforms the k-space sampling trajectory. This parameter change in the excitation pulse shape redistributes the signal across k-space in a manner that reduces sensitivity to motion-induced phase variations, thereby maintaining data consistency while achieving complete sampling
Solution Approach 2:
The patent combines multiple encoding strategies by integrating quadratic phase modulation with conventional gradient encoding schemes. This composite approach merges the advantages of both methods: the motion robustness of quadratic phase encoding with the sampling efficiency of gradient-based k-space traversal
2Measurement precision
If higher spatial resolution imaging is pursued in MRI, then image quality improves, but signal-to-noise ratio decreases
Solution Approach 1:
The patent modifies the RF excitation pulse parameters by applying quadratic phase modulation, which changes the k-space weighting function. This parameter change allows for more efficient signal distribution across k-space, improving the SNR at high spatial frequencies and enabling higher resolution imaging with adequate signal quality
3Reliability
If segmented 3D k-space acquisition is used, then higher SNR is achieved, but acquisition time increases
Solution Approach 1:
The patent applies quadratic phase modulation to the excitation pulse as a preliminary action that pre-conditions the signal distribution in k-space. This preliminary phase encoding reduces the need for extensive segmented acquisitions, allowing for faster single-shot or few-shot imaging while maintaining high SNR through optimized signal distribution
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 enhances SNR and facilitates faster acquisition of high-resolution images by correcting for motion and undersampling, achieving sub-millimeter isotropic resolution and reducing artifacts, suitable for applications like fMRI and dMRI.
Implementation Method 1
A radio frequency (RF) excitation waveform is provided to the MRI system. The RF excitation waveform defines a frequency-swept RF excitation with a quadratic phase profile (e.g., a quadratic phase profile along a slice-encoding direction).
Data Source
AI summary
Described here are systems and methods for volumetric excitation in magnetic resonance imaging (“MRI”) using frequency modulated radio frequency (“RF”) pulses. In general, quadratic phase modulation along the slice encoding direction is implemented for additional spatiotemporal encoding, which better distributes signal content in the slice direction and enables higher acceleration rates that are robust to slice-undersampling.