Multiband RF Pulse MRI Phase Encoding Near Metal
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Solution Overview
Problem
Conventional MRI methods face challenges in imaging near metallic implants due to severe off-resonance-induced signal loss and image distortion, as they require frequency-encoding gradients that are limited by the strong magnetic field inhomogeneities caused by metal objects, leading to prolonged scan times and suboptimal diagnostic quality.
Innovation Solution
The implementation of multiband radio frequency (RF) excitation to simultaneously excite spins associated with multiple resonance frequency offsets, combined with phase-encoding gradients in three dimensions, eliminating the need for frequency-encoding gradients and reducing scan time by allowing for spectrally-resolved, fully phase-encoded three-dimensional MRI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency-encoding gradients are used for spatial localization, then spatial encoding is achieved, but signal loss and pile-up occur when local B0 gradients near metal exceed the readout gradient
Solution Approach 1:
The patent removes the frequency-encoding gradient from the pulse sequence, eliminating the source of spatial encoding errors near metal. Instead of using frequency encoding, the invention relies on phase encoding in all three dimensions, thereby extracting the problematic frequency-encoding component that causes signal pile-up and loss in regions with strong local B0 gradients.
Solution Approach 2:
Conventional MRI uses phase encoding in two dimensions and frequency encoding in one dimension. This patent inverts the approach by using phase encoding in all three dimensions and eliminating frequency encoding entirely. This inversion allows the method to avoid the fundamental limitation of frequency encoding when local gradients exceed readout gradients.
2Adaptability or versatility
If multiple three-dimensional acquisitions at distinct RF offsets are performed to excite the full spectrum of off-resonance, then spectral coverage is improved, but scan time increases to a level that may be clinically prohibitive
Solution Approach 1:
The patent combines multiple RF offset acquisitions into a single integrated pulse sequence. By using phase encoding in all three dimensions and implementing a unified acquisition scheme that simultaneously handles multiple frequency offsets, the invention merges what would otherwise require multiple separate scans into one clinically feasible procedure, thereby maintaining spectral coverage while dramatically reducing scan time.
3Productivity
If conventional spatial-encoding mechanisms are used, then standard MRI imaging is achieved, but severe off-resonance causes signal loss and image distortion
Solution Approach 1:
The patent fundamentally changes the encoding parameters by eliminating the frequency-encoding gradient and using phase encoding in all three dimensions. This parameter change transforms the imaging approach from one that is sensitive to local B0 gradients to one that is robust against such gradients, thereby maintaining image quality near metal implants while preserving standard MRI imaging capability.
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 significantly reduces scan time, enables distortion-free imaging near metal implants, and improves visualization of tissues in proximity to metallic objects, facilitating clinical evaluations by accelerating data acquisition while maintaining high signal-to-noise ratio and spatial resolution.
Implementation Method 1
produce a multiband RF pulse that excites spins associated with each of a plurality of different resonance frequency offsets
Implementation Method 2
establish a first phase-encoding gradient along a first direction, a second phase-encoding gradient along a second direction that is orthogonal to the first direction, and a third phase-encoding gradient along a third direction that is orthogonal to the first direction and the second direction
Implementation Method 3
Data are acquired at a point in k-space that is defined by the first, second, and third phase-encoding gradients by sampling a magnetic resonance signal
Data Source
AI summary
Systems and methods for simultaneously acquiring three-dimensional data from multiple different frequency bins with a magnetic resonance imaging (“MRI”) system, and without frequency-encoding gradients, are provided. A multiband radio frequency (“RF”) pulse is used to excite spins associated with multiple different resonance frequency offsets, and a fully phase-encoded acquisition is used to acquire data, which may be spectrally-resolved data, from magnetic resonance signals formed in response to the multiband RF pulse.