Maxwell Compensation for Non-Rectilinear TSE MRI Imaging
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Solution Overview
Problem
Magnetic resonance imaging (MRI) systems face challenges in correcting image artifacts caused by Maxwell terms, particularly at lower magnetic field strengths, due to concomitant gradient effects which result in signal dropouts and image blurring in turbo spin-echo (TSE) imaging using non-rectilinear encoding gradient waveforms.
Innovation Solution
The method involves modifying the original encoding gradient waveform by adjusting portions or introducing zero zeroth-moment waveform segments at the ends, and generating additional gradient pulses according to the modified waveform to encode NMR spin-echo signals, thereby reducing the impact of Maxwell terms and improving image quality in 2D interleaved-spiral and spiral-ring TSE imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If non-rectilinear encoding gradient waveforms are used in TSE imaging, then signal-to-noise ratio efficiency and image contrast are improved, but Maxwell field induced phase errors cause signal dropouts and image blurring
Solution Approach 1:
The patent applies preliminary anti-action by modifying the gradient waveform beforehand to compensate for Maxwell terms. Specifically, the gradient waveform is adjusted to pre-correct for the concomitant field effects that would otherwise cause phase errors during the imaging process, thereby preventing signal dropouts and image blurring before they occur
Solution Approach 2:
The patent employs parameter changes by modifying the gradient waveform parameters (amplitude, timing, shape) to account for Maxwell terms. The gradient waveform is adjusted in terms of its temporal and spatial characteristics to compensate for the field inhomogeneities, transforming the parameter set to achieve both high SNR and artifact reduction
2Measurement precision
If gradient amplitudes are increased to improve image quality, then signal fidelity is enhanced, but Maxwell terms become larger and cause more severe artifacts at lower field strengths
Solution Approach 1:
The patent applies parameter changes by modifying the gradient waveform parameters to compensate for Maxwell terms. The gradient amplitude, timing, and shape are adjusted to maintain signal fidelity while accounting for the increased Maxwell effects at lower field strengths, thereby reducing artifacts without sacrificing image quality
Solution Approach 2:
The patent introduces an intermediary approach by using modified gradient waveforms that act as a mediator between the desired high signal fidelity and the problematic Maxwell terms. The adjusted waveform serves as an intermediate solution that balances the competing requirements of strong gradients for signal quality and controlled gradients to minimize concomitant field effects
3Object-affected harmful factors
If conventional gradient waveform modification strategies are applied, then some Maxwell effects are addressed, but they are insufficient to adequately mitigate effects in TSE imaging using non-rectilinear encoding gradient waveforms
Solution Approach 1:
The patent employs parameter changes by systematically adjusting gradient waveform parameters (amplitude, timing, shape) to compensate for Maxwell terms in non-rectilinear encoding. This goes beyond conventional strategies by applying comprehensive parameter modifications tailored to spiral and other non-Cartesian trajectories, achieving adequate mitigation of Maxwell effects
Solution Approach 2:
The patent applies segmentation by dividing the gradient waveform into distinct segments (e.g., pre-phasing, readout, rephasing portions) and modifying each segment separately to address Maxwell terms at different stages of the echo train. This segmented approach allows for targeted corrections without requiring complete waveform redesign
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 effectively mitigates image degradation from Maxwell terms and B0-inhomogeneity-induced phase accruals, enhancing MRI image quality at lower magnetic field strengths by compensating for self-squared and quadratic Maxwell gradient terms, leading to improved signal fidelity and reduced artifacts.
Implementation Method 1
generating a radio frequency (RF) excitation pulse to produce transverse magnetization that generates a nuclear magnetic resonance (NMR) signal
Implementation Method 2
a series of RF refocusing pulses to produce a corresponding series of NMR spin-echo signals
Implementation Method 3
magnetic field gradients (e.g., gx, gy, and gz) are employed for spatial encoding
Data Source
AI summary
Methods, computing devices, and MRI systems that reduce artifacts produced by Maxwell gradient terms in TSE imaging using non-rectilinear trajectories are disclosed. With this technology, a RF excitation pulse is generated to produce transverse magnetization that generates a NMR signal and a series of RF refocusing pulses to produce a corresponding series of NMR spin-echo signals. An original encoding gradient waveform comprising a non-rectilinear trajectory is modified by adjusting a portion of the original encoding gradient waveform or introducing a zero zeroth-moment waveform segment at end(s) of the original encoding gradient waveform. During an interval adjacent to each of the series of RF refocusing pulses a first gradient pulse is generated. At least one of the first gradient pulses is generated according to the modified gradient waveform. An image is constructed from generated digitized samples of the NMR spin-echo signals obtained.