Gradient Waveform Correction via Phase Encode Segmentation
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Solution Overview
Problem
Current magnetic resonance imaging (MRI) technologies face challenges in accurately measuring and correcting magnetic field gradient waveforms due to limitations in existing methods, such as T2* decay and gradient dephasing, which affect image quality and spatial resolution.
Innovation Solution
A pure phase encode method using a small water droplet in a micro RF coil excited by broadband RF pulses allows for long-duration gradient waveform measurement without T2* decay limitations, decomposing large gradient areas into smaller ones to avoid dephasing, and using a single solenoid probe for simple and high-sensitivity gradient monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If frequency encode magnetic field monitoring with NMR microprobes is used, then gradient waveform measurement is possible, but T2* decay limits the waveform measurement duration
Solution Approach 1:
The gradient waveform measurement is divided into multiple small gradient areas with short time intervals, where each segment is measured separately. This segmentation allows the total measurement duration to extend beyond the T2* decay limit of individual measurements, as each small segment is acquired within the T2* window while the complete waveform spans a much longer duration.
2Measurement precision
If large gradient areas are measured, then high k-space maxima are achieved, but gradient dephasing limits the measurable gradient area
Solution Approach 1:
The large gradient area is decomposed into multiple small separate gradient areas, each measured individually before significant dephasing occurs. By accumulating measurements from these segmented portions, the method achieves high k-space maxima equivalent to large gradient areas while avoiding the dephasing limitations that would prevent measuring the large area as a single unit.
3Measurement precision
If multiple RF microprobes with susceptibility matching are used, then magnetic field monitoring accuracy is improved, but device complexity increases
Solution Approach 1:
The method extracts and eliminates the requirement for susceptibility matching probe components from the system. By using a simple solenoid probe without complex susceptibility-matched materials, the design removes this source of complexity while maintaining measurement capability through the phase encode detection method.
Solution Approach 2:
The invention replaces complex, expensive susceptibility-matched probe components with a simple, easily fabricated solenoid probe. This simplified probe, while less sophisticated than susceptibility-matched designs, achieves the necessary measurement function through the pure phase encode detection methodology, making the overall system cheaper and easier to construct.
4Ease of operation
If conventional gradient waveform measurement methods are used, then basic gradient monitoring is achieved, but image quality problems persist due to residual eddy currents
Solution Approach 1:
The method measures the actual gradient waveform experienced by the sample using pure phase encode detection, providing feedback information about the true gradient conditions. This measured waveform information can then be used to identify and correct deviations caused by eddy currents and other distortions, enabling compensation that improves image quality while maintaining ease of operation.
Data Source
AI summary
Method for correcting the magnetic field gradient waveform in a magnetic resonance measurement including extracting an impulse response from the measured step response of a magnetic resonance system, determining the slew rate of the system during the step response measurement, modifying the desired output waveform such that the desired output waveform is constrained to within the slew rate and the bandwidth of the system, and determining the required pre-equalized input waveform.