MRI Gradient Coils Using Bipolar Pulses to Reduce Neurological Stimulation
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Solution Overview
Problem
Magnetic field gradients used in MRI procedures cause undesirable neurological stimulation due to their effects on tissue, limiting the duration and strength of gradients to avoid bio-effects, which in turn increases scan time and reduces spatial resolution.
Innovation Solution
The use of solid-state switches and pulse-forming lines to generate magnetic field gradients with higher slew rates and magnitudes, below the threshold for neurological stimulation, allowing for shorter pulse durations and increased gradient strengths without triggering bio-effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetic field gradient strength and slew rate are increased to improve spatial resolution and reduce scan time, then MRI diagnostic capability is improved, but neurological stimulation and bio-effects are triggered
Solution Approach 1:
The patent applies periodic bipolar magnetic gradient pulses with alternating positive and negative lobes. The net area under the curve is zero, creating a periodic action that averages to no net stimulation while maintaining high peak gradients for improved spatial resolution. This resolves the contradiction by using time-varying periodic action rather than continuous or unipolar gradients.
Solution Approach 2:
The patent changes multiple parameters simultaneously: gradient magnitude (high peak values), duration (short pulse widths), shape (bipolar configuration), and timing (interleaved application). By optimizing these parameters, the system achieves high spatial resolution through strong gradients while keeping the net stimulated charge below neurological thresholds through the bipolar zero-area design.
2Object-affected harmful factors
If magnetic field gradient duration is extended to avoid neurological stimulation, then bio-effects are reduced, but scan time increases
Solution Approach 1:
Instead of using long-duration unipolar pulses, the patent employs short-duration bipolar pulses with periodic alternation. The rapid switching between positive and negative lobes creates a periodic pattern that cancels net stimulation while maintaining effective gradient strength throughout the scan, thus reducing both scan time and bio-effects.
Solution Approach 2:
The patent rushes through the gradient application by using very short pulse durations with high slew rates. The bipolar structure allows the system to quickly switch polarity, effectively 'skipping' over the dangerous intermediate states that would cause prolonged neurological stimulation, thereby achieving safe imaging with reduced total exposure time.
3Measurement precision
If magnetic field gradient magnitude is increased to improve image quality, then spatial resolution is enhanced, but neurological tissue stimulation is triggered
Solution Approach 1:
The patent uses high-magnitude bipolar gradients where the positive and negative lobes have equal area. The periodic alternation at high peak magnitudes provides excellent spatial resolution encoding, while the zero-net-area property ensures that despite high instantaneous magnitudes, the integrated neurological stimulation remains below threshold.
Solution Approach 2:
The patent converts the potentially harmful high gradient magnitudes into a beneficial tool by using them in a bipolar configuration. The high peaks provide superior spatial resolution, while the alternating polarity transforms what would be harmful continuous stimulation into a beneficial zero-net-effect pattern that actually suppresses neurological activation through cancellation.
4Productivity
If gradient slew rate is increased to reduce scan time, then productivity is improved, but the threshold for neurological stimulation is exceeded
Solution Approach 1:
The patent employs rapid periodic switching between positive and negative gradient polarities. The high slew rates enable quick transitions between lobes, achieving fast scan times. The periodic bipolar pattern ensures that despite rapid changes, the net stimulated charge integrates to zero or near-zero values, keeping neurological stimulation below thresholds while maximizing productivity.
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 bio-effects from magnetic field gradients, enabling faster MRI scans and higher spatial resolution by applying gradients within a time frame that avoids neurological responses, while maintaining safety and improving diagnostic capabilities.
Implementation Method 1
Magnetic field gradients used in MRI procedures cause undesirable neurological stimulation due to their effects on tissue
Implementation Method 2
changes in magnetic fields can cause electrical field generation and consequent neurological stimulation
Data Source
AI summary
A magnetic field generator includes a power source and a segmented or un-segmented coil connected to the power source to generate a time-varying magnetic field. Energy is applied to the coil so that the coil generates a time-varying magnetic field gradient with a magnitude of at least 1 milliTesla per meter and a rise-time of less than 1000 microseconds. The coil may be comprised of overlapping, non-overlapping or partially overlapping coil segments that may individually energized to further improve the operating characteristics of the coil to further decrease bio-effects in magnetic resonance imaging through the use of reduced pulse lengths and multi-phasic magnetic gradient pulses.