Bi-phasic MRI Gradient Coils for Neuronal Stimulation Reduction
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Solution Overview
Problem
Magnetic field gradients used in MRI procedures cause undesirable bio-effects on neurological tissue due to neuronal stimulation, limiting the duration and intensity of magnetic field gradients that can be applied without adverse effects.
Innovation Solution
The use of solid-state switches and pulse-forming lines to generate magnetic field gradients with higher intensity and shorter durations, capitalizing on the physiological loophole of bi-phasic pulses that are too fast for nerve polarization, and employing segmented coils to minimize eddy currents and mechanical stabilization requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If magnetic field gradient intensity is increased to improve spatial resolution and reduce scan time, then MRI efficiency and diagnostic capability are improved, but neuronal stimulation and bio-effects on neurological tissue occur
Solution Approach 1:
The patent applies periodic bi-phasic magnetic field gradients with alternating polarity. The gradient waveform switches between positive and negative phases, creating periodic action that prevents sustained neuronal depolarization. This periodic reversal allows higher intensity gradients to be applied without causing continuous neuronal stimulation, thus improving scan efficiency while reducing bio-effects.
Solution Approach 2:
The patent changes multiple parameters of the magnetic field gradient including intensity (up to 5 times stronger than traditional), duration (shorter pulses), and waveform shape (bi-phasic). By optimizing these parameters together, the system achieves higher spatial resolution and faster scanning while keeping the gradient intensity below the threshold for sustained neuronal stimulation.
2Measurement precision
If magnetic field gradient intensity is increased to improve spatial resolution, then image quality is improved, but bio-effects on neurological tissue increase
Solution Approach 1:
The bi-phasic gradient waveform with periodic polarity reversal prevents sustained neuronal depolarization while maintaining high gradient intensity. This allows stronger gradients (5 times stronger than traditional) to be used for improved spatial resolution without causing excessive bio-effects, as the alternating phases prevent cumulative neuronal stimulation.
Solution Approach 2:
The patent optimizes the combination of gradient intensity, pulse duration, and waveform shape. By using shorter, more intense bi-phasic pulses, the system achieves higher spatial resolution through stronger gradients while the shortened duration and alternating polarity reduce the total bio-effective exposure to neurological tissue.
3Reliability
If traditional magnetic field gradient durations are used to avoid neuronal stimulation, then safety is maintained, but scan time increases
Solution Approach 1:
The bi-phasic gradient applies periodic reversal of polarity during the pulse duration. This periodic action prevents sustained neuronal depolarization even at higher intensities and longer durations than traditional single-phase gradients. The safety threshold is maintained through the alternating phases while allowing longer total pulse durations for faster imaging sequences.
Solution Approach 2:
The patent enables continuous application of high-intensity gradients throughout the imaging sequence without interruption for safety reasons. The bi-phasic waveform allows the gradient to be continuously applied at higher intensities than traditional methods, maintaining safety through periodic polarity reversal while reducing total scan time through more efficient k-space sampling.
4Productivity
If stronger magnetic field gradients are applied to reduce scan time, then productivity is improved, but the duration of gradient application must be extended which increases bio-effects
Solution Approach 1:
The bi-phasic gradient waveform applies periodic polarity reversal during the gradient pulse. This periodic action allows the gradient to be applied at higher intensities for longer durations without causing sustained neuronal depolarization. The alternating phases create a net-zero effect on neuronal membrane potential over each cycle, enabling extended gradient application for faster imaging while maintaining safety.
Solution Approach 2:
The patent changes the waveform shape from traditional single-phase to bi-phasic, allowing simultaneous increase in gradient intensity and duration. The bi-phasic shape with area-balanced positive and negative lobes enables longer pulse durations for faster scanning while the alternating polarity prevents cumulative bio-effects, resolving the trade-off between productivity and gradient duration.
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 allows for the application of magnetic field gradients up to five times stronger than traditional methods while avoiding bio-effects, reducing scan time and improving spatial resolution without triggering neuronal stimulation, thus enhancing MRI efficiency and diagnostic capabilities.
Implementation Method 1
solid-state switches and pulse-forming lines to generate magnetic field gradients
Implementation Method 2
changes in magnetic field gradients depolarize nerves, once a threshold is reached
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 10 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.