Magnetic Field Gradient Pulse Shaping for MRI Bio-Effect Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Magnetic field gradients used in MRI procedures can cause undesirable bio-effects on neurological tissue due to electrical pulses induced in nerves, limiting the duration and strength of gradient pulses to avoid neuronal stimulation, which in turn increases scan time and reduces spatial resolution.
Innovation Solution
The use of high-power solid-state switches and pulse-forming lines to generate magnetic field gradients with shorter rise and fall times, allowing for higher gradient strengths without triggering bio-effects by capitalizing on the physiological loophole of bi-phasic pulses being too fast for nerve polarization change, and incorporating downstream modifications such as eddy current shielding and larger cryostat bores.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If magnetic field gradient strength is increased to improve spatial resolution and reduce scan time, then MRI efficiency and diagnostic quality improve, but bio-effects on neurological tissue increase due to induced electrical pulses
Solution Approach 1:
The patent applies bi-phasic gradient pulses that switch polarity mid-cycle, creating periodic action with alternating positive and negative lobes. This periodic reversal prevents sustained nerve depolarization while maintaining high peak gradient strengths, thereby reducing bio-effects during rapid imaging sequences
Solution Approach 2:
The patent changes the temporal parameters of gradient pulses by using very short duration pulses (sub-millisecond) with high peak amplitudes. This parameter change exploits the physiological loophole where nerves cannot polarize fast enough to respond to such rapid transitions, allowing high gradient strengths without proportional increase in bio-effects
2Object-affected harmful factors
If gradient pulse duration is extended to allow nerve polarization response, then bio-effects are reduced, but spatial resolution and scan time efficiency deteriorate
Solution Approach 1:
By implementing bi-phasic pulses with periodic polarity reversal, the system maintains high gradient amplitudes for sufficient spatial encoding while the alternating nature prevents cumulative nerve stimulation, achieving both high resolution and reduced bio-effects
Solution Approach 2:
The patent rushes through the gradient application in very short time frames (sub-millisecond) with high amplitude, skipping the time window where nerve polarization could occur. This allows high spatial resolution encoding before biological response can initiate
3Speed
If rise time of magnetic field gradient is decreased to improve temporal resolution, then scan efficiency improves, but induced electrical field strength increases causing more bio-effects
Solution Approach 1:
The bi-phasic gradient waveform introduces periodic action with rapid rise and fall times for each lobe, but the alternating polarity means that high slew rates are applied in both positive and negative directions, preventing sustained electrical field induction in neural tissue while maintaining high temporal resolution
Solution Approach 2:
The patent converts the potentially harmful high induced electrical fields from rapid slew rates into a beneficial effect by using bi-phasic waveforms. The alternating polarity causes equal and opposite electrical field inductions that cancel out in neural tissue, transforming what would be harmful rapid changes into a safe imaging approach
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 enables the application of magnetic field gradients up to five times stronger than traditional methods, reducing scan times and improving spatial resolution while minimizing bio-effects, thus enhancing MRI efficiency and diagnostic quality.
Implementation Method 1
changes in magnetic field gradients result in the generation of electrical fields
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A magnetic field generator includes a power source and a 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. One or more of a capacitor, a multi-stage high-voltage switch, and/or a pulse-forming network may assist with the generation of the magnetic field gradient.