MRI Gradient Pulse Stimulation Threshold Calculation
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Solution Overview
Problem
Current methods for controlling patient stimulation in MRI, such as the SAFE-model and traditional effective stimulus duration calculations, either fail to reliably prevent unwanted stimulations or lead to unnecessarily reduced imaging performance by setting overly conservative limits.
Innovation Solution
A method that calculates two effective stimulus durations for MRI sequences, one based on standard IEC 60601-2-33 and another considering the history of the gradient field, to determine a safe threshold for magnetic gradient changes, allowing for flexible and safe imaging while optimizing performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the SAFE-model is used to monitor MRI sequences for PNS, then patient safety is ensured even for worst-case sequences, but the limits are unnecessarily low and imaging performance is reduced
Solution Approach 1:
The patent applies local quality by evaluating gradient pulses individually based on their specific characteristics (monotonic flanks, effective stimulus duration) rather than applying a uniform conservative limit to all sequences. This allows each gradient pulse to be assessed according to its actual stimulation risk, enabling safer sequences to proceed at full performance while only restricting potentially harmful ones.
Solution Approach 2:
The patent introduces dynamics by calculating effective stimulus duration dynamically for each gradient pulse based on its actual waveform and temporal characteristics, rather than using static conservative limits. The method adapts the safety assessment to the specific pulse sequence being executed, allowing optimal performance when safety conditions are met while maintaining protection when risks are present.
2Device complexity
If traditional effective stimulus duration calculation is used for each gradient pulse, then computational simplicity is maintained, but patient stimulation cannot be reliably prevented in all cases
Solution Approach 1:
The patent segments the gradient pulse evaluation into distinct components: identifying monotonic flanks, calculating effective stimulus duration for each flank individually, and comparing against safety thresholds. This segmentation allows the system to focus computational resources on the critical aspects of stimulation risk while maintaining overall simplicity and reliability.
Solution Approach 2:
The patent performs preliminary action by calculating the effective stimulus duration for each gradient pulse in advance, before the actual MRI sequence is executed. This allows safety verification to be completed beforehand, ensuring that only sequences meeting safety criteria are run, thereby reliably preventing stimulation while maintaining simple real-time operation.
3Reliability
If conservative limits are set to prevent cardiac stimulation, then patient safety is improved, but the safe range of MRI sequences is not fully utilized
Solution Approach 1:
The patent applies parameter changes by using multiple effective stimulus duration thresholds (first threshold for PNS, second threshold for cardiac stimulation) instead of a single conservative limit. This allows the system to accommodate a broader range of sequence parameters by adjusting the applicable threshold based on the specific stimulation risk being evaluated, thereby improving both safety and sequence flexibility.
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 provides reliable monitoring and control of patient stimulation effects, ensuring safety while maintaining or improving imaging performance compared to existing techniques, and can be implemented with limited computational resources.
Implementation Method 1
the rapidly changing magnetic fields may lead to relatively strong electrical fields that in turn may potentially lead to unwanted peripheral nerve stimulation (PNS) and/or cardiac stimulations in patients
Data Source
AI summary
Methods and systems for controlling patient stimulating effects in MR imaging. The methods and systems include calculating a first effective stimulus duration independently for each pulse flank of an MRI sequence individually and calculating a second effective stimulus duration for which a respective history of a changing gradient field during the sequence is taken into account. Dependent on an evaluation of both the first and second effective stimulus durations a threshold value for an allowable rate of change in the magnetic gradient field is then calculated. The respective MRI sequence is then evaluated against the calculated threshold value to determine whether or not the respective MRI sequence is safe to apply.