MRI B1 Field Limiting via Position-Dependent Conversion Coefficient
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Solution Overview
Problem
Current MR scanners limit the B1 field strength to prevent overheating, resulting in wasted performance due to a one-size-fits-all approach that does not account for varying patient sizes, leading to inefficient RF alternating magnetic field usage and potential safety issues.
Innovation Solution
A method and apparatus that measure the perpendicular distance between the local coil and the detection hole center to determine a conversion coefficient, allowing for the computation of a maximum permissible B1 field strength, ensuring patient safety and optimizing RF alternating magnetic field performance by adjusting field strength based on the specific scanning conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the B1 field strength is limited to a very low value to ensure patient safety and prevent overheating, then the surface temperature of the local coil remains under 41° C., but the performance of the B1 field is wasted due to insufficient field strength for optimal imaging
Solution Approach 1:
The patent applies local quality by differentiating the B1 field limitation based on the local position of the patient's body within the detection hole. Instead of a uniform low field strength limit, the system calculates a position-specific conversion coefficient (α) based on the perpendicular distance from the detection hole center, allowing each local region to have an optimized field strength limit that balances safety and performance.
Solution Approach 2:
The patent implements dynamics by making the B1 field strength limit adaptive rather than static. The conversion coefficient α is dynamically determined based on the measured perpendicular distance S, allowing the field strength limit to adjust in real-time according to the patient's actual position, thereby optimizing both safety and imaging performance for each scanning scenario.
2Reliability
If a uniform B1 field strength limit is applied to all patients regardless of their size and position, then patient safety is ensured, but the B1 field performance is wasted due to the one-size-fits-all approach
Solution Approach 1:
The patent applies parameter changes by modifying the B1 field strength parameter based on the perpendicular distance S from the detection hole center. The conversion coefficient α is calculated as a function of S (α=10S/20), which changes the effective field strength parameter according to position, allowing the system to adapt to different patient sizes and positions while maintaining safety and optimizing performance.
3Reliability
If the B1 field strength is set too low to comply with the new MS-14 test standard for old RF coils, then the surface temperature requirement is met, but the imaging quality and performance are compromised
Solution Approach 1:
The patent applies segmentation by dividing the detection hole space into different regions based on the perpendicular distance from the center. This segmentation allows the system to apply different B1 field strength limits to different spatial zones, ensuring compliance with safety standards in critical areas while maintaining higher performance in regions where patients are less likely to be positioned.
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 wastage of B1 field performance while maintaining patient safety and improving MR imaging quality by dynamically adjusting the B1 field strength according to the patient's size and scanning position.
Implementation Method 1
the RF alternating magnetic field generated by a transmit coil, i.e. the B1 field
Implementation Method 2
the surface temperature of a local coil placed on the part of the body being scanned must remain under 41° C. at the RF power
Data Source
AI summary
A method and apparatus for limiting an RF alternating magnetic field in MRI. The method includes: measuring a perpendicular distance between a local coil placed on a scanned part of a patient and the center of a detection hole of a magnetic resonance (MR) scanner; based on the perpendicular distance, determining a deviation between the B1 field strength at the position of the local coil during an MR scan and the B1 field strength at the center of the detection hole; based on the deviation, computing a conversion coefficient for conversion between the B1 field strength at the position of the local coil and the B1 field strength at the center of the detection hole; based on the B1 field strength required when the surface temperature of the local coil is equal to a safe temperature upper limit and the conversion coefficient, computing a maximum permissible field strength of the B1 field at the center of the detection hole. The B1 field may be limited to a smaller but still effective field strength range, reducing wastage of B1 field performance while ensuring patient safety and MR imaging quality.