Magnetic Resonance Coil Calibration for SAR Estimation
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Solution Overview
Problem
Current methods for estimating the specific absorption rate (SAR) in magnetic resonance devices with parallel transmission systems require complex simulation models, leading to increased computing effort and inaccuracy due to the complexity of modeling electromagnetic field interactions between transmitting coil elements and their load situations.
Innovation Solution
A calibration factor is determined based on measured voltage values at a supply line measuring point, allowing conversion to a total voltage value at the feeding point, which is proportional to the electromagnetic field generated by the transmitting coil elements, thereby simplifying the simulation model input and reducing load dependency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If complex simulation models are used to map electromagnetic field interactions and load situations, then the estimation of specific absorption rate can be performed, but the computing effort increases and accuracy decreases
Solution Approach 1:
The patent extracts the load-dependent relationship from the complex simulation model by introducing a calibration factor that captures the impedance and field generation characteristics separately. This allows the simulation model to focus only on the electromagnetic field interactions while the calibration factor handles the load situation dependencies, thereby reducing model complexity while maintaining accuracy.
Solution Approach 2:
The patent changes the parameter representation by introducing a calibration factor that transforms measured voltage values into total voltage values at the feeding point. This parameter transformation simplifies the input requirements for the simulation model, reducing the need to explicitly model complex load situations and impedance variations.
2Measurement precision
If complex simulation models are used to map electromagnetic field interactions, then SAR estimation can be performed, but the computational effort increases
Solution Approach 1:
The patent extracts the computationally intensive load-dependent calculations from the simulation model by pre-determining calibration factors from measured data. This separation allows the simulation to use simpler models with reduced computational effort while still achieving accurate SAR estimation through the calibration correction.
Solution Approach 2:
The patent performs preliminary measurements and calibration factor determination before the actual SAR estimation process. By pre-characterizing the system response and storing calibration factors, the subsequent SAR calculations require significantly less computational effort while maintaining accuracy.
3Measurement precision
If the relationship between fed voltage and generated electromagnetic field depends on load situation and coupling, then accurate SAR estimation requires complex models, but this increases device complexity
Solution Approach 1:
The patent introduces a calibration factor as an intermediary that mediates between the measured voltage values and the total voltage at the feeding point. This intermediary captures the complex load-dependent relationships without requiring the simulation model to explicitly model these dependencies, thereby reducing model complexity while preserving accuracy.
Solution Approach 2:
The patent uses measured voltage values from the actual system as feedback to determine calibration factors that accurately represent the load situation and coupling effects. This feedback mechanism allows the system to adapt to different operating conditions without requiring complex real-time simulation of all possible load scenarios.
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 more accurate and reliable estimation of the specific absorption rate with lower computational effort by decoupling the relationship between fed power and generated electromagnetic fields, using measured voltage values and MR data sets to calculate the calibration factor.
Implementation Method 1
a plurality of transmitting coil elements is used for generating the radio frequency excitation field
Implementation Method 2
The tissue may accordingly heat up as a function of the respective specific absorption rate (SAR), in other words, the electromagnetic power absorbed per unit mass
Data Source
AI summary
A method is provided for calibration of a magnetic resonance device with a transmitting device for generating an excitation field. In a first acquisition phase, a first transmitting coil element is detuned, at least one second transmitting coil element is tuned, and an MR data set is acquired using the transmitting device. In a second acquisition phase, the first transmitting coil element, the at least one second transmitting coil element are tuned, and at least one further MR data set is acquired using the transmitting device. By an arithmetic unit, a calibration factor is determined based on the MR data set and the at least one further MR data set for calculating a total voltage value at a feeding point of the first transmitting coil element from voltage values, which may be measured at a measuring point of an electrical supply line of the first transmitting coil element.