MRI SAR Calculation Using Coil Correction Coefficients
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Solution Overview
Problem
The existing pulse energy method for calculating the Specific Absorption Rate (SAR) in Magnetic Resonance Imaging (MRI) often overestimates the SAR, leading to restricted operation and reduced usability of MRI apparatuses.
Innovation Solution
A magnetic resonance imaging apparatus that calculates SAR using first and second correction coefficients, which account for the inherent characteristics of the transmitter and receiver coils, respectively, during the generation of the radio frequency magnetic field, thereby correcting for variations in transmission efficiency due to coil placement and electromagnetic coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the pulse energy method is used to calculate SAR, then the SAR calculation is simple, but the SAR is overestimated leading to restricted operation
Solution Approach 1:
The patent modifies the SAR calculation by changing the parameters used - specifically by replacing the conventional pulse energy method with a measurement-based approach using MR signal strengths at different power levels. This allows the system to determine actual transmission efficiency and electromagnetic coupling effects, thereby calculating a more accurate SAR value that prevents unnecessary operational restrictions while maintaining calculation feasibility.
2Measurement precision
If correction coefficients are introduced to improve SAR accuracy, then SAR estimation becomes more accurate, but calculation complexity increases
Solution Approach 1:
The system performs self-characterization by automatically measuring its own transmission efficiency and electromagnetic coupling effects through MR signal measurements at different power levels. The correction coefficients are determined through self-testing procedures where the MRI apparatus measures its own performance characteristics and stores these for future SAR calculations, eliminating the need for external calibration or complex manual setup.
Solution Approach 2:
The patent implements preliminary measurement steps where the system characterizes its transmission efficiency and coupling effects before actual SAR calculation. By pre-determining correction coefficients through initial measurements at different power levels, the system prepares accurate calibration data that simplifies subsequent SAR calculations rather than complicating them during real-time operation.
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 a more accurate estimation of SAR without overestimation, enhancing the usability of MRI apparatuses by avoiding excessive operational restrictions.
Implementation Method 1
excites a spin in an atomic nucleus of a subject placed in a static magnetic field by an RF (Radio Frequency) pulse of the Larmor frequency
Implementation Method 2
a second correction coefficient which indicates a characteristic that the receiver coil has on the radio frequency magnetic field by electromagnetic coupling between the receiver coil and the radio frequency magnetic field
Data Source
AI summary
According to one embodiment, a MRI apparatus includes a transmitter coil generating a RF magnetic field, a receiver coil, and processing circuitry. The receiver coil receives a MR signal generated by an object placed in an imaging space to which the RF magnetic field is applied. The processing circuitry calculates a specific absorption rate by using a first correction coefficient which indicates a characteristic that is inherent to the transmitter coil and relates to the generation of the RF magnetic field, and a second correction coefficient which indicates a characteristic that the receiver coil has on the RF magnetic field by electromagnetic coupling between the receiver coil and the RF magnetic field during a generation period of the RF magnetic field.