MRI Q-Value Correction for Multi-Channel SAR Management
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Solution Overview
Problem
Magnetic Resonance Imaging (MRI) apparatuses with multiple RF channels face challenges in accurately calculating the Q value and Specific Absorption Rate (SAR) due to coupling between channels, leading to overestimation of subject consumed power, which restricts RF signal irradiation and affects image acquisition time and quality.
Innovation Solution
A magnetic resonance imaging apparatus equipped with a high-frequency antenna having multiple channels, a supply unit for different frequency signals, a measuring instrument for forward and reflected wave amplitudes, a Q-value calculation unit that fits the absolute value of the reflection matrix to a circuit model, and a Q-value correction unit to accurately calculate and correct Q values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If multiple RF channels are used to achieve spatial uniformization of irradiation, then irradiation uniformity is improved, but coupling between channels occurs causing Q value measurement errors
Solution Approach 1:
The patent segments the Q value measurement process into two distinct parts: measuring the apparent Q value that includes coupling effects, and then separately calculating the coupling correction amount based on the coupling coefficient. This segmentation allows each part to be handled independently, resolving the contradiction between using multiple channels for uniformity and avoiding their coupling interference in measurements.
Solution Approach 2:
The patent introduces the coupling coefficient as an intermediary parameter that quantifies the interaction between channels. By measuring this intermediate quantity and using it to calculate a correction amount, the patent mediates between the apparent Q value (which includes coupling effects) and the true Q value (which excludes coupling effects), thereby resolving the measurement accuracy issue while maintaining multi-channel operation.
2Ease of manufacture
If Q value is calculated using conventional methods in multi-channel systems, then calculation is simple, but subject consumed power is overestimated leading to restricted RF irradiation
Solution Approach 1:
The patent performs preliminary measurement of the coupling coefficient between channels before calculating the Q value. This preliminary action allows the system to prepare the correction data in advance, so that when calculating subject consumed power, the accurate Q value can be used without complicating the overall calculation process. The correction amount is pre-calculated based on the coupling coefficient, maintaining ease of implementation while improving accuracy.
3Measurement precision
If coupling correction is applied to Q value calculation, then SAR management accuracy is improved, but apparatus complexity increases
Solution Approach 1:
The patent implements a feedback mechanism where the coupling coefficient is measured and used to calculate a correction amount that is then applied to the apparent Q value. This feedback loop continuously refines the Q value measurement by incorporating information about channel interactions, improving SAR management accuracy without requiring fundamental changes to the apparatus architecture.
Solution Approach 2:
The system uses its own existing measurement capabilities to measure the coupling coefficient and perform the correction calculation. The MRI apparatus leverages its built-in RF signal generation and detection systems to self-determine the coupling effects and automatically correct for them, avoiding the need for external specialized equipment and keeping the apparatus complexity manageable.
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 accurate SAR management without complicating the apparatus or extending processing time, avoiding overestimation of SAR calculation values and ensuring precise power distribution to the subject.
Implementation Method 1
a high frequency antenna 103 which resonates at a predetermined frequency
Implementation Method 2
irradiates a subject disposed in a uniform static magnetic field generated by a static magnetic field magnet with a high frequency signal (hereinafter referred to as 'RF signal') being an electromagnetic wave to excite nuclear spins in the subject
Implementation Method 3
a measuring instrument 202 which measures amplitudes of a forward traveling wave and a reflected wave of each of the high frequency signals supplied from the supply unit 212 to the high frequency antenna 103
Implementation Method 4
a Q-value calculation unit 213 which calculates Q values of the plural channels of the high frequency antenna 103
Implementation Method 5
a Q-value correction unit 213A which corrects the apparent Q value Qappear to calculate the original Q value Q0
Implementation Method 6
receives an NMR signal being an electromagnetic wave generated by the nuclear spins to perform its signal processing
Data Source
AI summary
To avoid the complication of an MRI apparatus and avoid the overestimation of a calculated value of SAR without extending a processing time and to perform accurate SAR management. To this end, the MRI apparatus is equipped with a high frequency antenna which has a plurality of channels and resonates at a predetermined frequency, and a measuring instrument which measures the amplitudes of a forward traveling and reflected waves of each high frequency signal supplied to the high frequency antenna. In the MRI apparatus, a reflection matrix S is determined based on the measured amplitudes. Diagonal terms of the determined reflection matrix S are used to calculate Q values for each of the channels. Each non-diagonal term of the reflection matrix S is used to correct the calculated Q value. The corrected Q value is used to calculate irradiation power consumed in a subject among irradiation power from the high frequency signals supplied to the high frequency antenna when imaging to thereby manage a specific absorption rate.