MRI RF Amplifier Impedance Conversion for Load Mismatch Stability
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Solution Overview
Problem
Conventional MRI systems face challenges with load changes in RF amplifiers due to factors like object physique, posture, and motion, leading to inefficiencies and the need for large, expensive high-power isolators to manage load mismatches.
Innovation Solution
The implementation of a parallel element circuit configuration in the RF amplifier, utilizing impedance conversion circuits to stabilize output characteristics by adjusting reactance polarities and distributing heat generation across multiple amplification circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-power isolator is provided between the output terminal of the RF amplifier and the RF coil to suppress the influence of load changes, then the stability of the amplification circuits is improved, but the device size increases and the cost increases
Solution Approach 1:
The patent divides the single amplification system into multiple amplification circuits (first and second amplification circuits) operating in parallel. Each circuit handles a portion of the total power, and their combined output delivers the required high power to the load. This segmentation eliminates the need for a high-power isolator while maintaining system stability.
Solution Approach 2:
The patent combines the outputs of multiple amplification circuits through a combiner to achieve the desired total output power. By merging the signals from multiple lower-power circuits, the system reaches high-power levels without requiring a single high-power component that would necessitate a large isolator.
2Reliability
If a high-power isolator is used to protect the amplification circuits from load mismatch, then the reliability is improved, but the maximum output capability is limited
Solution Approach 1:
By segmenting the amplification system into multiple parallel circuits, each circuit operates at a lower power level where load mismatch has less impact. The individual circuits can maintain stable operation without requiring a high-power isolator that would limit the overall system output capability.
Solution Approach 2:
The patent introduces a combiner as an intermediary device that merges the outputs of multiple amplification circuits. This combiner provides impedance transformation and signal combining functionality, enabling the system to achieve high power output while protecting individual circuits from the full burden of load variations.
3Power
If multiple amplification circuits are used in parallel to deliver high power, then the power output capability is improved, but the heat generation imbalance increases
Solution Approach 1:
The patent applies different impedance conversion ratios to different amplification circuits based on their individual characteristics and operating conditions. By locally optimizing the impedance matching for each circuit, the system balances the power distribution and heat generation across all circuits, preventing thermal imbalance while maintaining high total power output.
Solution Approach 2:
The system dynamically adjusts operating parameters such as impedance conversion ratios and power distribution for each amplification circuit. By changing these parameters based on real-time conditions, the system optimizes heat generation balance across parallel circuits while maintaining the required total power output capability.
Data Source
AI summary
In one embodiment, an MRI apparatus comprising an amplifying apparatus configured to supply an amplified RF signal to a load, wherein the amplifying apparatus comprises a plurality of parallel element circuits, each of which includes two amplification circuits installed in parallel and an impedance conversion circuit provided between the load and an output terminal of at least one of the two amplification circuits. The impedance conversion circuit is configured in such a manner that; a polarity of reactance as viewed from an output terminal of one of the two amplification circuits toward the load is opposite to a polarity of reactance as viewed from an output terminal of another of the two amplification circuits toward the load; and impedance as viewed from the output terminal of at least one of the two amplification circuits toward the load via the impedance conversion circuit differs between the plurality of parallel element circuits.