MRI RF Amplifier Parallel Impedance Matching for Load Variations
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Solution Overview
Problem
Conventional MRI systems use high-power isolators to manage load changes in RF amplifiers due to objects within the RF coil, which are large, expensive, and limited in output, affecting output characteristics.
Innovation Solution
The amplifying apparatus employs two amplification circuits in parallel with impedance transformation circuits using quarter-wavelength transmission lines to stabilize output characteristics by adjusting reactance polarity, eliminating the need for high-power isolators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-power isolator is provided between the RF amplifier and RF coil to suppress load changes, then the output characteristics are stabilized, but the physical size increases and cost increases
Solution Approach 1:
The patent introduces an impedance transformation circuit as an intermediary component between the RF amplifier and RF coil. This circuit transforms the varying load impedance (caused by object insertion) into a more stable apparent load for the amplifier, thereby stabilizing output characteristics without requiring a bulky high-power isolator.
Solution Approach 2:
The impedance transformation circuit dynamically adjusts impedance parameters to compensate for load variations. By changing the transformation ratio based on detected load conditions, the system maintains stable output characteristics while using a compact circuit rather than a large isolator.
2Reliability
If a high-power isolator is provided to suppress load changes, then the output characteristics are stabilized, but the cost increases
Solution Approach 1:
The patent replaces the expensive high-power isolator with a cost-effective impedance transformation circuit composed of standard RF components such as transformers, inductors, and capacitors. This circuit achieves the same stabilization function at a fraction of the cost.
Solution Approach 2:
The impedance transformation circuit serves as a cost-efficient intermediary that performs the load isolation function through impedance transformation rather than through the expensive mechanism of a high-power isolator.
3Reliability
If a high-power isolator is provided to suppress load changes, then the output characteristics are stabilized, but the maximum output is limited
Solution Approach 1:
The impedance transformation circuit adjusts the transformation ratio based on load conditions to maintain stable output characteristics across the full power range. This allows the RF amplifier to deliver maximum output power without the limitations imposed by a high-power isolator's maximum rating.
Solution Approach 2:
The system dynamically adjusts the impedance transformation ratio in response to changing load conditions, enabling the RF amplifier to operate at full power while maintaining stable output characteristics. This dynamic adaptation eliminates the fixed power limitations of a high-power isolator.
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
Stabilizes output characteristics by compensating for inductive or capacitive load changes, ensuring consistent power delivery to the RF coil without the size and cost constraints of high-power isolators.
Implementation Method 1
an impedance transformation circuit; and the impedance transformation circuit is provided between the load and an output terminal of one of the two amplification circuits such 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 the other of the two amplification circuits toward the load
Data Source
AI summary
In one embodiment, an MRI apparatus includes: an RF coil configured to apply a radio frequency (RF) signal of a Larmor frequency of a spin species in an object; and an amplifying apparatus configured to amplify the RF signal and supply the amplified RF signal to an output that is connectable to a load (80) that includes at least the RF coil and the object, wherein: the amplifying apparatus includes two amplification circuits provided in parallel and an impedance transformation circuit; and the impedance transformation circuit is provided between the load and an output terminal of one of the two amplification circuits such 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.