MRI RF Amplifier Feedback Switching for High-Slew Pulses
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Solution Overview
Problem
The existing MRI apparatuses face image quality degradation due to the deterioration of RF pulse rise caused by feedback processing, especially when using ultrashort square waves or trapezoidal waves, which results in unstable and nonlinear RF pulse outputs.
Innovation Solution
The MRI apparatus selectively switches the feedback processing based on the slew rate of the input RF pulse, determining whether to apply correction by using a slew-rate measurement circuit and a multiplexer to decide whether to perform feedback processing, thereby preventing waveform deterioration for high slew rate pulses and ensuring stability and nonlinearity for low slew rate pulses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If feedback processing is applied to RF pulses with sharp rise (high slew rate) such as square waves or trapezoidal waves, then stability and linearity of RF pulse output are improved, but the rise of each RF pulse outputted from the amplifier is deteriorated, degrading image quality
Solution Approach 1:
The patent changes the parameter of feedback application by introducing a slew rate threshold. When the slew rate of the RF pulse exceeds this threshold, feedback processing is suppressed; when it is below the threshold, feedback processing is performed. This parameter-based conditional approach resolves the contradiction by adapting the feedback processing behavior to the specific characteristics of each RF pulse waveform.
Solution Approach 2:
The patent implements dynamic control of feedback processing based on real-time measurement of the RF pulse slew rate. The determination circuit dynamically decides whether to apply feedback processing by comparing the measured slew rate against a predetermined threshold, allowing the system to adaptively adjust feedback application according to the instantaneous characteristics of the RF pulse being generated.
2Shape
If feedback processing is suppressed for high slew rate pulses, then waveform integrity is maintained, but stability and linearity correction is lost for low slew rate pulses
Solution Approach 1:
The patent uses the slew rate parameter as a discriminant to determine the appropriate processing mode. By establishing a predetermined threshold for this parameter, the system can automatically differentiate between pulse types that require feedback processing and those that do not, thereby maintaining waveform integrity for high slew rate pulses while ensuring stability correction for low slew rate pulses.
Solution Approach 2:
The patent segments the feedback processing application into two distinct cases based on the slew rate threshold: one path for pulses with slew rate above the threshold (where feedback is suppressed to preserve waveform), and another path for pulses with slew rate below the threshold (where feedback is applied to ensure stability). This segmentation allows the system to optimize performance for different pulse types independently.
Data Source
AI summary
According to one embodiment, an MRI apparatus includes an amplifier and a control circuit. The amplifier amplifies an RF pulse and supplies it to an RF coil. The control circuit is configured to determine whether an output RF pulse outputted from the amplifier is fed back to an input side of the amplifier to correct an input RF pulse to be inputted into the amplifier, based on a determination value being set according to a slew rate of the input RF pulse.