MR Gradient Amplifier Softstop Circuit for Cardiostimulation Prevention
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Solution Overview
Problem
Magnetic resonance (MR) systems with strong gradient systems risk triggering cardiostimulation, a potentially life-threatening condition, due to rapid changes in magnetic flux, and existing monitoring systems lack comprehensive safeguards against hardstops caused by power failures or other disturbances.
Innovation Solution
The implementation of a gradstop unit within the gradient pulse amplifier, which includes lockout switches and feeder circuit breakers, generates a 'softstop' actuation pattern to prevent hardstops by locking out or actuating signal paths, ensuring a controlled reduction of gradient current and minimizing patient stimulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a hardstop is implemented to quickly reduce gradient current, then the response speed is improved, but cardiostimulation risk increases
Solution Approach 1:
The end stage switching elements are divided into two groups: first switching elements that are switched off during normal operation, and second switching elements that remain on during normal operation. During a shutdown event, the first switching elements are switched off to reduce current, while the second switching elements remain on to maintain a controlled reduction rate and prevent cardiostimulation. This segmentation allows differentiated control of different switch groups based on their specific functions.
Solution Approach 2:
Different switching elements within the end stage are assigned different operational characteristics: the first switching elements are optimized for rapid shutdown response, while the second switching elements are optimized for maintaining controlled current reduction. This local differentiation of switch characteristics enables the system to achieve both fast response and safety simultaneously.
2Object-affected harmful factors
If a softstop is implemented to reduce gradient current slowly, then cardiostimulation risk is reduced, but the response time increases
Solution Approach 1:
The end stage switching elements are segmented into first and second switching elements with different operational roles. The first switching elements provide rapid response capability when needed, while the second switching elements ensure controlled current reduction. This segmentation resolves the contradiction by having different parts of the system respond differently based on the operational context.
Solution Approach 2:
The system dynamically adjusts the operational state of different switching element groups based on the shutdown scenario. During normal operation, first switching elements are off and second switching elements are on. During shutdown, the system transitions to a state where first switching elements are switched off and second switching elements remain on, providing adaptive control that balances speed and safety.
3Speed
If all end stage switching elements are switched off during shutdown, then current reduction speed is improved, but stimulation threshold overshoot increases
Solution Approach 1:
The switching elements are segmented into first and second groups with different shutdown behaviors. First switching elements are switched off to contribute to current reduction, while second switching elements remain on to prevent excessive dB/dt changes. This segmentation prevents stimulation threshold overshoot by ensuring that not all switching elements are switched off simultaneously.
Solution Approach 2:
The second switching elements are pre-configured to remain on during shutdown events, providing a protective effect that prevents excessive magnetic flux changes. This preliminary configuration ensures that even if first switching elements are rapidly switched off, the second switching elements will counteract any potential overshoot in dB/dt.
4Reliability
If monitoring systems are enhanced to detect all failure modes, then reliability is improved, but device complexity increases
Solution Approach 1:
The gradient pulse amplifier unit performs self-monitoring by internally tracking the operational states of its switching elements and detecting anomalies such as failures in the modulator or clock-pulse supply. The system automatically responds to detected failures by initiating appropriate shutdown sequences, eliminating the need for external monitoring systems and reducing overall complexity.
Solution Approach 2:
The existing switching element control circuitry is made multi-functional by enabling it to serve both normal operation control and failure detection functions. The same hardware that controls the switching elements also monitors their operational states and triggers shutdown sequences when failures are detected, eliminating the need for separate dedicated monitoring hardware.
Data Source
AI summary
A method for operating an MR system with a gradient pulse amplifier unit that has an end stage connected to a gradient coil with switching elements is provided. The gradient pulse amplifier unit includes a modulator for actuating the switching elements, and lockout switches interconnected in signal paths from the modulator to the switching elements. The gradient pulse amplifier unit includes feeder circuit breakers interconnected in at least some signal paths from the modulator to the switching elements. The circuit breakers are connected in the associated signal paths downstream of the lockout switches. A gradstop unit configured to receive at least one shut-off signal and actuate the lockout switches and the feeder circuit breakers. When the gradstop unit receives a shut-off signal, the gradstop unit actuates the lockout switches to lock out and the feeder circuit breakers to output an actuation signal to the switching elements.