Gradient Amplifier H-Bridge Soft Stop Against Cardiac Stimulation
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Solution Overview
Problem
Magnetic resonance (MR) systems with gradient power amplifiers face challenges in preventing nerve and cardiac stimulation due to rapid magnetic flux changes, leading to potential harm, and existing monitoring systems lack comprehensive safeguards against failures beyond power outages.
Innovation Solution
Implementing a self-locking output stage with an H-bridge configuration using non-inverting and inverting power drivers to ensure a soft stop in case of actuating signal failure, providing galvanic isolation and delaying switching to prevent damage, while maintaining a gradient field strong enough to influence heartbeats.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a hard stop is implemented by switching off all output stage switching elements, then current reduction achieves greatest possible edge steepness, but cardiac stimulation is triggered
Solution Approach 1:
The output stage is designed with two independent control paths (first control signal and second control signal) that can be activated in advance to prepare for a soft stop. The first control signal path includes switching elements that can be activated before the second control signal path, allowing the system to begin current reduction in a controlled manner before complete shutdown, thereby avoiding cardiac stimulation while maintaining fast response capability.
2Object-affected harmful factors
If a soft stop is implemented to prevent cardiac stimulation, then current reduction is achieved safely, but response time increases and gradient field strength is reduced
Solution Approach 1:
The output stage employs dynamic control with two distinct control signal paths that can operate at different speeds. The first control signal path with its switching elements can be activated rapidly for immediate response, while the second control signal path provides sustained control. This dynamic architecture allows the system to achieve both fast initial response and safe sustained current reduction, balancing response time with cardiac stimulation prevention.
3Object-affected harmful factors
If monitoring systems are added to prevent cardiac threshold crossing, then safety is improved, but device complexity increases
Solution Approach 1:
The output stage is designed with intrinsic safety features through its dual control signal path architecture. The first and second control signal paths are configured such that their switching elements naturally provide controlled current reduction without requiring external monitoring systems. The circuit itself performs the safety function through its structure, eliminating the need for additional monitoring hardware and reducing overall system complexity while maintaining cardiac stimulation prevention.
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
Prevents hard stops and damage to the output stage, ensuring safe current reduction and maintaining a strong gradient field, thereby reducing the risk of nerve and cardiac stimulation during MR system operations.
Implementation Method 1
Humans are sensitive to rapid changes in a magnetic flux dB/dt acting on them
Data Source
AI summary
A method for operating an MR system with a gradient power amplifier having at least one output stage that is connectable to a gradient coil, and having four switching elements connected to one another as an H-bridge includes, to operate the gradient coil, in alternation: switching the switching elements attached to a common first pole of a voltage supply to conductive and switching the switching elements attached to a common second pole of a voltage supply to blocking by inverting power drivers; and switching the switching elements attached to a common first pole of a voltage supply to blocking and switching the switching elements attached to a common second pole of a voltage supply to conductive by inverting power drivers. The switching elements attached to the first pole are switched by non-inverting power drivers, and the switching elements attached to the second pole are switched by inverting power drivers.