Local Coil Detuning Circuits for MRI Safety
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Magnetic resonance tomography scanners pose safety risks due to high magnetic alternating fields that can cause thermal and electrical effects, particularly endangering patients with implants, and existing technologies lack effective measures to mitigate these risks during excitation pulses.
Innovation Solution
The implementation of a local coil system with both active and passive detuning facilities, utilizing separate circuits and components to vary the resonance frequency and limit induced signal amplitudes, ensuring safe operation by preventing dangerous resonances even in case of individual component failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single detuning facility is used in the local coil, then the device complexity is reduced, but the reliability deteriorates because a single point of failure can cause resonance at Larmor frequency
Solution Approach 1:
The patent applies local quality by implementing two distinct detuning facilities with different functional characteristics: an active detuning facility that can be controlled to detune the resonance circuit, and a passive detuning facility that provides inherent detuning capability. Each facility has its own circuitry and operates independently, ensuring that a failure in one does not compromise the overall safety against resonance at Larmor frequency.
2Object-affected harmful factors
If active detuning facility is activated during excitation pulses, then the harmful effects are reduced, but the device complexity increases due to additional control circuits
Solution Approach 1:
The patent implements preliminary action by activating the active detuning facility before the excitation pulse is applied. The control circuit receives a control signal and activates the detuning facility in advance, ensuring that the resonance circuit is already detuned when the high-power excitation pulse occurs, thereby preventing thermal and electrical harmful effects before they can manifest.
Solution Approach 2:
The patent employs feedback mechanisms where the control circuit monitors the state of the local coil and adjusts the active detuning facility accordingly. The control circuit receives feedback signals about the resonance conditions and modifies the detuning activation to maintain safety while minimizing unnecessary complexity in the control structure.
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
The system effectively dampens induced signal amplitudes by more than 20 dB, reducing the risk of thermal and electrical effects, ensuring patient safety by preventing harmful resonances and maintaining system functionality even with component failures.
Implementation Method 1
In particular, a circuit, which actuates an active detuning facility of a local coil and thus, controlled by a controller of the magnetic resonance tomography scanner, may purposefully detune the local coil or may also restore it to the resonance frequency, is regarded as a local coil actuation here. This may be achieved in that in the local coil, a PIN diode is provided in the antenna circuit. This reduces the capacitance by way of a voltage applied by the local coil actuation and thus detunes the antenna circuit.
Implementation Method 2
For detuning or damping, the passive detuning facility uses the induced voltage and limits it to a safe value, (e.g., less than 2V, 5V, 10V, or 20V).
Implementation Method 3
A circuit in the local coil is referred to as an active detuning facility in this connection, which varies a resonance frequency of the local coil in response to an actuation signal, so it is no longer resonant at a Larmor frequency of the magnetic resonance tomography scanner. The resonance frequency of the local coil is varied by the activated active detuning facility to the extent that an amplitude of an induced signal with Larmor frequency of the magnetic resonance tomography scanner is damped by more than 20 dB, 40 dB, 60 dB, or 80 dB with respect to the amplitude without active or passive detuning.
Data Source
AI summary
A local coil, a magnetic resonance tomography scanner, a system including local coil and magnetic resonance tomography scanner, and a method for operating the system are provided. The local coil has an active detuning facility and a passive detuning facility with substantially separate circuits. The magnetic resonance tomography scanner includes a local coil actuation for actuating the active detuning facility and a local coil monitoring for the detuning facilities, which likewise have substantially separate circuits.