Wireless Transmitter for MRI ECG Signal Safety
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Solution Overview
Problem
Magnetic Resonance Imaging (MRI) systems face challenges in accurately detecting the ECG 'R' wave due to strong static magnetic fields, induced currents in conductive blood, moving magnetic gradients, and high-power pulsed RF fields, which distort signals and pose safety risks for patient leads.
Innovation Solution
A wireless transceiver system with a magnetic field tolerant amplifier, RF cancellation delay line, and flexible patient leads with distributed impedance, utilizing a 2.4 GHz RF transceiver for signal transmission and processing to minimize artifacts and ensure safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional patient leads and cables are used to bring ECG signal out of MRI bore, then ECG signal can be transmitted to amplifiers, but signal artifacts are generated in the same bandwidth as ECG signal due to moving magnetic gradients
Solution Approach 1:
The patent extracts the ECG signal acquisition function from the traditional wired lead system and places it directly on the patient's body using integrated electrodes. This removes the cables that generate artifacts in the MRI bore, separating the signal source from the harmful electromagnetic environment while maintaining signal transmission capability through wireless or alternative pathways.
Solution Approach 2:
The patent introduces specialized MRI-compatible electrodes and leadless signal conditioning circuits as intermediaries between the patient's body and the ECG amplification system. These intermediaries are designed to be non-conductive or have distributed impedance to prevent artifact generation while still allowing the ECG signal to pass through to external amplifiers.
2Measurement precision
If patient leads are exposed to high-power pulsed RF fields in MRI, then ECG signal can be transmitted, but eddy currents are generated in looped wires causing heating and third degree burns
Solution Approach 1:
The patent removes the traditional wired patient leads from the MRI environment entirely, replacing them with wireless transmission or fiber optic cables that do not conduct electricity. This extracts the signal transmission function from the conductive wire medium that generates dangerous eddy currents in the RF field, eliminating the heating hazard while preserving ECG monitoring capability.
Solution Approach 2:
The patent employs disposable, single-use MRI-conditional electrodes and leadless sensors that are designed to be discarded after one use. These disposable components are engineered with safety features inherent to their construction, eliminating the need for complex safety mechanisms and ensuring patient safety without compromising signal transmission quality.
3Object-affected harmful factors
If distributed impedance of about 10Kohms/ft is used in patient leads to limit eddy current generation, then patient safety is improved, but electrical noise of the system increases
Solution Approach 1:
The patent replaces the electrical wire-based signal transmission system with alternative physical media such as fiber optic cables or wireless RF transmission. This substitution eliminates the need for distributed impedance management entirely, as the new transmission medium does not conduct electricity and therefore cannot generate eddy currents or associated electrical noise, solving both problems simultaneously.
Solution Approach 2:
The patent fundamentally changes the impedance parameter of the transmission medium from high (10Kohms/ft) to effectively infinite (non-conductive) by using fiber optic or wireless transmission. This parameter change eliminates the trade-off between safety and noise, as the new medium provides both safety through non-conductivity and low noise through immunity to electromagnetic interference.
4Object-affected harmful factors
If non-metallic electrodes are used to avoid magnetic projectile effects, then patient safety is improved, but signal quality may be compromised in the strong static magnetic field
Solution Approach 1:
The patent employs composite electrode materials that combine non-conductive, non-magnetic substrates with conductive trace patterns or embedded wires. These composite structures provide the mechanical flexibility and safety of non-metallic materials while incorporating conductive pathways optimized for ECG signal acquisition, achieving both safety and signal quality through material composition rather than simple non-metallic construction.
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 cancels RF interference, reduces signal distortion, and ensures safe ECG signal transmission within MRI environments, providing accurate cardiac gating for MRI and other imaging procedures without the need for extensive post-processing.
Implementation Method 1
An RF cancellation delay line circuit having a pair of output terminals is provided. Each output terminal of the RF cancellation delay line circuit is connected to a respective input terminal of the amplifier stage.
Implementation Method 2
An amplifier stage having a pair of differential input terminals and a pair of differential output terminals is provided.
Implementation Method 3
A differential to single ended output amplifier stage is provided. Each input terminal of the differential to single ended output amplifier stage is connected to a respective output terminal of the amplifier stage.
Implementation Method 4
An A/D converter is provided. The output of the differential to single ended amplifier stage is connected to an input terminal of the A/D converter.
Implementation Method 5
A 2.4 GHz RF transceiver is provided. An output terminal of the A/D converter is connected to an input terminal of the 2.4 GHz RF transceiver.
Data Source
AI summary
A magnetic field tolerant amplifier having an amplifier stage, a differential to single-ended output amplifier stage and a first and second delay line. In another embodiment the invention relates to a magnetic gradient cancellation delay line including two coils connected in series at a junction and non-inductively wound to cancel induced currents from magnetic gradient. In another embodiment the invention relates to a patient lead including a flexible circuit substrate having a flexible conductor having distributed impedance. In still yet another embodiment the invention relates to a wireless transceiver system including an RF cancellation delay line; a differential amplifier stage; a differential to single ended output amplifier stage; an A/D converter; an RF transceiver and an antenna.