Unity Gain Buffer Amplifier for MRI Electrophysiological Signal Isolation
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Solution Overview
Problem
Concurrent MRI and electrophysiological data acquisition is hindered by electromagnetic interference (EMI) between MRI systems and electrophysiological recording devices, with high-frequency harmonics from digital signals corrupting MRI procedures and EMI from MRI systems degrading electrophysiological signals.
Innovation Solution
The use of unity gain buffer amplifiers near the patient with low output impedance, combined with passive low pass filtering, to reduce capacitively coupled interference and prevent emission of high-frequency signals, allowing electrophysiological signals to be processed outside the MRI room.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If high speed digital switching signals are used to acquire EEG waveforms in digital format, then the EEG signal can be readily transferred to a computer through standard interface, but high frequency harmonics are generated that radiate from equipment near the MRI machine and interfere with the imaging process
Solution Approach 1:
The patent extracts the analog-to-digital conversion function from the MRI room environment and places it outside. The EEG signal is converted to digital format outside the MRI room, eliminating the source of high-frequency harmonics from digital switching signals that would otherwise interfere with the MRI imaging process.
Solution Approach 2:
The patent introduces an intermediary buffering system with isolation amplifiers and passive filters that mediates between the EEG electrodes and the digital processing equipment. This intermediary system allows the EEG signal to be processed digitally without placing the digital conversion equipment inside the MRI room where it would generate interfering harmonics.
2Object-generated harmful factors
If electrode signals are sent via long cable to the EEG machine located outside the MRI room, then the EEG signal can be recorded outside the MRI room, but electrical interference from the MRI system or nearby power mains is capacitively coupled to the electrophysiological signal
Solution Approach 1:
The patent introduces isolation amplifiers as an intermediary device between the EEG electrodes and the long cable running outside the MRI room. These isolation amplifiers provide galvanic isolation that blocks the capacitive coupling of electrical interference from the MRI system and power mains, while still allowing the EEG signal to be transmitted to the recording equipment outside the MRI room.
Solution Approach 2:
The isolation amplifiers create an isolated copy of the EEG signal that can be transmitted through the long cable without carrying the interference that would be capacitively coupled to the original signal path. This copying mechanism allows the signal to be transmitted outside the MRI room while maintaining signal integrity.
3Object-affected harmful factors
If a buffer amplifier with low output impedance is used to drive the cable, then capacitively coupled interference is greatly reduced, but additional circuitry is required near the patient
Solution Approach 1:
The patent merges multiple functions into the buffering system located near the patient: the isolation amplifier provides both the low output impedance needed to drive the cable and the galvanic isolation to block interference, while also incorporating passive filtering to attenuate high-frequency MRI signals. This integration reduces the need for separate components and simplifies the overall system architecture.
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
Significantly reduces electromagnetic interference between MRI systems and electrophysiological recordings, enabling accurate and interference-free data acquisition during MRI procedures by minimizing both EMI induced in electrophysiological signals and emitted by digital conversion processes.
Implementation Method 1
Passive low pass filtering may be incorporated prior to the buffer amplifier to attenuate high frequency interference from the MRI system
Implementation Method 2
The low output impedance of the buffer amplifier allows long cable runs with significantly reduced capacitively coupled interference from the MRI machine or nearby mains power wiring
Data Source
AI summary
The subject invention overcomes the problem of electrical interference in signals taken during an MRI procedure by using a long cable and a unity gain buffer amplifier near the patient, with a low output impedance to drive the cable and thus greatly reduce the capacitively coupled interference. Passive low pass filtering is incorporated prior to the buffer amplifier to attenuate high frequency interference from the MRI system. Since the buffer amplifier requires no digital signals and does not emit high frequency signals, it does not interfere with the MRI system.