A review of errors in multi-frequency EIT instrumentation

Area of Science:

• Biomedical Engineering
• Medical Imaging
• Electrical Engineering

Background:

• Multi-frequency electrical impedance tomography (MFEIT) has been explored for over a decade as a spectroscopic impedance imaging technique.
• Despite the development of seven systems for imaging organs like the lung, heart, breast, and brain, none have achieved widespread clinical acceptance.
• Significant instrumentation requirements exist for MFEIT systems to maintain a stable frequency response across a broad frequency range (DC-MHz) due to small physiological spectral changes.

Purpose of the Study:

• To analyze the multi-frequency electrical impedance tomography (MFEIT) measurement problem.
• To review solutions for common MFEIT challenges and revisit the architecture debate (four-terminal vs. two-terminal).
• To identify major sources of error in MFEIT systems.

Main Methods:

• Described the EIT measurement problem from a multi-frequency perspective.
• Considered solutions from recent MFEIT systems.
• Analyzed sources of MFEIT errors, focusing on stray capacitance and common-mode voltages.

Main Results:

• Identified stray capacitance and common-mode voltages as major error sources in MFEIT.
• These errors cause a load-dependent frequency response in MFEIT systems.
• Systems utilizing active electrodes demonstrated a greater ability to mitigate these errors.

Conclusions:

• Active electrode systems are most effective in managing MFEIT errors.
• A distributed system with electrode-level digitization is proposed as a future development direction for MFEIT.
• Further advancements are needed to overcome current limitations and achieve clinical acceptance for MFEIT.