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Initial in vivo experience with EIT as a thermal estimator during hyperthermia
K D Paulsen1, M J Moskowitz, T P Ryan
1Thayer School of Engineering, Dartmouth College, Hanover, NH, USA.
Summary
Electrical impedance tomography (EIT) shows potential for monitoring hyperthermia treatments by reconstructing conductivity changes. While correlations with temperature exist, the complex tissue impedance-temperature relationship requires further investigation for precise thermal estimation.
Area of Science:
- Biomedical Engineering
- Medical Imaging
- Oncology
Background:
- Hyperthermia therapy involves heating tissue to treat diseases like cancer.
- Accurate temperature monitoring during hyperthermia is crucial for treatment efficacy and patient safety.
- Electrical impedance tomography (EIT) offers a non-invasive method for imaging physiological changes.
Purpose of the Study:
- To investigate the feasibility of using EIT for real-time monitoring of thermal changes during hyperthermia treatments.
- To assess the accuracy of EIT in estimating temperature distributions in human and animal subjects undergoing hyperthermia.
- To explore the relationship between electrical conductivity changes and temperature variations in biological tissues.
Main Methods:
- Experiments were conducted on two human patients and one animal subject undergoing hyperthermia.
- A 16 or 32-electrode array was used to inject 12.5 KHz current patterns and record potential distributions.
- Image reconstruction was performed using a finite element method to generate conductivity difference images.
- Linear and nonlinear relationships between tissue impedance and temperature were applied for thermal image generation.
Main Results:
- Reconstructed conductivity changes were successfully obtained in vivo during hyperthermia treatments.
- EIT-derived thermal images showed good correlation with direct temperature measurements.
- Estimated temperature accuracies were approximately 1.5 degrees C, with some larger errors exceeding 5 degrees C.
- The study confirmed the possibility of using electrical data for thermal monitoring.
Conclusions:
- EIT is a promising tool for monitoring and assessing hyperthermia treatments.
- The complex, nonlinear relationship between tissue impedance and temperature presents challenges for direct thermal estimation.
- Further research is needed to refine EIT's role as a thermal estimator or explore its use as a fundamental indicator of thermal effects.