A Core Body Temperature Retrieval Method for Microwave Radiometry when Tissue Permittivity is Unknown.

Area of Science:

• Biomedical Engineering
• Electromagnetics
• Thermal Science

Background:

• Accurate core body temperature monitoring is crucial for patient care.
• Existing noninvasive methods struggle with population variations in tissue electromagnetic and thermal properties, leading to unacceptable errors.
• Pennes' bioheat model and electromagnetic simulations are foundational for understanding heat transfer and wave propagation in biological tissues.

Purpose of the Study:

• To develop and validate a novel microwave radiometry method for noninvasive core temperature retrieval.
• To address and mitigate measurement errors caused by unknown complex permittivity and heat transfer parameters in human tissues.
• To achieve a clinically acceptable measurement error (<0.5°C) across diverse patient populations.

Main Methods:

• A six-tissue-layer human head model was combined with Pennes' bioheat model and a coherent electromagnetic model.
• Nonlinear least squares optimization was employed to minimize discrepancies between simulated and experimental data.
• A Monte Carlo simulation assessed retrieval accuracy using population-representative variations in thermal and permittivity parameters across 20 frequencies (1-5 GHz).

Main Results:

• The retrieval method achieved an error of <0.1°C when only thermal parameters were unknown.
• When both thermal and permittivity parameters were unknown, the retrieval error remained <0.5°C, meeting clinical standards.
• The method demonstrated robustness against variations in antenna patterns and tissue properties.

Conclusions:

• The developed microwave radiometry method enables accurate noninvasive core temperature retrieval despite unknown tissue properties.
• This approach effectively accounts for population variations, enhancing the reliability of temperature measurements.
• The findings pave the way for clinically viable, accurate, and universally applicable noninvasive temperature monitoring using medical microwave radiometry.