Microwave radiometry in living tissue: what does it measure?

Area of Science:

• Electromagnetics
• Radiometry
• Biomedical Engineering

Background:

• Subcutaneous target detection is crucial for medical diagnostics.
• Microwave radiometry offers a non-invasive sensing modality.
• Understanding radiometer sensitivity to subsurface properties is essential.

Purpose of the Study:

• To investigate the sensitivity of microwave radiometry for detecting subcutaneous targets.
• To theoretically and experimentally analyze the radiometer's response to target variations.
• To evaluate the influence of dielectric properties and temperature on detection.

Main Methods:

• Experimental setup using a 4.7 GHz radiometer with a dielectric loaded waveguide antenna.
• Theoretical analysis including quasi-static approximation and bioheat equation modeling.
• Varied target location, dielectric properties, and temperature in a lossy dielectric medium.

Main Results:

• Radiometric signal is sensitive to target temperature averaged over the antenna's field pattern, with higher sensitivity near the surface.
• Quasi-static analysis effectively predicts sensitivity for targets with differing dielectric properties.
• Thermal conduction effects significantly alter the apparent size of subsurface targets.

Conclusions:

• Microwave radiometry demonstrates potential for detecting subcutaneous targets based on thermal and dielectric contrasts.
• The study provides insights into optimizing radiometer design and data interpretation for improved subsurface sensing.
• Further research is needed to fully account for complex thermal interactions in biological tissues.