Tissue dielectric measurement using an interstitial dipole antenna

Area of Science:

• Biomedical Engineering
• Electromagnetics
• Medical Physics

Background:

• Microwave tumor ablation requires precise monitoring of tissue changes.
• Existing dielectric property measurement techniques can be invasive or interrupt treatment.
• Developing non-invasive, real-time monitoring methods is crucial for effective ablation.

Purpose of the Study:

• To develop and validate an interstitial dipole antenna technique for measuring dielectric properties of biological tissues.
• To enable real-time monitoring of tissue changes during microwave tumor ablation.
• To utilize the existing heating antenna for dielectric measurements without additional procedures.

Main Methods:

• Utilized an interstitial dipole antenna to measure reflection coefficients.
• Employed a rational function model of antenna input admittance to calculate complex permittivity.
• Calibrated measurements using three referencing liquids.
• Validated the technique ex vivo on normal and ablated bovine liver tissue.
• Compared results with open-ended coaxial cable measurements (0.5-20 GHz).

Main Results:

• Dielectric properties (relative permittivity, effective conductivity) were lower in ablated zones compared to normal tissue.
• The dipole technique showed a mean 10% difference in permittivity compared to coaxial probes.
• Cole-Cole dispersion model fitting helped smooth variability in measured permittivities.

Conclusions:

• The interstitial dipole antenna technique is a viable method for measuring dielectric properties of biological tissues.
• This technique shows potential for real-time monitoring of microwave tumor ablation.
• Further development could integrate this into treatment applicators for enhanced procedural control.