Microwave Ablation

Microwave energy (usually 0.9-2.45 GHz) generates heat by rapidly oscillating water molecules and ions in biological tissues. Unlike other ablation energy sources (electrical current, lasers, ultrasound, etc), microwave energy can radiate through many types of materials, inlcuding air, water vapor and desiccated tissues by thermal ablation. As a result, microwaves can create large ablations in only a few minutes time.

Microwave ablation created in liver in vivo with a 17-gauge gas-cooled triaxial antenna.

Antenna Design

The design of the antenna used to deliver microwaves determines how efficiently and in what pattern energy is delivered. We create designs based on near-field antenna theory. The triaxial antenna developed in our lab established much of the basic foundation for modern microwave ablation, proving that large ablations can come from small antennas. More recent research has focused on creating spherical heating patterns with coaxial antennas as well as application-specific designs for small tumors, surgical applications and external heating.

Energy Application

While the antenna influences how energy is delivered, the energy delivery itself — frequency, peak power, total energy, pulsing, etc. — has not received as much research attention to date. Optimizing such parameters may lead to more effective treatments.

RF and microwave ablations created in an ex vivo liver window model. Note that the microwave ablation grows continuously over time and even causes the surrounding tissue to contract towards the antenna. The RF ablation effectively stops growing after two minutes.

System Design

Not all ablation systems are the same. Our fundamental work has shown that using multiple applicators is a more efficient method of energy delivery for large-volume ablation. We are now extending this work to develop systems capable of more reproducible and customizable ablation zones that suit many clinical applications.

Monitoring

Energy delivery is important, but interactive feedback is necessary for clinical success. We are investigating ways to monitor ablation progress without imaging, by using the ablation applicators as signal detectors.