Saline-Enhanced RF ablation of liver tumors

Saline Enhanced Radiofrequency Ablation: Basic Theory

Thermal therapy is used in many medical treatments, including liver cancer ablation and myocardial ablation for tachycardia.  Hyperthermic therapies use radiofrequency, ultrasound or microwave energy to heat tissue to therapeutic temperatures.  The ablation tools are typically placed near the center of the volume to be heated.  The tissue converts the incident energy to heat through absorption and, because the heating fields tend to be diverging, the tissue heating is greatest near the therapy tool.  As an example, the tissue heating at the interface of a 4 mm diameter radiofrequency electrode is 150 times greater than that in the tissue only 5 mm from the electrode surface. The small heating fields typical of these techniques are not able to treat large liver tumors or tachycardia resulting from myocardial infarct.  In order to treat these conditions one must heat 4-5 cm diameter volumes of tissue to therapeutic temperature.  Thermal conduction is insufficient to heat such large volumes of tissue using conventional ablation tools.  Thermal conduction, by itself, is only capable of carrying 0.6 W into the tissue

We use the simultaneous injection of warm saline through the therapy tool and into the tissue to convect thermal energy deep into tissue.  The saline flowing through the extracellular space is heated by the ablation energy.  The warmed saline then convects the thermal energy into the deeper tissue, which it heats to therapeutic levels.  In stark contrast to conduction alone, convection can carry 35 W through the tissue.  Using this method we have been able to therapeutically heat volumes of tissue that are 100 times larger than what radiofrequency heating alone is capable of.

Project History

Saline Enhanced Radiofrequency Ablation of liver tumors was funded by the National Institutes of Health through a Small Business Innovative Research Grant (CA69926).  The Phase 2 application is currently under review.  A second Phase 1 grant applying this to treatment of tachycardia is pending with a score of 199.

Intellectual Property

EP Limited has received United States patent number 6,328,735, Thermal ablation system.

We have also developed other methods to improve the uniformity of tissue heating during radiofrequency ablation.  Finally, we have developed methods for applying the saline enhancement technique to other heating modalities used for ablation therapy (e.g. laser, ultrasound, microwave).

In addition, we have developed a thermal model for saline enhancement of tissue heating.  Analysis using this model has led to a keener understanding of extracellular thermal convection.  As a result, we have defined heating protocols that take maximal advantage of this therapy.  We are currently holding this intellectual property as trade secret.