ablation of liver tumors
Enhanced Radiofrequency Ablation: Basic Theory
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.
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.
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.