Subnanosecond Electrical Pulses for Medical Therapies and Medical Imaging

The use of prolate-spheroidal reflectors as part of a sub-nanosecond Impulse Radiating Antenna (IRA) allows us to generate near-field electric fields with high spatial resolution in biological tissue. If the power of such ultrashort electrical pulses is very high, it becomes possible to deposit substantial electromagnetic energy into deep-lying tissue, even at the rather high conductivity and consequently strong absorption of most tissues. This electromagnetic energy may be used either to stimulate bioelectric effects, such as pulsed electric field induced apoptosis of tumor cells, or to generate local hyperthermia. Besides using ultrashort electrical pulses for medical therapies, the use of Impulse Radiating Antennas in the hundred-picosecond temporal range leads to medical imaging methods with sub-centimeter spatial resolution. The method is based on the measurement of changes in the complex permittivity of tissue, and may complement imaging methods based on the measurement of other physical parameters. For example, breast tumors are characterized by conductivity and permittivity approximately five times higher than surrounding healthy tissue. Our experimental work focuses on the design and construction of subnanosecond pulse generators, which has resulted in a 150 ps, 50 kV, 50 Ohm generator. The design of prolate-spheroidal antennas for these medical applications is pursued in cooperation with C. Baum at the University of New Mexico. A three-dimensional, time-dependent electromagnetic code (MAGIC) is used to model the electric field distribution in tissue. The pulse power research efforts are complemented by studies on the biological effect of subnanosecond electrical pulses.