US 4,679,561 AGranted

Implantable apparatus for localized heating of tissue

AssigneeThe United States of America as represented by the United States Department of Energy

InventorJames D. Doss

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Abstract

With the object of repetitively treating deep-seated, inoperable tumors by hyperthermia as well as locally heating other internal tissue masses repetitively, a receiving antenna, transmission line, and electrode arrangment are implanted completely within the patient's body, with the receiving antenna just under the surface of the skin and with the electrode arrangement being located so as to most effectively heat the tissue to be treated. An external, transmitting antenna, driven by an external radio-frequency energy source, is closely coupled to the implanted receiving antenna so that the energy coupled across the air-skin interface provides electromagnetic energy suitable for heating the tissue in the vicinity of the implanted electrodes. The resulting increase in tissue temperature may be estimated by an indirect measurement of the decrease in tissue resistivity in the heated region. This change in resistivity appears as a change in the loading of the receiving antenna which can be measured by either determining the change in the phase relationship between the voltage and the current appearing on the transmitting antenna or by measuring the change in the magnitude of the impedance thereof. Optionally, multiple electrode arrays may be activated or inactivated by the application of magnetic fields to operate implanted magnetic reed switches.

An apparatus for locally increasing the temperature of living tissue located inside of a body, said apparatus comprising in combination:

a. means disposed externally to the body for generating radio-frequency electromagnetic energy having a chosen intensity;
b. first antenna means for receiving and for radiating the radio-frequency electromagnetic energy from said means for generating radio-frequency electromagnetic energy, said first antenna means being adapted for placement at substantially the closest location external to the body to the tissue to be heated;
c. second antenna means closely coupled to said first antenna means for receiving the radiated electromagnetic energy and for generating an alternating voltage therefrom having a first electrical connection and a second electrical connection, said second antenna means being adapted for location within the body near an accessible outer surface thereof in order to facilitate receiving the radiated electromagnetic energy, whereby the alternating voltage appears between said first electrical connection and said second electrical connection;
d. at least one first electrode means being in electrical contact with said first electrical connection and at least one second electrode means being in electrical contact with said second electrical connection for receiving the alternating voltage appearing between said first electrical connection and said second electrical connection of said second antenna means, said at least one first electrode means and said at least one second electrode means being adapted for location within the tissue to be heated in the vicinity of at least one of said first electrode means and said second electrode means causing thereby an increase in temperature therein;
and
e. means for externally measuring the voltage current characteristics of said first antenna means for determining the increase in temperature within the tissue to be heated, said means for externally measuring the voltage current characteristics of said first antenna means having parametric dependence on the change in electrical resistance within the tissue to be heated resulting from the increase in temperature therein.

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Abstract

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