Heating/sensing catheter appratus for minimally invasive applications

Abstract

Catheter apparatus comprises a coaxial cable having proximal and distal ends. The cable includes a hollow center conductor, an outer conductor and an electrically insulating layer between the conductors. An antenna is at the distal end of the cable, and a diplexer is connected to the cable, the diplexer including a transmit path for connecting the antenna to a transmitter which transmits first frequency signals and a receive path for connecting the antenna to a receiver which detects second frequency signals the diplexer isolating the signals on the two paths from one another. A transmission line connects the cable to the diplexer, the transmission line having a segment with a tubular inner conductor one end of which is connected to the center conductor and a second end of which is adapted for connection to a coolant source, the center and inner conductors forming a continuous coolant pathway.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]The present application claims priority from U.S. Provisional Patent Application No. 61 / 635,348 filed Apr. 19, 2012 by Kenneth L. Can for an INTEGRATED MICROWAVE CATHETER AND CABLE and is a continuation of copending U.S. patent application Ser. No. 13 / 709,434, which was filed on Dec. 10, 2012, by Kenneth L. Carr for a HEATING / SENSING CATHETER APPARATUS FOR MINIMALLY INVASIVE APPLICATIONS, and is hereby incorporated by reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]This invention relates to medical catheter apparatus for minimally invasive applications. It relates especially to catheter apparatus which utilizes electromagnetic radiation to simultaneously controllably heat, and detect the temperature of, fluid or tissue in a human or animal body. The apparatus includes an antenna catheter which is essentially a long flexible cable having a distal end or probe containing an antenna. In order to perform its function...

AI Technical Summary

Benefits of technology

[0013]Accordingly, it is an object of the present invention to provide an improved microwave heating / sensing catheter apparatus for minimally invasive applications.

[0016]Yet another object of the invention is to provide apparatus of this type whose antenna catheter has minimal insertion loss.

[0022]To enable the catheter to heat (transmit) and detect temperature (radiometrically sense) simultaneously, a passive diplexer is provided at the proximal end of the cable, the cable and diplexer forming a unique assembly which also allows for cooling of the cable. That is, to minimize component insertion loss, the cable / diplexer assembly provides a reduced cable impedance as well as a fluid path for a coolant delivered from the control unit to the catheter.

[0023]Even when the catheter is to be introduced into larger body passages and thus may include an internal diplexer and radiometer as described in the above patent, it is desirable that the catheter apparatus include this special cable to prevent excessive heating of the cable by the transmitter.

[0024]As will be described in more detail later, the cable has a hollow center conductor and a relatively low cable impedance, e.g. 30 ohms, compared to the usual 50 ohms. Lowering the cable impedance lowers its insertion loss because, for a given cable outside diameter, the cable's center conductor may be larger, thus increasing its conducting surface area and lowering the current density in that conductor. The hollow center conductor also provides a passage for the aforementioned coolant. The cable's center conductor is surrounded by insulation in the form of one or more filament strands wrapped around the center conductor. These strand(s) improve cable flexibility, while creating spaces that reduce the cable's dielectric constant and thus its insertion loss. These spaces may also provide a return path for a gaseous coolant whose temperature may be controlled to maintain the center conductor at a constant, safe temperature regardless of the level of applied power to the antenna in the catheter thereby to enhance the radiometric sensing capability of the apparatus.

Problems solved by technology

However, that solution rigidifies the catheter probe and places a lower limit on its diameter making it more difficult to thread the catheter along narrower blood vessels in the body and around sharp turns in such vessels and in other body passages.

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