MMTC (United States)

A circuit that uses electronically variable time delay elements to suppress interfering signals on the basis of their difference-in-time-of-arrival at two spatially separated antennas is described. 40 dB of suppression of wideband interferers was demonstrated in cases where strong, wideband interferers overlapped the frequency of the desired signal, and where the difference in the difference-in-time-of-arrival of interferers and desired signals was as small as 30 picoseconds.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Microwave balloon catheters are plastic catheters that contain microwave transmission lines that are connected to microwave antennas located inside inflatable balloons. Provisions for liquid cooling of the balloons, ternperature sensing, suctioning, etc can be incorporated into the catheters if the intended application requires it. In medical applications the catheters are inserted with collapsed balloons into blood vessels, natural body openings, or interstially directly into tissues, the balloons are then inflated, and microwave power is applied to the transmission lines and broadcast into the tissues surrounding the balloons. While hundreds of thousands of medical procedures have already been performed with simple balloon catheters, clinical use of microwave balloon catheters is still in its Infancy. This is not surprising, since the first documented medical use of simple balloon catheters dates back to 1819, while development of medical microwave balloon catheters started only a few years ago.

A study of the technique of microwave (2.45 GHz) thermal balloon angioplasty has established a correlation between recorded temperature and observed injury. In addition, a trend pointing toward an inverse relationship between intimal proliferation and medial injury has been observed. Angioplasty was performed on 30 normal New Zealand white rabbits, providing 60 iliac arteries for histopathologic analysis. The angioplasty catheter consists of a 3.0-mm angioplasty balloon with an intrinsic thermocouple placed on the interior surface of the midportion of the balloon. A 0.023-in coaxial cable was used to deliver the microwave power, and a slot antenna configuration was chosen for the radiating element. >

Preliminary experiments on the induction of 1ocalized myocardial tissuie modification by microwave energy, without causing any cardiac arrhythmias, were the first step in the development of both microwave ablation and an innovative procedure called microwave balloon angioplasty (MBA). MBA combines the traditional angioplasty technique with microwave energy to open narrowed arteries and reduce the occurence of restenosis. Microwave balloon angioplasty was used in anesthetized rabbits to induce tissue modification in the intima, media and adventitia. Resu1ts of initial in-vitro and in-vivo experiments are presented, and the potential advantages of adding microwave heating to balloon angioplasty are discussed.