Patent ID: 7933660

Claim:
Apparatus for detecting vulnerable plaques embedded or ingrained in the wall of a patient's blood vessel containing blood whose temperature is substantially the same as that of normal tissue, said apparatus comprising an intravascular catheter having proximal and distal ends and containing an outer coaxial cable forming a first antenna optimized at a first frequency to pick up thermal emissions from radially outer subsurface locations in said wall and produce a corresponding first signal and an inner coaxial cable forming a second antenna optimized at a second frequency lower than the first frequency to pick up thermal emissions from radially inner locations in said blood and produce a corresponding second signal, said first and second antennas being coaxial; first and second radiometers, operating at said first and second frequencies respectively each radiometer having an input and an output; a passive diplexer located at the proximal end of the catheter, said diplexer having a tubular inner conductor and a coaxial outer conductor, said inner conductor receiving the inner coaxial cable and the inner and outer conductors being connected electrically to the outer coaxial cable, said outer conductor having a branch oriented 90° relative to the inner conductor and spaced from corresponding shorted ends of the inner and outer conductors to form a quarter wave stub at the first signal frequency, said diplexer being connected between the antennas and the radiometers for simultaneously routing said first and second signals to the respective inputs of the first and second radiometers so that said radiometers provide at their respective outputs simultaneous first and second temperature signals, and a processor for comparing said first and second temperature signals to produce a continuous difference signal, said catheter being movable along said vessel so that at each axial location along the vessel, said difference signal indicates the presence or absence of vulnerable plaques due to the higher emissivity thereof as compared to that of the normal tissue.