A system for detecting vulnerable arterial plaque formed on the vessel wall in vivo is disclosed. The system comprises a catheter having a proximal end and a distal end, one or more thermal sensors at said distal end of said catheter, and a detector coupled to the proximal end of the catheter and in communication with one or more of the thermal sensors. The detector is capable of receiving thermal information from one or more thermal sensors and differentiating the different types of plaque based upon the thermal information received.