An optical thermal device and methods for monitoring temperature and detection of a vulnerable plaque of a patient comprising an elongate tubular element comprising at least one optical fiber; the fiber having at least one optical grating along an axis of the fiber; and a light source having a light beam that is coupled into the at least one optical fiber; wherein the optical grating reflects a certain wavelength or intensity of the light beam, the certain wavelength or intensity of the reflected light beam being correlated to the temperature of the tissue regions.