  ABSTRACT: Temperature monitoring is extremely im-portant during
thermotherapy. Fiber-optic temperature sensors are preferred because of their
flexibility and im-munity to electromagnetic interference. Although many types
of fiber-optic sensors have been developed, it re-mains challenging for
clinically adopting them. Here, we report a silica fiber-based radiometric
thermometer using a low-cost extended InGaAs detector to detect black body
radiation between 1.7um to 2.4 um. For the first time, this silica fiber-based
thermometer is capable of measuring temperature down to 35{\deg}C, making it
suitable for seamless integration with current silica fiber catheters used in
laser interstitial thermotherapy to monitor hyperthermia during a surgery. The
feasibility, capability, and sensitivity of track-ing tissue temperature
variation were proved through ex vivo and in vivo tissue studies. The
technology is promising for being translated into clinics after further
improving the signal to noise ratio.
