An intraoperative surgical probe using a mercuric iodide radiation detector is proposed. The probe will have the ability to simultaneously measure the 140 keV gamma-ray emission and the 18 keV x-ray emission from Tc-99m. Good energy resolution is necessary for the lower energy x-rays to separate them from the potentially large scatter background. Comparison of the measured strength of the x-ray and gamma ray transitions provides a sensitive indicator of the depth in soft tissue of the radioactive source. This adds to the capability of surgical probes by providing a third dimension of position sensitivity. Current state-of-the art probes do not provide accurate, if any source depth information. The surgeon can use this depth information to more accurately locate margins and metastases. An experimental evaluation of the detectors is proposed, leading to specification of how to configure detectors for this application and verification that the method is feasible.
