A gamma probe is a small, handheld device used to detect radiation in patients during surgery. It's primarily used to locate sentinel lymph nodes and parathyroid glands, but can also be used to detect tumors and other tissues. 
Gamma probes are used in a variety of procedures, including:
Sentinel lymph node mapping: A common use of gamma probes, this procedure helps determine if a tumor has spread to new locations. It's often used to stage breast cancer and melanoma.
Parathyroid surgery: Gamma probes can help locate parathyroid glands.
Tumor detection: Gamma probes can be used to detect cancerous tissue intraoperatively. 
Here are some features of gamma probes:
Directionality: Gamma probes are highly directional, which helps ensure accurate localization of targeted tissue. 
Radiation detectors: Gamma probes can use either scintillation or ionization detectors. 
Measurement units: Gamma probes can be calibrated in "ambient dose equivalent" units. 
Some gamma probe systems include:
TruNode™ Single-use Gamma Probe System: A fully sterile probe with a small tip and clear visual and audible user feedback. 
Neoprobe® Gamma Detection System: A Bluetooth probe system that offers high directionality and sensitivity. 
C-Trak Apollo: A wireless and wired gamma probe system. 
C-Trak Galaxy: A gamma probe system.