Gamma camera in Nuclear Medicine is used for –
A gamma camera is a camera that records the distribution of a radioactive chemical that is taken up by a specific organ or tissue of interest. Nuclear medicine studies require the oral or intravenous introduction of very low - level radioactive chemicals (called radionuclides, radiopharmaceuticals or radiotracers) into the body. 
The radionuclides are taken up by the organs in the body and then emit faint gamma-ray signals, which are measured by a gamma camera.
Organ imaging
Measuring the radioactivity
Monitoring the surface contamination
RIA