Why is Gamma camera used in nuclear medicine?

A gamma camera is an instrument used to image radioactive emissions from a subject after injecting them with a radioactive drug which releases gamma rays. Planar imaging and SPECT uses gamma cameras. Function of gamma camera is to detect gamma radiation from the radionuclides introduced into the patient's body and to pinpoint the point of origin of radiation in the body. Gamma radiation is detected using scintillating crystal such as sodium iodide and photomultiplier tubes. To determine the direction of origin of radiation, lead collimeters are used. These collimeters ensure that only radiation coming from a narrow angular range will get through each gap in the lead, thus determining the direction to the source of the radiation. Ref: Nuclear Medicine Imaging: An Encyclopedic Dictionary By Joseph A. Thie, Page 53; Introduction to Biological Physics for the Health and Life Sciences By Kirsten Franklin, Page 404