CT is an electronic computed tomography technique, which is a means of examination and can basically see anatomical structures; SPECT is single photon emission computed tomography, which is a gamma-ray imaging of tracers emitted from the patient’s body; MRI is magnetic resonance imaging, which uses magnetic resonance phenomena to reconstruct human structures and has advantages over CT in the nervous system, liver and joints; PET is positron emission computed tomography. PET is positron emission tomography, which is a more advanced imaging technology for clinical examination in the field of nuclear medicine. PET-CT is positron emission computed tomography, which is a fusion of PET and CT, and has more information than PET plus CT. It is a very advanced technology in the field of nuclear medicine, and is mostly used in the early diagnosis of tumors and definite clinical diagnosis. Briefly, CT and MRI belong to radiology department, while the latter SPECT and PET belong to nuclear medicine department.