Positron Emission Tomography (PET) scanners are advanced nuclear medicine imaging systems that utilize positron-emitting radiotracers, such as Fluorine-18 FDG, to visualize metabolic activity at the molecular level with exceptional sensitivity. Integrated with CT or MRI for precise anatomical correlation (PET/CT), they excel in oncology for tumor detection, staging, treatment response monitoring, and identifying metastases in cancers like lung, lymphoma, and colorectal. Cardiac applications assess myocardial viability and perfusion, while neurological uses diagnose dementia, epilepsy, and brain tumors by mapping glucose uptake, blood flow, and receptor binding. High-resolution detectors and quantitative SUV metrics enable early disease detection, personalized therapy planning, and reduced radiation exposure, revolutionizing non-invasive diagnostics.