PET/CT (positron emission tomography and computed tomography) is an advanced imaging technique that combines the benefits of computed tomography (CT) and positron emission tomography (PET). CT provides detailed images of anatomical structure, while PET allows visualization of metabolic and functional activity in tissues, offering crucial information about the biochemical behavior of cells. This combination provides high-resolution images that integrate anatomical and functional data, making PET/CT particularly useful in the diagnosis and monitoring of oncological, cardiovascular, and neurological diseases. In oncology, for example, PET/CT is used to identify tumors, assess metastatic spread, monitor treatment response, and plan targeted therapies. PET uses radioisotopes that emit positrons through β+ decay. These positrons annihilate with electrons in the surrounding medium, producing two γ-rays of 511 keV emitted simultaneously in opposite directions. A series of time-coincident detectors around the patient determines their flight path. The process involves four key phases: positron emission, annihilation, γ-ray interaction with tissue, and detection. The PET acquisition system consists of ring detectors surrounding the patient, capturing γ-ray pairs emitted at a 180° angle. Modern PET systems use multiring detector arrays arranged in full rings with diameters of 80–90 cm. Tomographic imaging is achieved by recording lines of response (LORs) at various angles.