正子斷層掃描 (PET) 是較新的生理功能及代謝性的影像。雖然儀器與檢查時所使用的放射性藥物很昂貴，經過十多年的臨床應用，目前已經證實它對於癌症的診斷與評估癌症的生理病理有絕對的價值，尤其是肺癌、乳癌、大腸癌、頭頸部癌、食道癌、子宮頸癌、惡性淋巴瘤、黑色素細胞癌及復發的甲狀腺癌。PET在腫瘤的應用包括：(1) 正確的診斷癌症及復發時的偵測，早期診斷可避免重複使用其他診斷影像，在癌細胞散佈前以予摘除。(2) 正確的決定癌症分期，以利選擇適當的治療方法。(3) 評估癌症治療的療效，PET 檢查可以告知治療後腫瘤仍存活或已壞死，對於腫瘤周圍水腫及瘢痕組織也可做鑑別診斷。(4) 評估惡性腫瘤的預後。PET 與 X 光電腦斷層掃描 (CT) 結合的儀器稱 PET/CT，可以更精確地定位病灶的解剖結構位置。與磁振造影 (MRI) 結合的儀器 PET/MRI 也正研發中。將來以正子同位素結合研發中的各種生物標記、新藥、受體、血管新生、細胞凋零、基因探針、幹細胞等做 PET 造影，將會帶入生物醫學的新
紀元。

Positron emission tomography is a relatively new well-known imaging modality in medicine. A glucose analog,fluorine-18 fluorodeoxyglucose (18F-FDG, FDG), may accumulate within cells and is proportional to the rate of glucose transport and metabolism. Using FDG as a radiotracer, FDG-PET has high sensitivity and specificity for malignant tumor detection and assessment of the pathophysiology of the tumor. Clinical usefulness of FDG-PET include: (1) early detect and diagnose malignant tumor to avoid repeatedly using other diagnosing modalities (2)accurately stage and restage malignant disease (3) evaluate the effects of certain type of therapy (4) early assess the prognosis of malignant tumor. Images obtained with a combined PET and CT (PET/CT), PET and MRI (PET/MRI)
scanner can depict exact anatomic landmarks, enable precise localization of metabolic abnormalities, and correctly identify physiologic, nonspecific uptake that would otherwise be mistaken for a malignant tumor. In the future,labeling of positron emitted isotope with developing biomarker, receptor, gene probe, stem cell, and drug for PETmay reach a novel medical era.