歯科放射線科医に必要なPET/CTの知識

抄録

Positron emission tomography （PET） is a functional imaging technique based on the detection of a short-lived radioactive tracer isotope. ［18F］ fluorodeoxyglucose （FDG）, which is the most commonly used radioactive tracer, is a glucose analog and so its concentration reflects the glucose metabolism rate within a tissue. As glucose metabolism is generally higher in malignant tumors than in normal tissue, FDG-PET is useful （and is widely used） for diagnosing malignant tumors. In this paper, we report the essentials of the FDG-PET-based diagnosis of primary tumors, nodal metastasis, tumor recurrence, and distant metastasis. Furthermore, we also discuss the pitfalls of this imaging technique.
FDG-PET can easily detect primary tumors because they usually exhibit marked FDG accumulation. However, it is not of great advantage for detecting oral cancers since most of them can be identified by clinical inspection. Although FDG-PET displays high diagnostic accuracy for nodal metastasis, inflammatory lymphadenopathy might sometimes produce false-positive results. Similarly, small metastatic lymph nodes and those containing necrosis can produce false-negative results. Concerning the evaluation of tumor recurrence, the diagnostic ability of FDG-PET might be superior to that of computed tomography （CT） and/or magnetic resonance imaging （MRI）. During the development of recurrent tumors, changes in glucose metabolism precede morphological changes, and thus, FDG-PET can detect recurrence earlier than CT or MRI. In addition, FDG-PET can provide whole-body images. Therefore, it can directly reveal distant metastasis and synchronous cancers.
In conclusion, it is essential to know the advantages and pitfalls of FDG-PET. Although it has some limitations, FDG-PET is a very useful imaging technique for managing patients with malignant tumors of the head and neck.