**7.5 Positron emission tomography (PET)**

PET has clearly defined roles in primary brain tumor imaging. The FDG uptake of high-grade gliomas is more as compared with low-grade or well-differentiated neoplasms, and FDG-PET can be useful in making a distinction between low- and high-grade gliomas [14].

A few limitations of FDG-PET as a cerebral imaging agent are that normal brain tissue has high physiologic glucose metabolic rate producing a high FDG uptake which may mask smaller lesions. Another issue is in the detection of tumors with only modest increases in glucose metabolism, such as low-grade tumors which may be difficult to interpret [15]. 18F-fluoroethyl-L-thyrosin (18F-FET) is a promising radiotracer in determining the grade of brain tumors.
