A PET study of (18)FDG uptake in soft tissue masses

A study was performed with the aim of investigating some of the methodologi cal factors affecting the ability of quantitative 2-[F-18] -fluoro-2-deoxy- D-glucose (FDG) positron emission tomography to assess tumour malignancy. T wenty-nine patients with soft tissue masses were studied using a 6-hour sca nning protocol and various indices of glucose metabolism were compared with histological grade. Significant differences were observed in the time-acti vity response of benign and high-grade tumours. High-grade sarcomas were fo und to reach a peak activity concentration approximately 4 h after injectio n whereas benign lesions reached a maximum within 30 min. This translated t o improved differentiation between these two tumour types using a standard uptake value (SUV) derived from images acquired at later times. An SUV meas ured 4 h post-injection was found to be as useful an index of tumour malign ancy as the metabolic rate of FDG determined using either Patlak or non-lin ear regression techniques. Each of these indices had a sensitivity and spec ificity of 100% and 76% respectively for the discrimination of high-grade s arcomas from benign tumours.