Early static ^sup 18^F-FET-PET scans have a higher accuracy for glioma grading than the standard 20-40 min scans

Purpose Current guidelines for glioma imaging by positron emission tomography (PET) using the amino acid analogue O-(2-[^sup 18^F]fluoroethyl)-L-tyrosine (^sup 18^F-FET) recommend image acquisition from 20-40 min post injection (p.i.). The maximal tumour-to-background evaluation (TBR^sub max^) obtained in these summation images does not enable reliable differentiation between low and high grade glioma (LGG and HGG), which, however, can be achieved by dynamic ^sup 18^F-FET-PET. We investigated the accuracy of tumour grading using TBR^sub max^ values at different earlier time points after tracer injection. Methods Three hundred and fourteen patients with histologically proven primary diagnosis of glioma (131 LGG, 183 HGG) who had undergone 40-min dynamic ^sup 18^F-FET-PET scans were retrospectively evaluated. TBR^sub max^ was assessed in the standard 20-40 min summation images, as well as in summation images from 0-10 min, 5-15 min, 5-20 min, and 15-30 min p.i., and kinetic analysis was performed. TBR^sub max^ values and kinetic analysis were correlated with histological classification. ROC analyses were performed for each time frame and sensitivity, specificity, and accuracy were assessed. Results TBR^sub max^ values in the earlier summation images were significantly better for tumour grading (P