F-GE-180 PET provides a remarkably high tumour-to-background contrast in untreated and pretreated glioblastoma and shows tracer uptake even beyond contrast enhancement on MRI. To what extent F-GE-180 uptake reflects the tumour extent of human gliomas and inflammatory cells remains to be evaluated in future prospective studies with guided stereotactic biopsies and correlation of histopathological results.

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BackgroundPET ligands targeting the translocator protein (TSPO) represent promising tools to visualise neuroinflammation. Here, we analysed parameters obtained in dynamic and static PET images using the novel TSPO ligand [18F]GE-180 in patients with relapsing remitting multiple sclerosis (RRMS) and an approach for semi-quantitative assessment of this disease in clinical routine.Seventeen dynamic [18F]GE-180 PET scans of RRMS patients were evaluated (90 min). A pseudo-reference region (PRR) was defined after identification of the least disease-affected brain area by voxel-based comparison with six healthy controls (HC) and upon exclusion of voxels suspected of being affected in static 60–90 min p.i. images. Standardised uptake value ratios (SUVR) obtained from static images normalised to PRR were correlated to the distribution volume ratios (DVR) derived from dynamic data with Logan reference tissue model.ResultsGroup comparison with HC revealed white matter and thalamus as most affected regions. Fewest differences were found in grey matter, and normalisation to frontal cortex (FC) yielded the greatest reduction in variability of healthy grey and white matter. Hence, FC corrected for affected voxels was chosen as PRR, leading to time-activity curves of FC which were congruent to HC data (SUV60–90 0.37, U test P = 0.42). SUVR showed a very strong correlation with DVR (Pearson ρ > 0.9). Focal MS lesions exhibited a high SUVR (range, 1.3–3.2).ConclusionsThis comparison with parameters from dynamic data suggests that SUVR normalised to corrected frontal cortex as PRR is suitable for the quantification of [18F]GE-180 uptake in lesions and different brain regions of RRMS patients. This efficient diagnostic protocol based on static [18F]GE-180 PET scans acquired 60–90 min p.i. allows the semi-quantitative assessment of neuroinflammation in RRMS patients in clinical routine.

[F]GE-180 PET can detect areas of focal macrophage/microglia activation in patients with RRMS in lesions with and without CE on MRI. Therefore, [F]GE-180 PET imaging is a sensitive and quantitative approach to the detection of active MS lesions. It may provide information beyond contrast-enhanced MRI and is readily applicable to all patients. [F]GE-180 PET imaging is therefore a promising new tool for the assessment of focal inflammatory activity in MS.

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