Assessment of brain tumour perfusion using early-phase 18F-FET -PET: comparison with perfusion-weighted MRI

Abstract Background: Morphological imaging using MRI is essential for brain tumour diagnostics. Dynamic susceptibility contrast (DSC) perfusion-weighted MRI (PWI), as well as amino acid PET, may provide additional information in ambiguous cases. Since PWI is not always performed as part of standard MRI in brain tumours, we explored whether maps of relative cerebral blood volume (rCBV) in brain tumours can be extracted from the early phase of PET using O-(2-18F-fluoroethyl)-L-tyrosine (18F-FET). Using a hybrid BrainPET/MRI scanner, PWI and dynamic 18F-FET PET were performed in 33 patients with cerebral glioma and in four patients with highly vascularized meningiomas. Based on the dynamic PET data in meningiomas, the time interval from 0 – 2 min p.i. was selected to best reflect the blood pool phase in 18F-FET PET. For each patient, maps of MR-rCBV, early 18F-FET PET (0-2 min p.i.) and late 18F-FET PET (20-40 min p.i.) were generated and coregistered. Volumes of interest were placed on the tumour (VOI-TU) and on the normal-appearing contralateral brain tissue (VOI-REF). The correlation between the tumour-to-brain ratios (TBR) of the different parameters was analyzsed. In addition, three independent observers evaluated the MR-rCBV and early 18F-FET maps (18F-FET-rCBV) for concordance in signal intensity, tumour extent and intratumoural distribution. Results: TBRs calculated from MR-rCBV and 18F-FET-rCBV showed a significant correlation (r = 0.89, p < 0.001), while there was no correlation between late 18F-FET PET and MR-rCBV (r = 0.24, p = 0.16) or 18F-FET-rCBV (r = 0.27, p = 0.11). Visual rating yielded widely agreeing findings or only minor differences between the MR-rCBV maps and 18F-FET-rCBV maps in 93 % of the tumours (range of three independent raters 91–94%, kappa among raters 0.78-1.0). Conclusion: Early 18F-FET-maps (0-2min p.i.) in gliomas provide similar information to MR-rCBV maps and may be helpful when PWI is not possible or available. Further studies in recurrent gliomas are needed to evaluate whether 18F-FET-rCBV provides the same clinical information as MR-rCBV.