Assessment of Brain Tumour Perfusion Using Early-Phase 18F-FET PET: Comparison with Perfusion-Weighted MRI

Purpose: 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 often unavailable in patients referred for amino acid PET, 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). Procedure: Using a hybrid brain PET/MRI scanner, PWI and dynamic ¹⁸F-FET PET were performed in 33 patients with cerebral glioma and four patients with highly vascularized meningioma. The time interval from 0 to 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 normal-appearing brain (VOI-REF). The correlation between tumour-to-brain ratios (TBR) of the different parameters was analysed. In addition, three independent observers evaluated 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) and ¹⁸F-FET-rCBV (r = 0.27, p = 0.11). Visual rating yielded widely agreeing findings or only minor differences between 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 (0–2 min 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 gliomas are needed to evaluate whether ¹⁸F-FET-rCBV provides the same clinical information as MR-rCBV.