Assessment of Brain Tumour Perfusion Using Early-Phase F-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-F-fluoroethyl)-L-tyrosine (F-FET).

PROCEDURE

Using a hybrid brain PET/MRI scanner, PWI and dynamic F-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 F-FET PET. For each patient, maps of MR-rCBV, early F-FET PET (0-2 min p.i.) and late F-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 F-FET maps (F-FET-rCBV) for concordance in signal intensity, tumour extent and intratumoural distribution.

RESULTS

TBRs calculated from MR-rCBV and F-FET-rCBV showed a significant correlation (r = 0.89, p < 0.001), while there was no correlation between late F-FET PET and MR-rCBV (r = 0.24, p = 0.16) and F-FET-rCBV (r = 0.27, p = 0.11). Visual rating yielded widely agreeing findings or only minor differences between MR-rCBV maps and F-FET-rCBV maps in 93 % of the tumours (range of three independent raters 91-94%, kappa among raters 0.78-1.0).

CONCLUSION

Early F-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 F-FET-rCBV provides the same clinical information as MR-rCBV.