Comparison of ¹⁸F-FET PET and Perfusion-Weighted MR Imaging: A PET/MR Imaging Hybrid Study in Patients with Brain Tumors

Abstract

PET using O-(2-18 F-fluoroethyl)-L-tyrosine ( 18 F-FET) provides important diagnostic information in addition to that from conventional MR imaging on tumor extent and activity of cerebral gliomas. Recent studies suggest that perfusion-weighted MR imaging (PWI), especially maps of regional cerebral blood volume (rCBV), may provide similar diagnostic information. In this study, we directly compared 18 F-FET PET and PWI in patients with brain tumors. Methods: Fifty-six patients with gliomas were investigated using static 18 F-FET PET and PWI. For comparison, 8 patients with meningiomas were included. We generated a set of tumor and reference volumes of interest (VOIs) based on morphologic MR imaging and transferred these VOIs to the corresponding 18 F-FET PET scans and PWI maps. From these VOIs, tumor-to-brain ratios (TBR) were calculated, and normalized histograms were generated for 18 F-FET PET and rCBV maps. Furthermore, in rCBV maps and in 18 F-FET PET scans, tumor volumes, their spatial congruence, and the distance between the local hot spots were assessed. Results: For patients with glioma, TBR was significantly higher in 18 F-FET PET than in rCBV maps (TBR, 2.28 ± 0.99 vs. 1.62 ± 1.13; P , 0.001). Histogram analysis of the VOIs revealed that 18 F-FET scans could clearly separate tumor from background. In contrast, deriving this information from rCBV maps was difficult. Tumor volumes were significantly larger in 18 F-FET PET than in rCBV maps (tumor volume, 24.3 ± 26.5 cm 3 vs. 8.9 ± 13.9 cm 3 ; P , 0.001). Accordingly, spatial overlap of both imaging parameters was poor (congruence, 11.0%), and mean distance between the local hot spots was 25.4 ± 16.1 mm. In meningioma patients, TBR was higher in rCBV maps than in 18 F-FET PET (TBR , 5.33 ± 2.63 vs. 2.37 ± 0.32; P , 0.001) whereas tumor volumes were comparable. Conclusion: In patients with cerebral glioma, tumor imaging with 18 F-FET PET and rCBV yields different information. 18 F-FET PET shows considerably higher TBRs and larger tumor volumes than rCBV maps. The spatial congruence of both parameters is poor. The locations of the local hot spots differ considerably. Taken together, our data show that metabolically active tumor tissue of gliomas as depicted by amino acid PET is not reflected by rCBV as measured with PWI.

Epileptic Activity Increases Cerebral Amino Acid Transport Assessed by 18F-Fluoroethyl-l-Tyrosine Amino Acid PET: A Potential Brain Tumor Mimic

“…3) glucose metabolism. Similarly, previous studies have shown high 18 F-FET uptake in gliomas with low cerebral blood flow or blood volume (29,30). Therefore, it is unlikely that increased 18 F-FET uptake during seizure activity is caused by hyperperfusion to a major extent.…”

PET Imaging in Glioblastoma: Use in Clinical Practice

“…Furthermore, in a study of initial diagnosis of 56 gliomas, 24 of which were glioblastomas, 18 F-FET showed considerably higher TBRmax and larger tumor volumes when compared to regional cerebral blood volume maps derived from perfusion-weighted MR imaging (53). In addition, postoperative 18 F-FET PET has been shown to reveal residual tumor with higher sensitivity than MRI as well as show larger tumor volumes (54).…”

Amino acid PET in neuro-oncology: applications in the clinic

“…From the researcher's point of view, this technology provides the optimal requirements for comparative imaging studies using amino acid PET and advanced MRI, ideally with histological confirmation of imaging findings by stereotactic biopsy. However, the problem of MRI-based attenuation correction is currently not fully solved [24] and the clinical value of adding advanced MRI sequences in multiparametric imaging setting has to be confirmed in further studies [25,26].…”