Dual-time-point O-(2-[(18)F]fluoroethyl)-L-tyrosine PET for grading of cerebral gliomas.

OBJECTIVE: We aimed to evaluate the diagnostic potential of dual-time-point imaging with positron emission tomography (PET) using O-(2-[(18)F]fluoroethyl)-L-tyrosine ((18)F-FET) for non-invasive grading of cerebral gliomas compared with a dynamic approach. METHODS: Thirty-six patients with histologically confirmed cerebral gliomas (21 primary, 15 recurrent; 24 high-grade, 12 low-grade) underwent dynamic PET from 0 to 50 min post-injection (p.i.) of (18)F-FET, and additionally from 70 to 90 min p.i. Mean tumour-to-brain ratios (TBRmean) of (18)F-FET uptake were determined in early (20-40 min p.i.) and late (70-90 min p.i.) examinations. Time-activity curves (TAC) of the tumours from 0 to 50 min after injection were assigned to different patterns. The diagnostic accuracy of changes of (18)F-FET uptake between early and late examinations for tumour grading was compared to that of curve pattern analysis from 0 to 50 min p.i. of (18)F-FET. RESULTS: The diagnostic accuracy of changes of the TBRmean of (18)F-FET PET uptake between early and late examinations for the identification of HGG was 81% (sensitivity 83%; specificity 75%; cutoff - 8%; p < 0.001), and 83% for curve pattern analysis (sensitivity 88%; specificity 75%; p < 0.001). CONCLUSION: Dual-time-point imaging of (18)F-FET uptake in gliomas achieves diagnostic accuracy for tumour grading that is similar to the more time-consuming dynamic data acquisition protocol. KEY POINTS: • Dual-time-point imaging is equivalent to dynamic FET PET for grading of gliomas. • Dual-time-point imaging is less time consuming than dynamic FET PET. • Costs can be reduced due to higher patient throughput. • Reduced imaging time increases patient comfort and sedation might be avoided. • Quicker image interpretation is possible, as no curve evaluation is necessary.

Comparison of (18)F-FET PET and 5-ALA fluorescence in cerebral gliomas.

PURPOSE: The aim of the study was to compare presurgical (18)F-fluoroethyl-L: -tyrosine ((18)F-FET) uptake and Gd-diethylenetriaminepentaacetic acid (DTPA) enhancement on MRI (Gd) with intraoperative 5-aminolevulinic acid (5-ALA) fluorescence in cerebral gliomas. METHODS: (18)F-FET positron emission tomography (PET) was performed in 30 patients with brain lesions suggestive of diffuse WHO grade II or III gliomas on MRI. PET and MRI data were coregistered to guide neuronavigated biopsies before resection. After oral application of 5-ALA, 38 neuronavigated biopsies were taken from predefined tumour areas that were positive or negative for (18)F-FET or Gd and checked for 5-ALA fluorescence. (18)F-FET uptake with a mean tumour to brain ratio ≥1.6 was rated as positive. RESULTS: Of 38 biopsies, 21 corresponded to high-grade glioma tissue (HGG) of WHO grade III (n = 19) or IV (n = 2) and 17 biopsies to low-grade glioma tissue (LGG) of WHO grade II. In biopsies corresponding to HGG, (18)F-FET PET was positive in 86% (18/21), but 5-ALA and Gd in only 57% (12/21). A mismatch between Gd and 5-ALA was observed in 6 of 21 cases of HGG biopsy samples (3 Gd-positive/5-ALA-negative and 3 Gd-negative/5-ALA-positive). In biopsies corresponding to LGG, (18)F-FET was positive in 41% (7/17), while 5-ALA and Gd were negative in all but one instance. All tumour areas with 5-ALA fluorescence were positive on (18)F-FET PET. CONCLUSION: There are differences between (18)F-FET and 5-ALA uptake in cerebral gliomas owing to a limited sensitivity of 5-ALA to detect tumour tissue especially in LGG. (18)F-FET PET is more sensitive to detect glioma tissue than 5-ALA fluorescence and should be considered as an additional tool in resection planning.

Differential uptake of O-(2-18F-fluoroethyl)-L-tyrosine, L-3H-methionine, and 3H-deoxyglucose in brain abscesses.

UNLABELLED: The amino acid O-(2-(18)F-fluoroethyl)-L-tyrosine ((18)F-FET) has been shown to be a useful tracer for brain tumor imaging. Experimental studies demonstrated no uptake of (18)F-FET in inflammatory cells but increased uptake has been reported in single cases of human brain abscesses. To explore this inconsistency, we investigated the uptake of (18)F-FET in comparison with that of L-[methyl-(3)H]methionine ((3)H-MET) and D-(3)H-deoxyglucose ((3)H-DG) in brain and calf abscesses in rats. METHODS: Abscesses were induced in the brain (n = 9) and calf (n = 5) of Fisher CDF rats after inoculation of Staphylococcus aureus. Five days later, (18)F-FET and (3)H-MET (n = 10) or (18)F-FET and (3)H-DG (n = 4) were injected intravenously. One hour after injection the rats were sacrificed, and the brain or calf muscle was investigated using dual-tracer autoradiography. Lesion-to-background ratios (L/B) and standardized uptake values (SUVs) were calculated. The autoradiograms were compared with histology and immunostaining for glial fibrillary acidic protein (GFAP), CD68 for macrophages, and CD11b for microglia. RESULTS: (18)F-FET uptake in the area of macrophage infiltration and activated microglia at the rim of the brain abscesses was low (L/B, 1.5 +/- 0.4). In contrast, high uptake was observed for (3)H-MET as well as for (3)H-DG (L/B, 4.1 +/- 1.1 for (3)H-MET vs. 3.1 +/- 1.5 for (3)H-DG; P < 0.01 vs. (18)F-FET). Results for calf abscesses were similar. In the vicinity of the brain abscesses, slightly increased uptake was noted for (18)F-FET (L/B, 1.8 +/- 0.3) and (3)H-MET (L/B, 1.8 +/- 0.4), whereas (3)H-DG distribution was normal (L/B, 1.2 +/- 0.2). Anti-GFAP immunofluorescence showed a diffuse astrocytosis in those areas. CONCLUSION: Our results demonstrate that there is no accumulation of (18)F-FET in macrophages and activated microglia in experimental brain abscesses, whereas (3)H-MET and (3)H-DG exhibit high uptake in these cells. Thus, the specificity of (18)F-FET for gliomas may be superior to that (3)H-MET and (3)H-DG. Increased (18)F-FET uptake in human brain abscesses appears to be related to reactive astrocytosis.