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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.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.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).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.• 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.

Background Despite an increasing number of O-(2-18F-fluoroethyl)-L-tyrosine (18F-FET) PET studies in supratentorial gliomas, studies regarding the usefulness of 18F-FET PET in brainstem and spinal cord gliomas to date remain scarce. Methods Thirty-six 18F-FET PET scans were performed in 29 patients with brainstem (n = 29 scans) or spinal cord glioma (n = 7 scans). In 32 of 36 PET scans, a dynamic acquisition was performed. Fifteen scans in 15 patients were performed to assess newly diagnosed lesions, and 21 scans were obtained during follow-up: for diagnosing tumor progression (n = 15 scans in 14 patients) as well as for treatment monitoring (n = 6 scans in 3 patients). Four patients underwent additional serial scans (range, 1-2), and 3 of these 4 patients were examined for more than one indication. Maximum and mean tumor/brain ratios (TBRmax/mean) of 18F-FET uptake (20-40 min post injection) as well as kinetic 18F-FET uptake parameters were determined. Final diagnoses were confirmed histologically (54%) or by clinical follow-up (46%). Results In all newly diagnosed high-grade (n = 3 patients) and in 5 of 11 patients with low-grade gliomas, 18F-FET uptake was increased (TBRmax ≥2.5 and/or TBRmean ≥1.9). In 2 patients with newly diagnosed gliomas without MR contrast enhancement, 18F-FET PET nevertheless showed increased metabolism. At suspected progression, the combination of TBRs with kinetic 18F-FET parameters correctly identified presence or absence of progressive disease in 9 of 11 patients (82%). Conclusions This preliminary study suggests that 18F-FET PET adds valuable diagnostic information in brainstem and spinal cord glioma, particularly when the diagnostic information derived from MRI is equivocal.

BACKGROUND: The aim of this study was to investigate the potential of dynamic O-(2-[(18)F]fluoroethyl)-L-tyrosine ((18)F-FET) PET for differentiating local recurrent brain metastasis from radiation injury after radiotherapy since contrast-enhanced MRI often remains inconclusive.METHODS: Sixty-two patients (mean age, 55 ± 11 y) with single or multiple contrast-enhancing brain lesions (n = 76) on MRI after radiotherapy of brain metastases (predominantly stereotactic radiosurgery) were investigated with dynamic (18)F-FET PET. Maximum and mean tumor-to-brain ratios (TBRmax, TBRmean) of (18)F-FET uptake were determined (20-40 min postinjection) as well as tracer uptake kinetics (ie, time-to-peak and slope of time-activity curves). Diagnoses were confirmed histologically (34%; 26 lesions in 25 patients) or by clinical follow-up (66%; 50 lesions in 37 patients). Diagnostic accuracies of PET parameters for the correct identification of recurrent brain metastasis were evaluated by receiver-operating-characteristic analyses or the chi-square test.RESULTS: TBRs were significantly higher in recurrent metastases (n = 36) than in radiation injuries (n = 40) (TBRmax 3.3 ± 1.0 vs 2.2 ± 0.4, P < .001; TBRmean 2.2 ± 0.4 vs 1.7 ± 0.3, P < .001). The highest accuracy (88%) for diagnosing local recurrent metastasis could be obtained with TBRs in combination with the slope of time-activity curves (P < .001).CONCLUSIONS: The results of this study confirm previous preliminary observations that the combined evaluation of the TBRs of (18)F-FET uptake and the slope of time-activity curves can differentiate local brain metastasis recurrence from radiation-induced changes with high accuracy. (18)F-FET PET may thus contribute significantly to the management of patients with brain metastases.