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Contrast-enhanced MRI is the method of choice for brain tumor diagnostics, despite its low specificity for tumor tissue. This study compared the contribution of MR spectroscopic imaging (MRSI) and amino acid PET to improve the detection of tumor tissue. Methods: In 30 untreated patients with suspected glioma, O -(2-[ 18 F]fluoroethyl)-l-tyrosine ( 18 F-FET) PET; 3-T MRSI with a short echo time; and fluid-attenuated inversion recovery, T2-weighted, and contrast-enhanced T1-weighted MRI were performed for stereotactic biopsy planning. Serial samples were taken along the needle trajectory, and their masks were projected to the preoperative imaging data. Each sample was individually evaluated neuropathologically. 18 F-FET uptake and the MRSI signals choline (Cho), N -acetyl-aspartate (NAA), creatine, myoinositol, and derived ratios were evaluated for each sample and classified using logistic regression. The diagnostic accuracy was evaluated by receiver operating characteristic analysis. Results: On the basis of the neuropathologic evaluation of tissue from 88 stereotactic biopsies, supplemented with 18 F-FET PET and MRSI metrics from 20 areas on the healthy-appearing contralateral hemisphere to balance the glioma/nonglioma groups, 18 F-FET PET identified glioma with the highest accuracy (area under the receiver operating characteristic curve, 0.89; 95% CI, 0.81-0.93; threshold, 1.4 × background uptake). Among the MR spectroscopic metabolites, Cho/NAA normalized to normal brain tissue showed the highest diagnostic accuracy (area under the receiver operating characteristic curve, 0.81; 95% CI, 0.71-0.88; threshold, 2.2). The combination of 18 F-FET PET and normalized Cho/NAA did not improve the diagnostic performance. Conclusion: MRI-based delineation of gliomas should preferably be supplemented by 18 F-FET PET., (© 2024 by the Society of Nuclear Medicine and Molecular Imaging.)

We investigated the value of O -(2- 18 F-fluoroethyl)-l-tyrosine ( 18 F-FET) PET for treatment monitoring of immune checkpoint inhibition (ICI) or targeted therapy (TT) alone or in combination with radiotherapy in patients with brain metastasis (BM) since contrast-enhanced MRI often remains inconclusive. Methods: We retrospectively identified 40 patients with 107 BMs secondary to melanoma ( n = 29 with 75 BMs) or non-small cell lung cancer ( n = 11 with 32 BMs) treated with ICI or TT who had 18 F-FET PET ( n = 60 scans) for treatment monitoring from 2015 to 2019. Most patients ( n = 37; 92.5%) had radiotherapy during the course of the disease. In 27 patients, 18 F-FET PET was used to differentiate treatment-related changes from BM relapse after ICI or TT. In 13 patients, 18 F-FET PET was performed for response assessment to ICI or TT using baseline and follow-up scans (median time between scans, 4.2 mo). In all lesions, static and dynamic 18 F-FET PET parameters were obtained (i.e., mean tumor-to-brain ratios [TBR], time-to-peak values). Diagnostic accuracies of PET parameters were evaluated by receiver-operating-characteristic analyses using the clinical follow-up or neuropathologic findings as a reference. Results: A TBR threshold of 1.95 differentiated BM relapse from treatment-related changes with an accuracy of 85% ( P = 0.003). Metabolic responders to ICI or TT on 18 F-FET PET had a significantly longer stable follow-up (threshold of TBR reduction relative to baseline, ≥10%; accuracy, 82%; P = 0.004). Furthermore, at follow-up, time to peak in metabolic responders increased significantly ( P = 0.019). Conclusion: 18 F-FET PET may add valuable information for treatment monitoring in BM patients treated with ICI or TT., (© 2021 by the Society of Nuclear Medicine and Molecular Imaging.)

Unlabelled: In patients with low-grade glioma (LGG) of World Health Organization (WHO) grade II, early detection of progression to WHO grade III or IV is of high clinical importance because the initiation of a specific treatment depends mainly on the WHO grade. In a significant number of patients with LGG, however, information on tumor activity and malignant progression cannot be obtained on the basis of clinical or conventional MR imaging findings only. We here investigated the potential of O-(2-(18)F-fluoroethyl)-L-tyrosine ((18)F-FET) PET to noninvasively detect malignant progression in patients with LGG., Methods: Twenty-seven patients (mean age ± SD, 44 ± 15 y) with histologically proven LGG (WHO grade II) were investigated longitudinally twice using dynamic (18)F-FET PET and routine MR imaging. Initially, MR imaging and PET scans were performed, and diagnosis was confirmed on the basis of biopsy. Subsequently, PET scans were obtained when clinical findings or contrast-enhanced MR imaging suggested malignant progression. Maximum and mean tumor-to-brain ratios (20-40 min after injection) (TBRmax and TBRmean, respectively) of (18)F-FET uptake as well as tracer uptake kinetics (i.e., time to peak [TTP] and patterns of the time-activity curves) were determined. The diagnostic accuracy of imaging parameters for the detection of malignant progression was evaluated by receiver-operating-characteristic analyses and by Fisher exact test for 2 × 2 contingency tables., Results: In patients with histologically proven malignant progression toward WHO grade III or IV (n = 18), TBRmax and TBRmean increased significantly, compared with baseline (TBRmax, 3.8 ± 1.0 vs. 2.4 ± 1.0; TBRmean, 2.2 ± 0.3 vs. 1.6 ± 0.6; both P < 0.001), whereas TTP decreased significantly (median TTP, 35 vs. 23 min; P < 0.001). Furthermore, time-activity curve patterns changed significantly in 10 of 18 patients (P < 0.001). The combined analysis of (18)F-FET PET parameters (i.e., changes of TBRmax, TTP, or time-activity curve pattern) yielded a significantly higher diagnostic accuracy for the detection of malignant progression than changes of contrast enhancement in MR imaging (accuracy, 81% vs. 63%; P = 0.003)., Conclusion: Both tumor-to-brain ratio and kinetic parameters of (18)F-FET PET uptake provide valuable diagnostic information for the noninvasive detection of malignant progression of LGG. Thus, repeated (18)F-FET PET may be helpful for further treatment decisions.

Unlabelled: The aim of this study was to investigate the potential of O-(2-(18)F-fluoroethyl)-L-tyrosine ((18)F-FET) PET for differentiating local recurrent brain metastasis from radiation necrosis after radiation therapy because the use of contrast-enhanced MRI for this issue is often difficult., Methods: Thirty-one patients (mean age ± SD, 53 ± 11 y) with single or multiple contrast-enhancing brain lesions (n = 40) on MRI after radiation therapy of brain metastases were investigated with dynamic (18)F-FET PET. Maximum and mean tumor-to-brain ratios (TBR(max) and TBR(mean), respectively; 20-40 min after injection) of (18)F-FET uptake were determined. Time-activity curves were generated, and the time to peak (TTP) was calculated. Furthermore, time-activity curves of each lesion were assigned to one of the following curve patterns: (I) constantly increasing (18)F-FET uptake, (II) (18)F-FET uptake peaking early (TTP ≤ 20 min) followed by a plateau, and (III) (18)F-FET uptake peaking early (TTP ≤ 20 min) followed by a constant descent. The diagnostic accuracy of the TBR(max) and TBR(mean) of (18)F-FET uptake and the curve patterns for the correct identification of recurrent brain metastasis were evaluated by receiver-operating-characteristic analyses or Fisher exact test for 2 × 2 contingency tables using subsequent histologic analysis (11 lesions in 11 patients) or clinical course and MRI findings (29 lesions in 20 patients) as reference., Results: Both TBR(max) and TBR(mean) were significantly higher in patients with recurrent metastasis (n = 19) than in patients with radiation necrosis (n = 21) (TBR(max), 3.2 ± 0.9 vs. 2.3 ± 0.5, P < 0.001; TBR(mean), 2.1 ± 0.4 vs. 1.8 ± 0.2, P < 0.001). The diagnostic accuracy of (18)F-FET PET for the correct identification of recurrent brain metastases reached 78% using TBR(max) (area under the ROC curve [AUC], 0.822 ± 0.07; sensitivity, 79%; specificity, 76%; cutoff, 2.55; P = 0.001), 83% using TBR(mean) (AUC, 0.851 ± 0.07; sensitivity, 74%; specificity, 90%; cutoff, 1.95; P < 0.001), and 92% for curve patterns II and III versus curve pattern I (sensitivity, 84%; specificity, 100%; P < 0.0001). The highest accuracy (93%) to diagnose local recurrent metastasis was obtained when both a TBR(mean) greater than 1.9 and curve pattern II or III were present (AUC, 0.959 ± 0.03; sensitivity, 95%; specificity, 91%; P < 0.001)., Conclusion: Our findings suggest that the combined evaluation of the TBR(mean) of (18)F-FET uptake and the pattern of the time-activity curve can differentiate local brain metastasis recurrence from radionecrosis with high accuracy. (18)F-FET PET may thus contribute significantly to the management of patients with brain metastases.