Abstract
PurposeThe aim of this study was to derive reference values of 18F-fluoro-ethyl-L-tyrosine positron emission tomography (18F-FET-PET) uptake in normal brain and head structures to allow for differentiation from tumor tissue.Materials and methodsWe examined the datasets of 70 patients (median age 53 years, range 15–79), whose dynamic 18F-FET-PET was acquired between January 2016 and October 2017. Maximum standardized uptake value (SUVmax), target-to-background standardized uptake value ratio (TBR), and time activity curve (TAC) of the 18F-FET-PET were assessed in tumor tissue and in eight normal anatomic structures and compared using the t-test and Mann-Whitney U-test. Correlation analyses were performed using Pearson or Spearman coefficients, and comparisons between several variables with Pearson’s chi-squared tests and Kruskal-Wallis tests as well as the Benjamini-Hochberg correction.ResultsAll analyzed structures showed an 18F-FET uptake higher than background (threshold: TBR > 1.5). The venous sinuses and cranial muscles exhibited a TBR of 2.03±0.46 (confidence interval (CI) 1.92–2.14), higher than the uptake of caudate nucleus, pineal gland, putamen, and thalamus (TBR 1.42±0.17, CI 1.38–1.47). SUVmax, TBR, and TAC showed no difference in the analyzed structures between subjects with high-grade gliomas and subjects with low-grade gliomas, except the SUVmax of the pineal gland (t-tests of the pineal gland: SUVmax: p = 0.022; TBR: p = 0.411). No significant differences were found for gender and age.ConclusionNormal brain tissue demonstrates increased 18F-FET uptake compared to background tissue. Two distinct clusters have been identified, comprising venous structures and gray matter with a reference uptake of up to SUVmax of 2.99 and 2.33, respectively.
Highlights
Positron emission tomography (PET) using the radiotracer 18F-fluoro-ethyl-L-tyrosine (18F-FET), an amino acid analogue, is becoming increasingly relevant in the initial assessment of primary brain tumors, and for differentiating tumor recurrences from post-therapeutic changes [1, 2]
SUVmax, TBR, and time activity curve (TAC) showed no difference in the analyzed structures between subjects with high-grade gliomas and subjects with low-grade gliomas, except the SUVmax of the pineal gland (t-tests of the pineal gland: SUVmax: p = 0.022; TBR: p = 0.411)
No significant differences were found for gender and age
Summary
Positron emission tomography (PET) using the radiotracer 18F-fluoro-ethyl-L-tyrosine (18F-FET), an amino acid analogue, is becoming increasingly relevant in the initial assessment of primary brain tumors, and for differentiating tumor recurrences from post-therapeutic changes [1, 2]. Proton MR spectroscopy (MRS) has been shown to be of value for grading and therapy response assessment of supratentorial gliomas [8,9,10]. Methodical challenges such as high susceptibility to artifacts in tumors close to air-filled spaces, variable acquisition techniques, volume averaging caused by voxel size and deviations in the calculation of metabolite ratios have limited widespread clinical implementation of MRS [8, 11]. Several cut-off values of the target-to-background (TBR) ratio were established for this purpose [18, 19]. 18F-FET-PET uptake of inflammatory lesions appeared negligible in several studies, which is useful when MRI results are equivocal [20,21,22]
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