Abstract
Purpose
To explore the feasibility of reducing administered tracer activities and to assess optimal activities for combined 18F-FDG-PET/MRI in pediatric oncology.
Methods
30 18F-FDG-PET/MRI examinations were performed on 24 patients with known or suspected solid tumors (10 girls, 14 boys, age 12 ± 5.6 [1–18] years; PET scan duration: 4 min per bed position). Low-activity PET images were retrospectively simulated from the originally acquired data sets using randomized undersampling of list mode data. PET data of different simulated administered activities (0.25–2.5 MBq/kg body weight) were reconstructed with or without point spread function (PSF) modeling. Mean and maximum standardized uptake values (SUVmean and SUVmax) as well as SUV variation (SUVvar) were measured in physiologic organs and focal FDG-avid lesions. Detectability of organ structures and of focal 18F-FDG-avid lesions as well as the occurrence of false-positive PET lesions were assessed at different simulated tracer activities.
Results
Subjective image quality steadily declined with decreasing tracer activities. Compared to the originally acquired data sets, mean relative deviations of SUVmean and SUVmax were below 5 % at 18F-FDG activities of 1.5 MBq/kg or higher. Over 95 % of anatomic structures and all pathologic focal lesions were detectable at 1.5 MBq/kg 18F-FDG. Detectability of anatomic structures and focal lesions was significantly improved using PSF. No false-positive focal lesions were observed at tracer activities of 1 MBq/kg 18F-FDG or higher. Administration of 18F-FDG activities of 1.5 MBq/kg is, thus, feasible without obvious diagnostic shortcomings, which is equivalent to a dose reduction of more than 50 % compared to current recommendations.
Conclusion
Significant reduction in administered 18F-FDG tracer activities is feasible in pediatric oncologic PET/MRI. Appropriate activities of 18F-FDG or other tracers for specific clinical questions have to be further established in selected patient populations.
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Funding
This study was partially funded as a cooperation project with Siemens Healthcare (Erlangen, Germany).
Ethical approval
All procedures performed in studies involving human participants were in accordance with the ethical standards of the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. This study was performed retrospectively on existing clinical imaging data. All legal guardians had given their written informed consent for the scientific analysis of acquired imaging data. Due to the retrospective nature of this study, formal approval was waived by the local ethics committee.
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Supplementary Figure 1
2-year-old girl with metastatic teratoma. Series of simulated low-dose PET images (0.25–2.5 MBq/kg 18 F-FDG) and the originally acquired image reconstructed using PSF. The solitary pleural metastasis (arrow) is visible in all data sets. Delineation of anatomic details (e.g. thymus or bowel) steadily improves with increasing tracer activities. (BMP 15795 kb)
Supplementary Figure 2
16-year-old boy with Hodgkin’s lymphoma. Series of simulated low-dose PET images (0.25, 0.5, 1 and 1.5 MBq/kg 18 F-FDG) and the originally acquired image reconstructed using PSF. Lymph node involvement (arrows) and sacral bone marrow involvement (circle) become better detectable with increasing tracer activities. All lesions are detectable at 1.5 MBq/kg. (BMP 18646 kb)
Supplementary Figure 3
7-year-old girl with non-Hodgkin’s lymphoma. Comparison of PET images without (left) and with (right) PSF reconstruction at a simulated tracer activity of 1 MBq/kg. The use of PSF reconstruction results in a better general image quality and better delineation of the FDG-avid mass of the neck (arrow). (BMP 5303 kb)
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Gatidis, S., Schmidt, H., la Fougère, C. et al. Defining optimal tracer activities in pediatric oncologic whole-body 18F-FDG-PET/MRI. Eur J Nucl Med Mol Imaging 43, 2283–2289 (2016). https://doi.org/10.1007/s00259-016-3503-5
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DOI: https://doi.org/10.1007/s00259-016-3503-5