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Point Spread Function Reconstruction for Integrated 18F-FET PET/MRI in Patients With Glioma

Does It Affect SUVs and Respective Tumor-to-Background Ratios?

Rogasch, Julian Manuel Michael, MD*; Albers, Josefine, MD*; Steinkrüger, Ferdinand L., MD*; Lukas, Mathias, MSc*†; Wedel, Florian, MD*; Amthauer, Holger, MD*; Furth, Christian, MD*

doi: 10.1097/RLU.0000000000002423
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Purpose Semiquantitative 18F-FET PET assessment using the tumor's SUV or tumor-to-background ratios (TBRs) can separate gliomas from peritumoral tissue or progression from pseudoprogression. This study investigated if point spread function (PSF) reconstruction of 18F-FET PET data affects SUV-based dignity assessment.

Materials and Methods This study is a retrospective analysis of 87 glioma patients (female, 36; male, 51; age, 48 [13–81] years) undergoing 18F-FET PET/MRI for staging (n = 17) or restaging (n = 70). PET was reconstructed using ordered-subset expectation maximization with and without PSF. Lesions were delineated with semiautomated background-adapted thresholding relative to SUVmax; background was delineated contralaterally. Comparative measurements with a National Electrical Manufacturers Association International Electrotechnical Commission PET body phantom (sphere-to-background ratios, 8:1 and 4:1) were performed.

Results PSF showed significantly higher tumor SUVmax (median difference, +0.1; interquartile range, 0.04–0.18), SUVmean (+0.05; 0.03–0.08), TBRmax|mean (+0.1; 0.04–0.2), and TBRmean|mean (+0.06; 0.03–0.09) than non-PSF (P < 0.001). Background SUVmean was unaffected. In patients and phantom, differences between PSF and non-PSF increased with TBR and decreased with lesion's PET volume. Differences only exceeded 0.2 SUV for SUVmax or 0.1 SUV for SUVmean if TBR was greater than 3 and lesion's PET volume was less than 10 mL (d = 27 mm). Dignity assessment by PSF and non-PSF was concordant in all patients examined for staging (cutoff, TBRmean|mean > 1.6; positive, 14; negative, 3) and restaging (cutoff, TBRmax|mean > 2.0; positive, 67; negative, 3).

Conclusions PSF increased tumor SUVmax and SUVmean compared with non-PSF 18F-FET PET/MRI data, especially in small lesions with high TBR (>3). However, dignity assessment using established TBR cutoffs was not affected.

From the *Department of Nuclear Medicine, Charité - Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health; and

Siemens Healthcare GmbH, Berlin, Germany.

Received for publication October 9, 2018; revision accepted October 31, 2018.

Conflicts of interest and sources of funding: M.L. is an employee of Siemens Healthcare GmbH. All other authors state that there is no conflict of interest.

J.M.M.R. and J.A. share the first authorship.

Correspondence to: Julian Manuel Michael Rogasch, MD, Department of Nuclear Medicine, Charité–Universitätsmedizin Berlin, Augustenburger Platz 1, D-13353 Berlin, Germany. E-mail: julian.rogasch@charite.de.

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