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. 2025 Feb 5;12(1):13.
doi: 10.1186/s40658-025-00720-z.

Low-activity [18F]-somatostatin receptor (SSTR) imaging using [18F]SiTATE on a long axial field-of-view PET/CT scanner

Nils F Trautwein  1   2 , Eduardo Calderón  3 , Pia M Linder  3 , Gerald Reischl  4   5 , Philippe Driessen  3 , Wenhong Lan  3 , Andreas S Brendlin  6 , Thorben Groß  7 , Helmut Dittmann  3   8 , Martina Hinterleitner  8   7   5 , Christian la Fougère  3   8   5   9 , Fabian P Schmidt  3   4 , Lena S Kiefer  3
Affiliations

Low-activity [18F]-somatostatin receptor (SSTR) imaging using [18F]SiTATE on a long axial field-of-view PET/CT scanner

Nils F Trautwein et al. EJNMMI Phys. .

Abstract

Purpose: 18F-labelled somatostatin receptor tracers have recently gained popularity due to their better spatial resolution, longer half-life and lower costs compared to 68Ga-labeled tracers. The aim of this study was to evaluate the impact and limitations of reduced administered activities of [18F]SiTATE on image quality, lesion detectability and quantitative PET parameters in a long axial field-of-view (LAFOV) PET/CT scanner.

Methods: Twenty-four patients with histologically confirmed neuroendocrine tumor, who underwent clinically indicated [18F]SiTATE PET/CT examination (3.0 MBq/kg, 5 min PET scan time) on a Siemens Biograph Vision Quadra LAFOV PET/CT, were included retrospectively in this study. PET list-mode data were rebinned for shorter frame durations to simulate 5 min scans with lower activities of injected radiotracer. A comparison of image reconstruction in high sensitivity (HS) and ultra-high sensitivity mode (UHS) mode was performed. Subjective image quality, noise and lesion detectability of n = 122 lesions were rated using a 5-point Likert scale. The molecular tumor volume (MTV), signal-to-noise ratio (SNR), tumor-to-liver activity concentration ratio (TLR) and standardized uptake values (SUV) were analyzed.

Results: Subjective image quality decreased with simulated reduction of injected activity with generally superior ratings in the UHS mode compared to the HS mode. Despite a reduction to 1 MBq/kg of [18F]SiTATE all lesions were still detected while at 0.25 MBq/kg lesion detectability decreased to 70% (HS) and 93% (UHS). Only minor changes in SUVmean and TLR were detected with reduced activity. However, reduced activities led to an increase in SUVSD, which in turn caused a decrease in SNR (at 1 MBq/kg: 7.3 in HS and 9.0 in UHS mode and an increase in deviation of the MTV.

Conclusion: Reducing the administered activity of injected [18F]SiTATE by 66% to 1 MBq/kg (HS & UHS) is feasible in a LAFOV PET/CT scanner, maintaining clinically diagnostic image quality without statistically significant deviations in PET uptake parameters and MTV. Furthermore, in low activity [18F]SiTATE PET/CT, the UHS mode improves image quality and noise as well as lesion detectability compared to HS mode, further reinforcing the clinical benefits of this recently introduced reconstruction mode.

Keywords: LAFOV PET/CT; Low-activity [18F]SiTATE PET; Total-Body-PET; [18F]-SSTR imaging; [18F]SiTATE.

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Conflict of interest statement

Declarations. Ethical approval: The study was based on a prospective PET/CT registry and was retrospectively approved by the institutional Review Board of the University Hospital of Tuebingen (#167/2020BO2). The study was performed in accordance with the Declaration of Helsinki. Conflict of interest: N.T. reports fees from Novartis. Schmidt F. and la Fougère C. received a research grant from Siemens Healthineers. No other potential conflict of interest relevant to this article exist. The funders had no role in the design of the study; in the collection, analyses, or interpretation of the data; in the writing of the manuscript; or in the decision to publish the results.

Figures

Fig. 1
Fig. 1
Axial and coronal [18F]SiTATE PET of a 5 min scan in HS mode (A/C) and UHS mode (B/D) of a 78 years old female patient with a metastasized ileum NET G2. 1: 3.0 MBq/kg; 2: 2.0 MBq/kg; 3: 1.0 MBq/kg; 4: 0.5 MBq/kg; 5: 0.25 MBq/kg
Fig. 2
Fig. 2
Subjective image quality ratings according to Likert-Score. Overall image quality (A: HS; B: UHS), image noise (C: HS; D: UHS) and lesion conspicuity (E: HS; F: UHS)
Fig. 3
Fig. 3
SNR (A) and CoV (B) of the liver background according to simulated dose and sensitivity mode. All data are presented as boxplot showing the median value (central line) and the 25–75th percentiles. Whiskers represent the maximum and minimum and are considered as significant at p < 0.05 (*), p < 0.01 (**), p < 0.001 (***) and p < 0.0001 (****)
Fig. 4
Fig. 4
SUVmean (A), TLR (B) and SUVSD (C) values for all lesions. Percentage changes in the MTV in comparison to the standard scan with 3 MBq/kg in HS mode. All data are presented as boxplot showing the median value (central line) and the 25–75th percentiles. Whiskers represent the maximum and minimum and are considered as significant at p < 0.05 (*), p < 0.01 (**), p < 0.001 (***), p < 0.0001 (****) and as not significant (ns)
Fig. 5
Fig. 5
[18F]SiTATE PET reconstructions of a 5 min scan in HS mode (A in blue) and UHS mode (B in orange) of a 67 years old female patient with a hepatic and lymphogenic metastasized small intestine NET G2. With reduced injected activity, the decrease in the MTV can also be recognized, particularly in the area of the mesenteric lymph nodes (arrow). 1: 3.0 MBq/kg; 2: 2.0 MBq/kg; 3: 1.0 MBq/kg; 4: 0.5 MBq/kg; 5: 0.25 MBq/kg
Fig. 6
Fig. 6
A: Transaxial view of the central slice of the IEC Phantom with 18F activity concentrations equivalent to an injected activity of 0.5, 2.0 and 3.0 MBq/kg and a 5 min scan. Further, comparison of the standard setting with 4 iterations and 5 subsets (4i5s) in comparison to 3i5s and 2i5s; B: Contrast Recovery (CRC) determined for the 10-, 17- and 37-mm spheres of the IEC phantom as a function of the coefficient of variation (CoV). Values are reported for activity concentrations equivalent to the patient examinations (3.0, 2.0, 1.0, 0.5 and 0.25 MBq/kg) and iterations from 2i5s-5i5s. Each point represents one iteration setting with the number of iterations increasing from left to right
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