Reproducibility of Standardized Uptake Values Including Volume Metrics Between TOF-PET-MR and TOF-PET-CT.

Area of Science:

• Nuclear Medicine
• Radiology
• Oncology

Background:

• Reproducibility of quantitative measurements in Positron Emission Tomography (PET) is crucial for accurate oncologic staging and treatment response assessment.
• Time-of-flight (TOF) imaging improves signal-to-noise ratio in PET, enhancing lesion detectability and quantification.
• Comparing TOF-PET-CT and TOF-PET-MR is essential to understand potential differences in quantitative metrics.

Purpose of the Study:

• To investigate the reproducibility of tracer uptake measurements and volume metrics, including metabolic tumor volume (MTV) and tumor lesion glycolysis (TLG).
• To compare quantitative measurements obtained from time-of-flight PET-CT (TOF-PET-CT) and time-of-flight PET-MR (TOF-PET-MR) in oncologic patients.

Main Methods:

• Eighty patients with oncologic diagnoses underwent same-day TOF-PET-CT and TOF-PET-MR after a single 18F-FDG injection.
• Liver regions were assessed using a 30 mm spherical volume of interest (VOI) for Standardized Uptake Value (SUV) and Standardized Uptake Value Lean Body Mass (SUL) measurements.
• Tumor lesions were delineated using 40% and 50% SUVmax thresholds (VOI40, VOI50) to calculate SUVmax, SUVmean, SUVpeak, MTV, and TLG.

Main Results:

• No statistical difference was observed in liver SUV/SUL metrics between scanners.
• Tumor lesions showed significantly underestimated SUVmax, SUVmean, and SUVpeak on TOF-PET-MR compared to TOF-PET-CT (p < 0.001).
• Volume metrics (MTV, TLG) demonstrated strong correlations between TOF-PET-CT and TOF-PET-MR, with only TLG on VOI50 showing a statistical difference (p = 0.03).

Conclusions:

• PET metrics derived from TOF-PET-MR show good correlation with TOF-PET-CT.
• While SUVmax and SUVpeak are underestimated on TOF-PET-MR, MTV calculated using percentage thresholds can be considered equivalent between TOF-PET-CT and TOF-PET-MR.