Head-to-head intra-individual comparison of total-body 2-[F]FDG PET/CT and digital PET/CT in patients with malignant tumor: how sensitive could it be?

Objectives: To comparatively evaluate the lesion-detecting ability of 2-[F]FDG total-body PET/CT (TB PET/CT) and conventional digital PET/CT.

Methods: This study enrolled 67 patients (median age, 65 years; 24 female and 43 male patients) who underwent a TB PET/CT scan and a conventional digital PET/CT scan after a single 2-[F]FDG injection (3.7 MBq/kg). Raw PET data for TB PET/CT were acquired over the course of 5 min, and images were reconstructed using data from the first 1, 2, 3, and 4 min and the entire 5 min (G1, G2, G3, G4, and G5, respectively). The conventional digital PET/CT scan acquired in 2-3 min per bed (G0). Two nuclear medicine physicians independently assessed subjective image quality using a 5-point Likert scale and recorded the number of 2-[F]FDG-avid lesions.

Results: A total of 241 lesions (69 primary lesions; 32 liver, lung, and peritoneum metastases; and 140 regional lymph nodes) among 67 patients with various types of cancer were analyzed. The subjective image quality score and SNR (signal-to-noise ratio) increased gradually from G1 to G5, and these values were significantly higher than the values at G0 (all p < 0.05). Compared to conventional PET/CT, G4 and G5 of TB PET/CT detected an additional 15 lesions (2 primary lesions; 5 liver, lung, and peritoneum lesions; and 8 lymph node metastases).

Conclusion: TB PET/CT was more sensitive than conventional whole-body PET/CT in detecting small (4.3 mm, maximum standardized uptake value (SUV) of 1.0) or low-uptake (tumor-to-liver ratio of 1.6, SUV of 4.1) lesions.

Clinical Relevance Statement: This study explored the gain of the image quality and lesion detectability of TB PET/CT, compared to conventional PET/CT, and recommended the appropriate acquisition time for TB PET/CT in clinical practice with an ordinary 2-[F] FDG dose.

Key Points: • TB PET/CT increases the effective sensitivity to approximately 40 times that of conventional PET scanners. • The subjective image quality score and signal-to-noise ratio of TB PET/CT from G1 to G5 were better than those of conventional PET/CT. • 2-[F]FDG TB PET/CT with a 4-min acquisition time at a regular tracer dose detected an additional 15 lesions compared to conventional PET/CT.