Feasibility of Acquisitions Using Total-Body PET/CT with an Ultra-Low 18F-FDG Activity

Abstract

The present study aimed to evaluate the feasibility of ultra-low ¹⁸F-FDG activity in total-body PET/CT oncologic studies. Methods: Thirty patients with cancer were enrolled prospectively and underwent a total-body PET/CT scan 60 min after injection of an ultra-low ¹⁸F-FDG activity (0.37 MBq/kg). Of the 30 enrolled patients, 11 were diagnosed with colorectal cancer (CRC). PET raw data were acquired within 15 min and reconstructed using data from the first 1, 2, 4, 8, and 10 min and the entire 15 min (G1, G2, G4, G8, G10, and G15, respectively). Image quality was qualitatively assessed twice by 2 readers using a 5-point Likert scale. The Cohen κ-test was used to investigate the intra- and interreader agreement. The SUV_max of lesions; the SUV_max, SUV_mean, and SD of the livers; the tumor-to-background ratio; and the signal-to-noise ratio were measured and compared. The acquisition time for a clinically acceptable image quality using an ultra-low-activity injection was determined. In a matched-pair study, 11 patients with CRC who received a full ¹⁸F-FDG activity (3.7 MBq/kg) with an acquisition time of 2 min were selected retrospectively by matching sex, height, weight, body mass index, glucose level, uptake time, and pathologic types with the 11 CRC subjects in the prospective study. Qualitative and quantitative analyses were performed and compared between the 11 patients with CRC in the ultra-low-activity group and their matched full-activity controls. Results: Qualitative analysis of image quality showed good intra- and interreader agreements (all κ > 0.7). All the images acquired for 8 min or longer scored over 3 (indicating clinical acceptability). There was no significant difference in tumor-to-background ratio and liver signal-to-noise ratio among all the images acquired for 8 min or longer. In the matched study, no significant difference was found in the image quality score and quantitative parameters between the ultra-low-activity group with an 8-min acquisition and the full-activity group with a 2-min acquisition. Conclusion: An ultra-low ¹⁸F-FDG activity with an 8-min acquisition in a total-body PET/CT study can achieve acceptable image quality equivalent to that in the full-activity group after a 2-min acquisition.

Keywords: image quality; total-body PET/CT; ultra-low activity.

Graphical abstract

FIGURE 1.

PET images of 63-y-old man with esophagus cancer. Coronal slice of whole body (A), transverse view of intense uptake of lesions in esophagus (B), and transverse view of liver (C) are shown in G1, G2, G4, G8, G10, and G15 reconstructions. More superior image quality of liver was observed in G8 than in G1 and G2 on visual assessment.

FIGURE 2.

Box plot of lesion SUV_max (A), liver SUV_max (B), TBR (C), liver SUV_mean (D), liver SD (E), and SNR (F). Lesion SUV_max, TBR, and SNR increased with extension of acquisition time, whereas liver SUV_max, liver SUV_mean, and SD decreased. Compared with G15, no significant differences for these parameters were found in G8 and G10. *P < 0.05. ns = not significant.

FIGURE 3.

PET images of 63-y-old man with CRC reconstructed in G8 and another 63-y-old man with CRC reconstructed in g2 (A, coronal slice of the whole body; B, transverse view of CRC lesion [arrow]; C, transverse image of liver). Image quality in G8 was comparable to that in g2, which meets standard for clinical diagnosis.

FIGURE 4.

Bar graph of values of subjective image quality score (A) and objective parameters (B) between G8 and g2. Comparable result of qualitative and quantitative analysis was shown between the 2 groups. ns = not significant.