Effects of different hydration protocols on image quality of half-dose 18F-FDG total-body PET/CT: A prospective study

Introduction: This study aimed to investigate the effects of volume and time of hydration on image quality when performing ¹⁸F-FDG total-body PET/CT with half-dose activity.

Methods: A total of 210 patients were prospectively enrolled in this study and underwent total-body PET/CT with half-dose (1.85 MBq/kg) of ¹⁸F-FDG activity. Among them, 180 patients were randomized into 6 hydration groups (30 patients each group) with different volumes of water and time: oral hydration with 500 ml of water 20 min before (500 ml-20 min-B), 5 min after (500 ml-5 min-A), and 30 min after (500 ml-30 min-A) the ¹⁸F-FDG injection; oral hydration with 200 ml of water 20 min before (200 ml-20 min-B), 5 min after (200 ml-5 min-A), and 30 min after (200 ml-30 min-A) the ¹⁸F-FDG injection, respectively. Another 30 patients underwent dynamic imaging without hydration and were considered as the non-hydration control group. The image quality among the 7 groups was evaluated both subjectively and objectively. The subjective image quality analysis was conducted according to the Likert scale (5-excellent, 1-poor). The objective analysis included the measurements of SUVmax of the same blood pool, muscle, and liver, as well as the signal-to-noise ratio (SNR) of the liver.

Results: With the subjective evaluation, there was no significant difference (all, p>0.05) of the subjective image quality scores of the blood pool (ranging from 4.32 to 4.37), muscle (4.23 to 4.33), and liver (4.02 to 4.08), as well as the MIP (4.11 to 4.20) among the 6 hydration groups. However, the scores of the blood pool (3.82), muscle (3.9), and liver (3.45), as well as MIP (3.8) in the non-hydration group were all significantly lower than those in the hydration groups (all, p<0.05). With the objective evaluation, the SUVmax of the blood pool was lower in the 500 ml group (1.72) compared to the 200 ml group (1.86). The SUVmax of the blood pool was lower at the early time point (20 min-B) than the later time points (5 min-A and 30 min-A), with 1.72, 1.80, and 1.85 respectively (p<0.05). The SUVmax of the muscle was also lower at the early time point than the later time points (0.68, 0.70, and 0.78 respectively, p<0.05). The SUVmax of the blood pool at each of the 3 time points in either the 500 ml or 200 ml groups was significantly lower than in the non-hydration group (2.33). There was no difference in SUVmax in the liver and the liver SNR among the 6 hydration groups. Although the non-hydration group showed higher liver SUVmax compared to the 6 hydration groups, there was no difference in the liver SNR between the non-hydration and 6 hydration groups.

Conclusions: When performing total-body PET/CT with a half dose of ¹⁸F-FDG activity, a high volume (500 mL) of water orally administered at an early time point (20 minutes before ¹⁸F-FDG injection) showed improved background compared to a lower volume (200 mL) of water orally administered at a later time (5 or 20 minutes after injection). However, 200 mL of water was sufficient to reduce ¹⁸F-FDG activity in the liver and muscle, while the timing of hydration did not affect the image quality of the liver.