Optimal activity of [18F]FDG for Hodgkin lymphoma imaging performed on PET/CT camera with BGO crystals

We aimed to find the minimum feasible activity of fluorodeoxyglucose ([18F]FDG) in positron emission tomography/computed tomography (PET/CT) of Hodgkin lymphoma patients performed on a camera with bismuth germanate (BGO) crystals.

Ninety-one [18F]FDG PET/CT scans (each in seven Bayesian Penalized Likelihood [BPL] reconstructions with varying acquisition time per bed position - 2 min, 1.5 min, 1 min, 50 s, 40 s, 30 s, and 20 s) were independently assessed by three physicians to evaluate image quality. Mean administered activity was 3.0 ± 0.1 MBq/kg and mean uptake time was 54.0 ± 8.7 min. The series quality was subjectively marked on a 1-10 scale and then ranked 1-7 based on the mean mark. Interobserver rank correlation and intraclass correlation within each series for the three observers were calculated. Phantom studies were also performed to determine if reduced acquisition time can be directly translated into a reduced activity.

Time series were marked and ranked unanimously - the longer the time of acquisition the higher the mark and rank. The interobserver agreement in the ranking was excellent (100%) with a kappa coefficient of 1.00 (95% CI [0.83-1.0]). The general intraclass correlation coefficient (agreement between the marks observers gave each time series) was very high (0.945, 95% CI [0.936-0.952]) and was higher the shorter the time per bed. According to all three observers only the series with 2 min and 1.5 min acquisition time were appropriate for assessment (mean mark ≥ 7). In phantom studies there was a linear correlation between time per bed, administered activity, and number of total prompts detected by a scanner. Hence, a reduction of acquisition time of 25% (from 2 min to 1.5 min) could be directly translated into a 25% activity reduction (from 3.0 to 2.25 MBq/kg).

In patients with HL, [18F]FDG activity can be reduced by up to 25% when using a BGO crystal camera, without substantial impact on image quality.