Small lesions detectability with the Biograph 16 Hi-Rez PET/CT scanner and fast imaging protocols: performance evaluation using an anthropomorphic thoracic phantom and ROC analyses

Objectives

The purpose of this study was to evaluate the impact on lesion detectability of fast imaging protocols using ¹⁸F-FDG and a 3-dimensional LSO-based PET/CT scanner.

Methods

An anthropomorphic thoracic phantom was used simulating the anatomical structures of radioactivity distribution for the upper torso of an underweight patient. Irregularly shaped targets of small dimensions, the zeolites, were located inside the phantom in an unpredictable position for the observers. Target-to background ratios and target dimensions were selected in order to sample the range of detectability. Repeated imaging was performed to acquire PET images with varying emission scan duration (ESD) of 1, 2, 3 and 4 min/bed and background activity concentrations of 10, 5 and 3 kBq/mL in the torso cavity. Three observers ranked the targets and a receiver operating characteristic analysis was performed for each acquisition protocol.

Results

Detection performances improved when passing from a short (ESD = 1 min) protocol to longer (ESD ≥ 2 min) protocols. This improvement was established with adequate statistical significance.

Conclusions

Short image acquisition times of 1 min/bed using ¹⁸F-FDG and the specific scanner model considered in the study lead to reduced lesion detectability and should be avoided also in underweight patients.