Impact of X-ray tube settings and metallic leads on neurological PET imaging when using CT-based attenuation correction

The use of X-ray CT images for CT-based attenuation correction (CTAC) of PET data results in the decrease of overall scanning time and creates a noise-free attenuation map (μmap). Given that different tube voltages and currents are used in clinical PET/CT scanning protocols depending on patient size and the body region under study, this work was designed to evaluate the effect of tube settings and the presence of deep brain stimulation (DBS) metallic leads on the accuracy of CTAC. A commercial anthropomorphic head phantom and an in-house made polyethylene phantom were used in order to quantitatively measure the effect of the nominated parameters, using quantitative analysis of created μmaps, generated attenuation correction factors and reconstructed neurological PET emission data. A maximum absolute relative difference of 0.9% was observed between average CT numbers of images acquired at 300 mA and those acquired with tube currents from 20 to 280 mA in steps of 20 mA. Slopes equal to 5.79×10−5, 5.34×10−5 and 3.92×10−5 for calibration curves corresponding to CT numbers greater than 0 HU were obtained at tube voltages of 140, 120 and 80 kVp, respectively. A relative difference of 36% and 27% for CT numbers of cortical bone measured at 80 kVp were observed in comparison with images acquired at 140 and 120 kVp, respectively. It was concluded that the attenuation map derivation is independent of tube current used for the settings explored in this work. Likewise, the visual qualitative interpretation and quantitative analysis of neurological PET emission images is independent of X-ray tube voltage. The DBS metallic leads do not create any visible or quantifiable artifacts in the reconstructed neurological PET images owing to their small size.