A Phantom based Study of the Effects Oral Contrast on PET Images from a Phillips GXL PET/CT
Objective: to investigate artefacts caused by oral CT contrast material in the environment of low dose CT attenuation corrected PET.
Methods: containers of various concentrations of iodine and barium based oral CT contrast agent were placed in a cylindrical PET phantom of uniform activity. The phantom was scanned using our standard PET/CT protocol, 140 kVp and 30mAs. Additionally CT number was assessed for linearity and variation with mAs and kVp. Attenuation corrected PET images were assessed for artefacts. A separate phantom was constructed to simulate the movement of contrast agent between CT and PET scans.
Results; mAs had no effect on the HU of oral contrast agent. The HU of oral contrast agents vary inversely with kVp. No significant PET artefacts were observed at clinically anticipated concentrations of oral contrast agent. Artefacts were observed at high concentration of contrast; typically the volume containing contrast agent and no F-18 appeared as intense or more intense that the background on PET. Artefacts occur at concentrations closer to the clinical concentration using iodine based contrast agents than barium based agents. Movement of a volume containing contrast agent between CT and PET scan caused significant and variable PET artefacts.
Conclusions: the presence of oral contrast at clinically indicated concentrations does not significantly effect PET imaging when using low dose CT attenuation. The movement of contrast agents between CT and PET can cause significant and variable PET artefact.