Correlation between barium contrast agents and the artifact in PET/CT images.

Objectives We have been found various artifacts disturbing interpretation of PET/CT images. The main factors that may cause the artifacts in PET/CT images were contrast media, patient motion, prosthesis, etc. The purpose of this study was to recognize the correlation between the density of barium contrast agents and artifacts in PET/CT images with the phantom test.

Methods Small inserts with various barium sulfate concentration were inserted into cylindrical phantom. 12 small inserts had a cylindrical shape(diameter 18 mm, volume 43 ml) and have filled up with barium concentrations ranging from 1.5 to 200% W/V. We acquired PT/CT images for cylindrical phantom that filled with F-18 solution( F-18 80±1 MBq, water 6700 ml). Also, CT images were acquired and then PET data were acquired after moving the phantom to simulate the motion artifact. In other words, we acquired CT images of the cylindrical phantom that was placed in PET scanner by aligning its center axis to the axis of the gantry and then acquired the PET data with a spacing 2 mm ranging from 0 to 10 mm. The PET data were reconstructed with OSEM algorithm. We measured the coefficient of variation(CV) around the small insert to get to know whether the barium concentrations have any effect toward the variation of the signal to noise in the PET/CT image.

Results If the CV is over 14.2%, the false positive regions appeared around the other barium small inserts except 1.5 % W/V in CT based attenuation correction of PET images. The barium contrast 40 % W/V exhibited a strong opaque with high hounsfield unit (2951±92) and showed the ring artifact in the vicinity of itself. Additionally, barium concentration caused by the artifacts was lower by 10% W/V when the mismatched spacing between the PET image and the CT image was over 4 mm. However, the artifact by barium contrast agents not appeared in the non attenuation corrected PET images.

Conclusions High density barium contrast lead to the false positive image in PET/CT. If there is the motion at the portion that exists the high density barium, the effect of the artifacts could be further increased.