Elimination of misalignment-induced artifacts in FDG PET/CT by the combination of two different breathing protocols (breath-hold and free breathing) for CT

Objectives In FDG PET/CT imaging, misalignment between PET images and CT images for attenuation correction (AC) causes artifacts in the upper abdomen, leading to misdiagnosis. The CT acquired during breath-hold at shallow expiration (EBH) is widely used for AC. However, misalignment-induced artifacts are sometimes observed. Thereby, we propose the additional CT acquisition during free breathing (FB) so that optimal co-registration of PET/CT images can be achieved. The purpose of this study was to evaluate the usefulness of FB-CT as an alternative AC source to reduce the artifacts in the upper abdomen.

Methods Consecutive 372 patients who underwent FDG PET combined with EBH-CT on GE Discovery 690 were prospectively studied. FB-CT of the upper abdomen was additionally scanned when the misalignment-induced artifacts were observed in the liver or spleen on the PET/EBH-CT images. The severity of the misalignment-induced artifacts of liver and spleen was visually assessed using a 4-point scale (none, mild, moderate, severe), and was compared between EBH and FB protocols. The accuracy of image registration, which was defined as the 3-dimensional distances of the liver and spleen between CT and uncorrected PET images, were also compared between EBH and FB protocols.

Results The misalignment-induced artifacts were observed in 16 (4.3%) of 372 patients on PET images with EBH-CT (liver, severe/moderate/mild/none=8/6/2/0 cases; spleen, 7/2/2/5 cases). By using FB-CT, the misalignment-induced artifacts disappeared in all cases. The accuracy of image registration was significantly improved by using FB protocol in comparison to EBH protocol (liver, 5.1 ± 4.6mm vs. 26.9 ± 8.2mm, p<0.0001; spleen, 3.1 ± 3.2mm vs. 13.9 ± 11.3mm, p<0.0001).

Conclusions The misalignment-induced artifacts in the upper abdomen on FDG PET with CT acquisition during breath-hold at shallow expiration can be eliminated by the additional CT acquisition during shallow free breathing.