usefulness of respiratory-gated pet acquisition during delayed 18f-fdg pet/ct scanning for patients with liver metastases

Objective(s): to assess respiratory-gated (rg) positron emission tomography (pet) acquisition for patients with liver metastases during delayed pet/computed tomography (ct) scanning with fluorine-18-fluorodeoxyglucose (18f-fdg). methods: nineteen patients with liver metastases who had undergone early whole-body 18f-fdg pet/ct scans without the rg technique and delayed scans with the rg technique were retrospectively selected. the maximum standardized uptake value (suvmax) of 41 liver lesions and the tumor-to-liver uptake ratios (tlrs) for these same lesions were compared among three data sets: early non-respiratory-gated (early non-rg) images, delayed non-respiratory-gated (delayed non-rg) images, and delayed respiratory-gated (delayed rg) images. in the delayed non-rg and delayed rg images, the improvements in the tlr, relative to the early non-rg images, were assessed according to lesion size. results: for liver lesions, the suvmax of early non-rg, delayed non-rg, and delayed rg images were 6.58±2.34, 7.69±3.08, and 9.47±3.73, respectively. there were significant differences among the three images (p<0.01). the tlr of the delayed rg images was significantly higher than those of the early non-rg and delayed non-rg images (p<0.01). in the delayed rg images, the difference in the tlr improvement for lesions ≤10 mm in size was 15% higher than that for lesions >10 mm in size; in the delayed non-rg images, the difference in the tlr improvement for the same lesion categories was 6%.conclusion: delayed rg imaging improves the tlr, compared with early non-rg and delayed non-rg imaging, especially for small lesions. rg pet acquisition may be a promising protocol for assessing liver metastases on delayed pet/ct scans.