Impact of scatter limitation correction on photopenic artifacts caused by patient motion during whole-body PET/CT

Objectives Overcorrection of scatter caused by patient motion during whole-body PET/CT can result in photopenic artifacts appearing on PET images. The present study aimed to quantify the accuracy of scatter limitation correction (SLC) for scatter-correction error.

Methods This retrospective study analyzed photopenic artifacts on ¹⁸F-FDG PET/CT images acquired from 12 patients and from a NEMA phantom that simulated the human body equipped with two peripheral plastic bottles (diameter, 7 cm) to simulate arms. The NEMA body phantom comprised a sphere (diameter 10 or 37 mm) in F-18 solutions with target-to-background ratios (TBRs) of 2, 4 and 8. The plastic bottles were arranged to induce photopenic artifacts during PET image acquisition after CT. All PET data were reconstructed using model-based scatter correction (SC), no scatter correction (NSC), and scatter limitation correction (SLC).

Results Applying NSC and SLC substantially eliminated the photopenic artifacts of SC on PET images acquired from the patients and the phantom. Quantitative indices could not be evaluated with NSC, but SLC allowed calculations of standardized uptake values (SUV). Since SLC limits the amount of out-of-field scatter only when the scatter fraction exceeds a specific threshold, SLC did not affect the SUV when CT and PET were perfectly aligned. The scatter fraction was considerably lower for SLC, than for SC PET images. A smaller sphere and a lower TBR resulted in increased activity concentration degradation of SC images of the phantom. The SLC improved the activity concentration of the sphere for all TBR, particularly the 22.0% and 58.3% errors in SLC and SC images, respectively, when the TBR of the spheres was 2.

Conclusions The SLC corrected photopenic artifacts due to scatter-correction error with a small residual error. The SLC is useful and practical for clinical qualitative and quantitative PET/CT assessment.