Improvement of Anatomic Alignment and Image Quality Using a Respiratory Motion Reduction Block in Oncologic PET/CT

¹⁸F-FDG PET/CT is crucial for cancer diagnosis; however, respiratory motion often causes misregistration between PET and CT images. This study aimed to evaluate the impact of a custom-made respiratory motion reduction block (RRB) in reducing misregistration and improving image quality in ¹⁸F-FDG PET/CT. Methods: The RRB was developed to minimize the effects of respiratory motion. It is a pentagonal block made of Styrofoam designed to compress the upper abdomen. This study included 170 patients who underwent whole-body ¹⁸F-FDG PET/CT. Patients were categorized into 4 groups based on the CT and PET scanning technique used: a control free-breathing (FB) group (breath-holding [BH] CT without RRB and respiration-gated [RG] PET), a control RG group (BH CT without RRB with RG PET), a BH RRB group (BH CT with RRB), and a FB RRB group (FB CT with RRB). Various parameters, including the incidence rate and distance of anatomic misregistration, and signal-to-noise ratio, were measured and compared. Results: For the control FB, control RG, BH RRB, and FB RRB groups, the incidence rates of anatomic misregistration between PET and CT images were 47.1%, 27.5%, 34.0%, and 16.7%, respectively. The mean misregistration distances in these groups were 5.1 ± 6.0, 3.1 ± 5.5, 3.8 ± 6.2, and 1.3 ± 3.2 mm, respectively. Furthermore, the RRB improved the signal-to-noise ratio of the liver. Conclusion: The RRB effectively improved registration between PET and CT images. Our approach is cost-effective and provides respiratory motion suppression not only during PET but also during CT scans. The use of RRB with FB PET scanning was found to be more beneficial than respiratory gating.