Influence of Ultra-Low-Dose CT on PET Image Quantification and Visual Assessment

Recent advances in high-sensitivity PET allow for significantly reduced radiation doses, making the CT radiation dose a larger fraction of the total scan dose. This is the first study to the best of our knowledge that evaluates the feasibility and efficacy of an ultra-low-dose CT (ULD-CT) protocol, incorporating a Sn filter, by reducing radiation exposure while maintaining PET image quality and quantitative accuracy in oncology patients. Methods: The study involved 29 oncology patients. FDG PET/CT scans were performed using both low-dose CT (LD-CT) and ULD-CT protocols. The ULD-CT protocol used the Sn filter with 100 kVp and 6 mAs, whereas the LD-CT protocol, optimized for PET attenuation correction and anatomic localization, was performed without the Sn filter, using 100–120 kVp and 12–30 mAs. Quantitative and qualitative comparisons of PET images were made, focusing on SUVs, Patlak analysis, and diagnostic quality on different tissues. Results: The ULD-CT protocol reduced the CT radiation dose by 97%, from 1.93 ± 0.61 mSv to 0.059 ± 0.026 mSv. SUV comparisons showed relative variations of less than 3%. The net rate of influx values resulting from the Patlak reconstruction showed negligible differences across various tissues between ULD-CT and LD-CT PET reconstructions. Image quality assessments revealed no significant differences between ULD-CT and LD-CT PET reconstructions, with consistently high scores (greater than 4 on a 5-point Likert scale). Lesion detection analysis showed strong intraobserver agreement (intraclass correlation coefficient > 0.85) without significant differences in lesion localization. Conclusion: The ULD-CT protocol substantially reduces radiation exposure in PET/CT while maintaining diagnostic quality of PET scans and introducing negligible quantitative effects, thereby paving the way for optimizing CT radiation protocols in PET/CT imaging.