Quantitative accuracy and clinical utility of ultra-low dose CT protocols for attenuation correction in PET/CT

Abstract Purpose In PET/CT imaging, CT frequently accounts for more than 50% of the total radiation exposure, even when used solely for attenuation correction and anatomical localisation. This poses a major limitation for dose-sensitive populations, including pregnant women and paediatric patients. This study systematically evaluated the impact of ultra-low-dose (ULD) CT acquisition strategies, including spectral shaping, on PET quantification and task-based performance using phantom and clinical data. Methods NEMA phantom experiments were performed to characterise the effects of progressive CT dose reduction on CT image quality, attenuation map accuracy, and PET quantification. An optimal ULD protocol was then prospectively validated in clinical [ 18 F]FDG and [ 68 Ga]DOTATATE PET/CT studies. PET images reconstructed using ULD and standard-dose (STD) CT were compared using regional SUV metrics, voxel-wise error analysis, structural similarity, lesion detectability, and concordance of SUV-based clinical classifications. Results Phantom experiments demonstrated that tin-filtered ULD CT achieved >90% reduction in CT effective dose while preserving accurate attenuation correction and PET quantification. The selected protocol (Sn140 kV $$_{\\textrm{p}}$$ , 6 mAs) provided an optimal balance between dose reduction and image quality, avoiding artefacts and maintaining robust performance across quantitative PET metrics. In clinical validation, regional SUV $$_{\\textrm{mean}}$$ differences between ULD and STD reconstructions were negligible (mean bias −0.005 (−0.33%) for [ 18 F]FDG and −0.025 (−0.72%) for [ 68 Ga]DOTATATE), with narrow Bland–Altman limits of agreement across organs. Voxel-wise differences were primarily driven by respiratory misalignment rather than CT noise. Lesion detectability, SUV $$_{\\textrm{max}}$$ , and SUV $$_{\\textrm{peak}}$$ were preserved, with >95% concordance across clinically relevant SUV thresholds. Conclusion Tin-filtered ultra-low-dose CT enables genuinely low-dose whole-body PET/CT, achieving total effective doses below 1 mSv while preserving quantitative accuracy, lesion conspicuity, and clinical interpretability. This approach offers an immediately deployable pathway to safer PET/CT imaging, with particular benefit for pregnant and paediatric patients.