Localiser-Based Software-Assisted Patient Positioning in Chest CT: A Propensity Score-Matched Study

Background/Objectives: Vertical off-centring in chest CT impairs bowtie-filter beam-hardening correction, degrading noise uniformity and image quality. iCentering derives the patient's geometric centre from a single posteroanterior localiser and automatically adjusts table height. This study aimed to evaluate whether iCentering reduces off-centring distance (OCD) and improves image quality versus manual positioning in chest CT, and to investigate correlations between OCD and noise characteristics. Methods: In this retrospective, single-centre study, 192 propensity score-matched pairs from 423 adults undergoing non-contrast chest CT were analysed. OCD, objective image quality (standard deviation (SD), signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), figure of merit (FOM)), noise distribution ratio (NDR_A-P), and radiation dose indices were measured. Paired comparisons employed t-tests or Wilcoxon signed-rank tests with 95% confidence intervals (CIs) and effect sizes reported. Directionally stratified Spearman correlation and multivariable regression examined OCD-noise associations. Results: Intra- and inter-observer reliability was good to excellent (ICC 0.87-0.99 for OCD; 0.75-0.97 for most regions of interest). iCentering moved median OCD closer to zero at all levels (Level 1: -7.25 vs. -29.40 mm; Level 2: -1.45 vs. -22.00 mm; Level 3: 7.45 vs. -11.90 mm; all p < 0.001; r range: 0.76-0.77). Regarding image quality, SD decreased and SNR, CNR, and FOM increased at all levels (all p < 0.001), while NDR_A-P approached 1.00 (p < 0.05). Radiation dose indices were unchanged (p > 0.05). OCD correlated with SD (|ρ| = 0.478-0.812, p < 0.001); regression confirmed independent associations in both strata (OCD < 0: β range: -0.068 to -0.079, R² = 0.52-0.65; OCD > 0: β range: 0.056-0.078, R² = 0.28-0.54), whereas the association between OCD and NDR_A-P was weak. Conclusions: iCentering improves centring accuracy and objective image quality in chest CT, without increasing radiation exposure. Reduced OCD is independently associated with lower image noise, underscoring the value of precise centring.