Impact of patient centering on radiation dose and image noise in computed tomography: noise reduction potential of adaptive statistical iterative reconstruction

Abstract

Background The effect of patient miscentering on CT bowtie filter performance has been documented in prior studies; however, quantitative data spanning wide offset ranges and multiple reconstruction configurations remain limited. Methods A Catphan® 500 phantom was scanned at eleven vertical offsets (−5.75 to +14 cm from the isocenter) on a GE Healthcare Optima CT system (120 kVp, 200 mA) using standard and soft kernels combined with filtered back projection (FBP) and Adaptive Statistical Iterative Reconstruction (ASIR). A 32 cm PMMA body phantom was scanned at five positions for point dose assessment at the standard CTDI phantom measurement locations. Results With the standard kernel and FBP, noise magnitude (standard deviation) increased by 27.22% at +14 cm. ASIR reduced noise magnitude by 37–40% at all positions but did not eliminate the centering-induced noise penalty. The point dose at the posterior peripheral position (6H) increased by 47.88% at −8 cm, while the anterior position (12H) decreased by 27.94%. The weighted CTDIw remained within ±5%. Conclusion Miscentering induces position-dependent point dose redistribution and progressive noise magnitude increase. ASIR attenuates but does not fully compensate the noise penalty. CTDIw may mask local dose heterogeneity. These findings require confirmation with anthropomorphic phantoms, noise power spectrum analysis, and observer-performance studies.