Extent of projection reduction in XCT dimensional measurements using OS-SART under beam-hardening effects

X-ray computed tomography (XCT) is widely used for dimensional measurements; however, long scan time limits its efficiency. Reducing projections is effective to accelerate scanning, but the achievable extent of projection reduction while maintaining measurement accuracy comparable to conventional reconstruction remains insufficiently quantified. This study investigates the feasibility of projection reduction in XCT dimensional measurements using the ordered-subsets simultaneous algebraic reconstruction technique (OS-SART). Sizes and form deviations are evaluated on two representative geometries: multi-stepped cylindrical geometry and more complex prismatic geometry. To account for material-related effects, the analysis is conducted on both aluminum and titanium parts. The Feldkamp–Davis–Kress (FDK) algorithm with full projections is used as a reference. Results show that, for the cylindrical geometry, OS-SART maintains measurement accuracy comparable to FDK under substantial projection reduction, despite differences in material. In contrast, for prismatic geometry, projection reduction is strongly constrained when conventional beam-hardening correction (BHC) is applied. Further analysis reveals OS-SART is considerably more sensitive to BHC strength, particularly for complex geometrical features, and this trend is consistent across materials. To address this limitation, a slice-based BHC level selection strategy is proposed and validated through experimental and simulation studies. Quantitatively, projection reduction of approximately 75% is achieved for cylindrical geometries, whereas for prismatic ones the achievable reduction is limited to about 50% even with optimized BHC. These findings demonstrate that projection reduction in XCT measurements is governed by the interplay among part geometry, beam-hardening effects, material attenuation, and reconstruction algorithm, providing practical guidance for efficient XCT measurements.