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The accuracy in imaging small high-density structures is compared for 16 and 64 multidetector-row computed tomography (MDCT) scanners.Phantom experiments and different quantification methods are used to establish size measurement accuracy, object signal, and image noise, for both MDCT systems.At similar scanning doses, image noise is larger (∼55%) for the 64 MDCT compared with the 16 MDCT, leading to lower signal-to-noise ratios (∼28% for objects <2 mm). Object spread in the xy-plane is similar for both systems; while it is reduced along the z-axis (by ∼0.18 mm) for the 64 MDCT. Measurement accuracy of the 64 MDCT is not significantly higher (P < 0.05) compared with the 16 MDCT when using a relative-threshold corresponding to 50% of the object maximum attenuation value. However, when using a fixed-threshold, interscanner and interprotocol measurement differences are statistically significant (eg, volume relative errors are reduced by ∼17% on average for the 64 MDCT).Measurement accuracy of the 16 and 64 MDCT scanners is not significantly different when using a 50% relative threshold. However, image noise is significantly larger for the 64 MDCT. Compared with a fixed-threshold based method, the 50% relative-threshold strongly reduces interscanner and interprotocol measurement dependency and improves accuracy.