Investigation of Noise Level and Spatial Resolution of CT Images Filtered with a Selective Mean Filter and Its Comparison to an Adaptive Statistical Iterative Reconstruction

Abstract

Objective: The aim of this study is to investigate image qualities filtered by a selective mean filter (SMF) and its comparison to an adaptive statistical iterative reconstruction (ASIR).Materials and Methods: A CT AAPM performance phantom was used for the assessment of basic image quality. The phantom was scanned by 128 Multiple Slices Computed Tomography. The tube current was varied (i.e. 50, 100, 150, and 200 mA). The images of a phantom were reconstructed by FBP followed by SMF and ASIR (20, 40, 60, 80, and 100%). The image quality assessment was in terms of noise level, noise power spectrum (NPS), and modulation transfer function (MTF). Result: It was found that SMF reduced noise level by more than 65% compared with FBP. The noise level and NPS of SMF was similar with ASIR 100%. The values of the MTF10 and MTF50 of the FBP, ASIR filter at any level, and SMF were comparable. The MTF10 values of FBP, ASIR 60% and SMF with 50 mA (low) tube current were 0.747 ± 0.03, 0.755 ± 0.02, and 0.748 ± 0.02 cycle/mm, respectively. While the MTF10 of FBP, ASIR 60%, and SMF with 200 mA (high) tube current were 0.730 ± 0.00, 0.741 ± 0.00, and 0.732 ± 0.00 cycles/mm, respectively. The MTF50 values of FBP, ASIR 60%, and SMF with low tube current were 0.408 ± 0.05, 0.428 ± 0.03, and 0.446 ± 0.04 cycle/mm, respectively. While the MTF50 values of FBP, ASIR 60%, and SMF with high tube current were 0.416 ± 0.00, 0.428 ± 0.01, and 0.416 ± 0.00 cycle/mm, respectively.Conclusions: These results indicated that the SMF algorithm reduces noise level without affecting the spatial resolution. The performance of the SMF in reducing noise is equivalent to the maximum level of ASIR strength i.e. ASIR 100%.