Characteristics of noise and resolution on image reconstruction in cone-beam computed tomography

The cone-beam computed tomography (CBCT) is a useful modality in diagnostic imaging due to the properties of fast volume coverage, lower radiation dose, easy hardware implementation, and higher spatial resolution. Recently, attention is being paid to address the noise and resolution relationship for CBCT. In CBCT system, image noise and spatial resolution play important roles in image quality. However, there has not been done many works for evaluating the relationship of image noise and the spatial resolution in CBCT. In this study, we evaluated the image noise and spatial resolution as a function of filter, number of projections, and voxel size on reconstructed images in CBCT. The simulated projection data of Catphan 600 phantom were reconstructed using the FDK algorithm. To evaluate the image noise and spatial resolution, the coefficient of variation (COV) of attenuation coefficient and the modulation transfer function (MTF) in axial images were calculated, respectively. The filters used for reconstruction were Ram-lak, Shepp-logan, Cosine, Hamming, and Hann. A number of projections were 161, 321, 481 and 642 acquired from scanning of 360 degree and the voxels with sizes of 0.10 mm, 0.15 mm, 0.20 mm, 0.25 mm and 0.30 mm were used. The image noise given by Hann filter was the lowest and decreased as functions of number of projections and voxel size. The spatial resolution given by Ram-lak filter was the highest and increased as a function of number of projections, decreased as a function of voxel size. The results of this study show the relationship of image noise and spatial resolution in CBCT and the characteristics of reconstruction factors for trade-off between the image noise and spatial resolution. It can also provide information of image noise and spatial resolution for adaptive image.