Proceedings Article | 17 March 2011
KEYWORDS: Spatial resolution, Image filtering, Modulation transfer functions, Image quality, CT reconstruction, Reconstruction algorithms, Computed tomography, Image analysis, Image resolution, Image restoration
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.
