FIG. 3.

Noise-resolution properties of bilateral filtering and body kernels. Noise is expressed as the standard deviation (HU) in a small ROI close to the thin wire. The spatial resolution was quantified as the spatial frequency at 10% of the maximum value on the MTF curve. The solid curve linking the solid triangles (▲) was obtained from the image scanned with 40 mA s and reconstructed with kernels of B10f, B20f, B30f, B40f, and B50f (from left to right). The solid diamond symbol (◆) was from the same scan and represents a special body kernel B25f. The dashed curve linking the open triangles (△) represents the noise-resolution results obtained from images after applying bilateral filtering to the 40 mA s scan data with ten different smoothing parameters. From left to right, the first five points were reconstructed with the B40f kernel, with $w$ fixed at 5, and σ = 2.2, 1.8, 1.4, 1.0, 0.7, respectively; the second five points were reconstructed with a sharper B70f kernel, with $w$ fixed at 5, and σ = 2.8, 2.2, 1.8, 1.4, and 1.0, respectively. The solid curve linking the solid circles (●) was obtained from the image scanned with 80 mA s and reconstructed with kernels of B10f, B20f, B30f, B40f, and B50f (from left to right). The dashed curve linking the open circles (○) represents the noise-resolution results obtained from images after applying bilateral filtering to the 80 mA s scan data with the same ten smoothing parameters as above. The noise-resolution results on the 40 mA s data after bilateral filtering approach or exceed the noise-resolution properties of the 80 mA s data, and filtering is effective on the 80 mA s data as well as on the 40 mA s data.