INFLUENCE OF THE DISTANCE OF A METAL FROM THE FIELD OF VIEW PERIPHERY ON CONE-BEAM COMPUTED TOMOGRAPHY ARTIFACTS

Abstract

<h3>BACKGROUND</h3> The presence of metal in the exomass (zone between the x-ray source and the image receptor) negatively affects image quality in cone beam computed tomography (CBCT), which cannot be effectively corrected by metal artifact reduction algorithms. However, considering that a metallic object can assume different positions in the exomass, the distance from the field of view (FOV) periphery could affect this condition. <h3>OBJECTIVE(S)</h3> The aim of this study was to evaluate the influence of the distance of metallic materials from the periphery of the FOV on the behavior of the CBCT artifacts. <h3>STUDY DESIGN</h3> An imaging phantom was custom made with 16 polypropylene tubes filled with a homogeneous radiopaque solution. CBCT scans were obtained by using a Picasso Trio unit adjusted to 90 kVp, 3 mA, and voxel size of 0.2 mm. The phantom was centered on a 5 × 5 cm FOV under protocols varying the composition (titanium or cobalt-chromium), quantity (0, 1, 2, or 3), and distance from the FOV periphery (2 cm, 3.5 cm, and 5.5 cm) of an object in the exomass. Means of voxel values were obtained from the 16 tubes of the phantom and the standard deviation was calculated as a way of measuring the variability values of each acquisition. Analysis of variance and Tukey's test compared separately the mean voxel and variability values between the different protocols (α = .05). <h3>RESULTS</h3> The mean voxel values were significantly lower (<i>P</i> < .05) for titanium at 5.5 cm and for 2 or 3 cobalt-chromium objects at 2 cm. In most conditions, the variability was significantly higher (<i>P</i> < .05) when the metallic object was at 2 cm. <h3>DISCUSSION/CONCLUSIONS</h3> The shortest distance of metallic materials from the FOV periphery had a greater impact on the CBCT artifacts.