[The influence on the images of computed tomography caused by the use of artificial cranial reconstructive materials]

Various materials have been used for cranioplasty; however, these materials frequently produce artifacts that appear when examined with conventional radiography. Computed tomography (CT), in particular, detects high density artifacts near artificial bones, which is manipulated by increased noise, and limits diagnostic performance. The purpose of this study was to evaluate the extent and shape of the artifacts due to artificial cranial bones and to consider CT imaging parameters necessary for accurate recognition of structures under the materials. Four different artificial bone materials were evaluated in this study: hydroxyapatite with 1) 40% or 2) 50% porosity, 3) titanium plate, and 4) hydroxyapatite-polymethylmethacrylate composite (HA-PMMA). CT scanning was performed with standard clinical settings. Sample specimens were placed on the right side, under the artificial bones, and CT was performed to evaluate specimen visibility. We compared the artifacts created by the four bone types listed above, and measured the CT values of those materials. With ordinary scan settings, all the artificial bones revealed high-density artifact surrounding the materials, including the inability to accurately measure specimen thickness. The upper part of the specimen in contact with the artificial bones could not be distinguished from the artifact. The CT value in the medial aspect of the artificial bones increased more than the actual CT values. Of the four artificial bone materials studied, HA-PMMA produced the fewest artifacts. Description of the structures under the artificial bones can be improved by extending the window width to approximately twice that of normal settings.