Use of gray values in CBCT and MSCT images for determination of density: influence of variation of FOV size.

Abstract

To determine the effect of field of view (FOV) size on gray values in cone beam computed tomography (CBCT) and multislice computed tomography (MSCT) images. A phantom made up of 3 cylinders containing distilled water, plaster, and motor oil was constructed and inserted into an acrylic cylinder filled with distilled water. The phantom was scanned with a CBCT and MSCT device using 3 FOV sizes. Gray value of each material was evaluated in 40 axial slices, and the comparison between the results obtained with the same FOV size was made. In CBCT examinations, there was significant difference between the gray values of different FOVs for the 3 materials. In the MSCT, there was significant difference for the oil. Gray values showed significant difference between the CBCT and MSCT examinations for the 3 materials in the 3 different FOV sizes. Gray values determined in CBCT images are significantly influenced by the FOV size. Although the gray values obtained in MSCT have shown statistically significant differences between some acquisitions, the analysis of those differences seems to indicate low clinical relevance.