Magnification of liner measurement on the image of Galileo CBCT scan

XU Ge; SHI Sheng-gen; YAN Shu; WU Bao-jiang

doi:10.15956/j.cnki.chin.j.conserv.dent.2015.07.007

Abstract：AIM: To investigate the magnification on cone beam computed tomography ( CBCT ) images. METHODS:A homemade polymethylmethacrylate plate with 72 grooves filled with zinc oxide cement radiopaque lines was prepared by the CNC machine tools. The lines parallel with the coronal plane, sagittal plane and perpendicular to the horizontal plane were defined as X-, Y- and Z-axis lines respectively. Every 2 axes divided the plane into 4 quadrants and each quadrant contained 2 axial lines and 9 lines on each axis. First, the mould was put into FOV of CBCT and the observation surface was consistent with the horizontal plane of FOV. The center of the observation surface was coincided with the center of FOV. This observation surface was called plane H, and then the plane upper and lower at 20 mm and 40 mm to plane H was scanned respectively for 5 times. Second, the observation surface was made perpendicular to the horizontal plane and parallel to the coronal plane and the center of the observation surface coincided with the center of FOV. This surface was called plane C, and then the plane anterior and posterior at 20 mm and 40 mm to plane C was scanned for 5 times. The distance of the center of radiopaque lines departing from the FOV center was defined as R. The length of each radiopaque line was measured for 6 times, and the magnification was calculated. RESULTS: The maxi-mum magnification of X-axis, Y-axis and Z-axis lines were 3. 4%, 3. 3% and 3. 3% respectively(P>0. 05). For the same line, the magnification of its image that stayed away from the center plane was larger than that close to center plane (P<0. 05) and as for different lines in the same plane, the magnification of the lines staying away from the center of the <br> plane was larger than that close to it(P<0. 05). X-axis magnification was greater than Y-axis or Z-axis (P<0. 05), while the Y-axis and Z-axis magnification was closer (P >0. 05). Magnification was positively associated with R (P<0. 05). CONCLUSION:CBCT images may have a certain magnification of the scanned objects, which is positively associated with the distance from the objects to the FOV center.