Significance of the Position of the Craniofacial Computed Tomographic Scanning

ABSTRACT

The computer imaging process is becoming a popular procedure in the research of the craniofacial skeleton. In acquisition of the digital data of computer tomography (CT), the position of the head is likely to vary each time. The difference in head position results in different orientations on actual images, which in turn may result in misinterpretation of the image. The purpose of this study is to point out the importance of position alignment between CT databases before pursuing research by comparing the images of different position alignment To show the significance of the alignment of CT scan, eleven target points were selected from CT scan and the coordinates were obtained from the different position of the aligned CT scan by the nasion, basion, and bilateral external auditory meatus. The target points were divided into three groups-the central points, the lateral points, and the mid points groups, depending on their positional configuration from the mid- sagittal plane. The alignment of CT scan was processed by volume rendering method and the coordinates of target points were taken from the three dimensional images with different position. The aligned CT images rotated by 10 degrees with respect to the X-axis, the (X- and Y-axes), and the (X-, Y-, and Z axes), respectively. Eleven target points were measured from these rotated images one per day, for 10 days, by a plastic surgeon. The mean coordinates from the 10 trials were defined as the gold standard values for the other 10 times measurement. The measurement error(ME) of the central points group was lower than that of the mid points group, and the ME of the mid points group was lower than that of the lateral points group. The ME increased as the distance from the center to target point increased. However the ME of aligned CT images was the lowest of all the rotated cases. For the mean ME of the 11 points, aligned image, the X-axis(X- and Y-axes), and (X-, Y-, and Z-axes) rotation were 0.97, 1.53, 1.62 and 1.77 mm, respectively. Among three rotated cases, ME of the(X-, Y-, and Z-axes) rotation had the highest one. Above results mean that the chance of incorrectly localizing the target points could be significantly reduced if the skull CT images were aligned, in the research of the measurement of craniofacial skeleton from CT scan.