Effect of sitting, standing, and supine body positions on facial soft tissue: detailed 3D analysis.

Medical imaging techniques require various body positions. Gravity causes changes in the facial soft tissue and acts in different directions according to the position of the head during imaging. The aim of this study was to evaluate the effect of positional changes on the facial soft tissue. The faces of subjects were scanned in the standing, sitting, and supine body positions. Differences in the positions were compared using the root mean square (RMS), mean absolute deviation (MAD), and mean signed distance (MSD). The displacement of 15 midsagittal and 20 bilateral landmarks was evaluated. The RMS, MAD, and MSD values of the sitting-standing comparison were significantly lower than those of the sitting-supine and standing-supine comparisons. There were no significant differences between the sitting-supine and standing-supine comparisons. Sixteen out of 135 measurements (12%) of the midsagittal landmarks and 94 out of 180 (52%) measurements of the bilateral landmarks showed significant displacements among the body positions. These results demonstrate a significant change in the facial soft tissue caused by body position. Furthermore, these data show the different susceptibilities of the facial soft tissue landmarks to the effect of body position along the x, y, and z axes.