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Computer imaging helps profile facial reconstructive surgery

Jun 2007
Raquel Harper

Reconstructive surgery can help patients acquire facial harmony. Those benefiting include children with craniofacial disorders and patients with teeth that do not line up. Before surgery, plastic surgeons must accurately analyze the face to make sure that all of the facial features, such as the chin and nose, will be well-balanced in relation to the structures around them. However, the standard method of analysis is based on the surgeon’s artistic eye — meaning that the amount of change is dependent on the surgeon’s judgment.

Dr. Travis T. Tollefson and Dr. Jonathan M. Sykes from the University of California, Davis, Medical Center in Sacramento devised a calibration technique that can be used to standardize pre- and postoperative photographs using computer imaging, providing surgeons and patients with exact dimensions. “Before, we didn’t have a number that we could talk to the patient about. We would just adjust it by art — saying we wanted the chin to come out this far and the nose to go back that far,” Tollefson said.

He explained that, traditionally, pre- and postoperative photographs of each patient were taken with one digital camera but by several people. This meant that the dimensions between the before and after photographs would always be slightly different. A method was needed to synchronize the two sets of photographs.

Figure 1. Researchers developed a calibration technique that can be used to help guide facial reconstructive surgery with computer imaging software. A computer-generated 3-D image is shown before the child had craniofacial surgery.

The researchers realized that no matter which facial measurements might change, the ear canal would always be the same distance from the pupil. They used this distance as a constant for calibrating pre- and postoperative photographs.

They also discovered another constant, the iris, which has a fairly standard size for all humans (and all ages) of about 11 ±0.5 mm high. This meant that, if in one photograph the iris was 6 mm tall, the investigators could adjust it to be about 11 mm, and the rest of the photograph could be increased proportionally.

Using the control distance from the top of the external ear canal (the porion) to the pupil, as well as the distance from the ear canal to the most prominent point on the chin (the pogonion), in addition to the constant size of the iris, the researchers developed a standard scale for before and after photographs that could be compared using computer imaging software. They then added the following established measurements to their analysis method (as seen in A, B and C in the illustrations in Figure 2): the cervicomental angle (formed by a line drawn tangent to the bottom of the chin and a line tangent to the neck, A); the mentocervical angle (formed by a line drawn from the nose to the chin and tangent to the neck, B); and the facial convexity angle (formed by a line drawn from the forehead to the chin and from the bottom of the nose to the chin, C).

Figure 2. Using computer imaging software, pre- and postoperative photographs were analyzed with the researchers’ new method of chin evaluation and with established measurements, including the cervicomental angle (A), the mentocervical angle (B) and the facial convexity angle (C). Reprinted with permission from the Archives of Facial Plastic Surgery.

The researchers tested 14 patients undergoing combined rhinoplasty (nose surgery) and chin correction. They took pre- and postoperative photographs with a digital camera from Sony of Tokyo. The photographs were analyzed using Marketwise Hi-Res 7.0 computer imaging software from United Imaging of Winston-Salem, N.C., into which all of their established calculations and measurements had been entered.

They found that all of the postphotograph angle measurements changed from those in the preoperative photographs toward an established normal range. The researchers believe that their calibration technique can be used as an effective guide for profile facial analysis. The computer imaging software can be used to show surgeons and patients exactly what kinds of changes can be made (presurgery) as well as to provide accurate measurements for postoperative review.

Archives of Facial Plastic Surgery, March/April 2007, pp. 113-119.

digital camera
A camera that converts a collected image into pixels that are black or white digital or shades of gray. The digital data may then be manipulated to enhance or otherwise modify the resulting viewed image.
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