Precision, repeatability, and validation of the localization of cranial landmarks using computed tomography scans

Computed tomography (CT) has brought to the craniofacial surgeon a three- dimensional representation of internal structures. CT scans provide visualization of anatomy for preoperative planning end postoperative evaluation. Beyond visualization, however, a CT scan enables assessment of measurements useful to clinicians and basic scientists. All measurement systems used with CT require the ability to accurately locate regions of interest on the image (i.e., areas, volumes, outlines, curves, surfaces, points). This study evaluates the precision and repeatability of locating anatomic landmarks in three dimensions on CT slice images, and validates these locations using an established measurement system. The average error of landmark position is always less than 0.5 mm and for some landmarks error is negligible. Repeatability studies show that less than 2% of the total variance in our data is due to measurement inaccuracy. Although data collected from CT scans are internally consistent, validation results caution the use of CT data in combination with data collected using calipers or other direct means of measurement.