An evaluation of the reproducibility of landmark identification using scanned cephalometric images

A method of cephalometric analysis is described in which cephalometric x-rays were scanned using a flat-bed scanner and transparency hood. Then the image was displayed on a computer monitor for point identification and subsequent cephalometric analysis using dedicated software. The reproducibility of point identification using this method was compared with two other, commonly used, methods.

The study material comprised 25 lateral skull x-rays taken as part of routine orthodontic assessment. Repeat cephalometric point identification was carried out on each x-ray using 3 methods: 1. On-screen digitization of the scanned bitmap image (Screenceph method). 2. Tracing followed by digitization of the identified points and 3. Direct digitization.

For the 8 angular and 4 linear cephalometric measurements examined the Screenceph method compared favourably with the two conventional methods. The median difference between methods was 0.5 degrees and 0.2 mm. Using constructed Cartesian axes to examine the x, y discrepancy between repeat measurements and comparing Screenceph to tracing followed by digitization, there were significant differences in 3 instances at the 5% level and 2 instances at the 1% level. These differences represented median scores of 0.14 to 0.32 mm greater for Screenceph. Comparing Screenceph to direct digitization 15 significant differences out of the 28 measurements were noted: six at the 5% level and 9 at the 1% level. The actual difference in median scores ranged from 0.2 mm to 0.53 mm.

The results demonstrated that Screenceph is sufficiently accurate to use in a clinical setting but is not yet sufficiently exact for use in research projects owing to hardware limitations.