Application of a Video Image Subtraction System to Measure and Control Head Position in Cephalometry

Variation in head position in the cephalostat is a potential source of error in cephalometrics as it causes distortion of the radiographic projection of the head. Image subtraction is an electronic technique enabling images to be superimposed and which highlights any differences. Using this method, a study was carried out to assess the reproducibility of the position of the head in the cephalostat. It was also used to find out whether subjects could improve their own head relocation by looking at the monitor and trying to achieve the best possible fit on the original image.