Extraoral control of geometry for digital subtraction radiography

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Abstract
The use of a cephalostat to stabilize projection geometry for subtraction radiography was investigated. Six replicate repositionings of patients within a cephalostat indicated that the mean angular disparity between repositioning was 0.33 ± 0.10 degrees. Subtraction images produced from films of a phantom with artificial periodontal defects exposed using the cephalostat or stent technique were compared. There was no significant difference in the standard deviations of the gray level histograms obtained using the two methods. However, the ability of 10 investigators to detect the presence or absence of simulated periodontal lesions was superior from subtraction radiographs produced from cephalostat‐based images when compared to stent‐based images (p < .02). Sets of radiographs taken of 6 patients on the same day or 3 months apart indicate that the cephalometric technique may be used to stabilize projection geometry.