The effect of independent film and object rotation on projective geometric standardization of dental radiographs.

Digital alignment of dental X-ray images using projective invariants has been shown to be a feasible method for detecting changes through digital subtraction radiography. Previous research on the validity of the standardization procedure has considered the effects of motion of the X-ray source alone. Here the effects of independent motion of the film and the object on the standardization are investigated. This is accomplished by fitting a wire grid to the X-ray source, which allows for correction of film motion separately. The usefulness of separating the motion corrections is discussed, as well as some possible sources of error in the overall standardization procedure. The results of the standardization were found not to differ significantly whether the motions were corrected for separately or simultaneously.