Dentomaxillofacial Radiology, Vol 29, Issue 4 223-229, Copyright © 2000 by British Institute of Radiology

ARTICLES

A comparison of the effect of task-specific with fixed beam alignment in tuned-aperture computed tomography

R. L. Webber and J. L. Hendrickson
Wake Forest University School of Medicine, Department of Dentistry, Medical Center Boulevard, Winston-Salem, NC 27157-1093, USA.

OBJECTIVES: To test the hypothesis that fixed beam alignment, representative of conventional, fixed-projection three-dimensional (3D) imaging systems, yields significantly lower detectability of approximal radiolucencies than does a task-specific strategy that 'opens the contacts'. METHODS: Eleven pairs of extracted teeth containing systematically varying numbers of induced approximal low-contrast defects were evaluated from 3D displays produced by means of tuned-aperture computed tomography (TACT) under controlled conditions. Each of the resulting tomographic presentations was displayed in two random sequences to seven trained clinicians. The task-specific (test) series was generated from eight different projections varying in vertical disparity but constrained to open the contacts. The fixed-aiming (control) series was generated from eight projections distributed uniformly on a circle. RESULTS: Accuracy of defect detection averaged 5%, significantly higher with task-specific aiming than with fixed alignment projection geometry (P = 0.02). All observers unequivocally preferred the displays produced from projections with open contacts; however, they demonstrated considerable variation in their approach to the task, including the time required to interpret the displays. CONCLUSIONS: The improvement in observer accuracy obtained from radiographs displayed in three dimensions results from an imaging strategy that selectively increases the signal-to-noise ratio in regions of interest.