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Dentomaxillofacial Radiology, Vol 31, Issue 4 249-256, Copyright © 2002 by British Institute of Radiology

ARTICLES

Implementation of a generalized TACT algorithm for arbitrary source-object distances

N. I. Linnenbrugger, R. L. Webber and T. M. Lehmann
Department of Dentistry, Wake Forest University School of Medicine, Winston-Salem, North Carolina, USA. nilin@web.de

OBJECTIVES: To implement, refine, and evaluate a generalized TACT reconstruction method that corrects for misregistration caused by uncontrolled variations in projective magnification, alleviates normalization artifacts at borders of backprojections, and exploits all available source information to minimize losses produced from projective truncations in three dimensions. METHODS: A new Java-based software application was designed and tested in vitro using clinically representive data derived from four titanium dental implants in a cadaver jaw segment. These implants were irradiated by an intra-oral X-ray machine from various angles and distances using a solid-state sensor producing 48 radiographs. Six radiopaque markers were attached to the segment facilitating inference of associated projection geometries from analyses of the distributions of their respective shadows as seen by the sensor. Three-dimensional (3D) images were produced using the new algorithm, and the results were compared with those obtained from existing code. RESULTS: Slices processed using the new program were corrected for magnification errors. The resulting 3D displays showed significantly reduced tomosynthetic blur relative to uncorrected counterparts. The new reconstructions also minimized known border artifacts and made use of all available information. These images demonstrated apparent details otherwise hidden or lost when comparably processed using the control algorithm. CONCLUSIONS: The new software reduces both misregistration and scaling artifacts in tomosynthetically reconstructed slices. Hence, these modifications are expected to increase diagnostic accuracy and facilitate the appropriate application of TACT to an enlarged set of diagnostic tasks as compared with earlier implementations of the method.




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