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A digital subtraction radiography scheme based on automatic multiresolution registration

¹ Institute of Communication and Computer Systems, National Technical University of Athens, Athens, Greece; ² Department of Oral and Maxillofacial Radiology, Faculty of Odontology, The Sahlgrenska Academy at Göteborg University, Göteborg, Sweden

*Correspondence to: George K Matsopoulos, 9, Iroon Polytechniou str, Zografos, 15780, Athens, Greece; Email: gmatso{at}esd.ece.ntua.gr

Received 11 February 2004; revised 30 August 2004; accepted 3 October 2004

Objectives: To establish a digital subtraction radiography scheme for aligning clinical in vivo radiographs based on the implementations of an automatic geometric registration method and a contrast correction technique.

Methods: Thirty-five pairs of in vivo dental radiographs from four clinical studies were used in this work. First, each image pair was automatically aligned by applying a multiresolution registration strategy using the affine transformation followed by the implementation of the projective transformation at full resolution. Then, a contrast correction technique was applied in order to produce subtraction radiographs and fused images for further clinical evaluation. The performance of the proposed registration method was assessed against a manual method based on the projective transformation.

Results: The qualitative assessment of the experiments based on visual inspection has shown advantageous performance of the proposed automatic registration method against the manual method. Furthermore, the quantitative analysis showed statistical difference in terms of the root mean square (RMS) error estimated over the whole images and specific regions of interest.

Conclusions: The proposed automatic geometric registration method is capable of aligning radiographs acquired with or without rigorous a priori standardization. The methodology is pixel-based and does not require the application of any segmentation process prior to alignment. The employed projective transformation provides a reliable model for registering intraoral radiographs. The implemented contrast correction technique sequentially applied provides subtraction radiographs and fused images for clinical evaluation regarding the evolution of a disease or the response to a therapeutic scheme.

Keywords: subtraction radiography; image registration; fusion; projective transformation; contrast correction

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