This article has been retracted at the request of the Editor-in-Chief. Please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). Reason: The authors have plagiarized part of a paper that had already appeared in Clin. Radiol., 59 (2004) 609-615, doi:10.1016/j.crad.2004.01.006. One of the conditions of submission of a paper for publication is that authors declare explicitly that their work is original and has not been copied from another article prepared by another group of authors. Re-use of any data should be appropriately cited. As such this article represents a severe abuse of the scientific publishing system. The scientific community takes a very strong view on this matter and we apologize to readers of the journal and the original authors that this was not detected during the submission process.