This article [ J. Biomed. Opt. 13, 024015 (2008)] was originally published online 23 April 2008 with an error in the corresponding author contact information. Jianan Y. Qu was not listed as a corresponding author. The footnote on page 1 has been changed to: ${}^{*}$ Address all correspondence to Min Xu, E-mail: mxu@mail.fairfield.edu; and Jianan Y. Qu, E-mail: eequ@ust.hk. All online versions of the article were corrected on 29 April 2008. The article appears correctly in print.