This article was originally published in Vol. 17 of the Journal of Biomedical Optics on 8 March 2012 in the wrong section of the table of contents and with an incorrect citation identifier (CID) of 036001. The paper was removed and republished online with the correct CID of 030506 on 19 March 2012. This change was made in order for the paper to appear under the correct section heading, “JBO Letters.”

For more information on the use of CIDs in JBO, see http://spiedigitallibrary.org/jbo/citation_format