如何确定C＃上最后一次更改文件名的时间？

I have small utility that does some processing on a file and changes the file extension to .processed when it is finished. I also want to delete these old .processed files after "x" number of days. Is there a file attribute that tells you when a filename was last changed? I realize that I can add white space to the end of the file after processing, re-save it, and then get the "LastWriteTime" attribute, but I do not want touch the original file at all. Any ideas?I have small utility that does some processing