High resolution graphic export from Keynote 09

I have a very high resolution image file that I have worked on in Keynote, and am losing resolution with all of the "best" export options I have tried (pdf, tiff, ppt and even .mov). I put a lot of time in here, and hate to go back to the drawing board. I have to get it into a more "standard" format for journal submission--e.g. tiff or pdf. Any suggestions on how to get the maximum resolution on export of a single slide? Thanks!