You might find IHE's paper on this of interest: http://www.ihe.net/Technical_Framework/upload/IHE_ITI_Whitepaper_Security_and_Privacy_2007_07_18.pdf
If you are interested in grid services for healthcare, perhaps also the caBIG security technology evaluation at: https://cabig.nci.nih.gov/workspaces/Architecture/Security_Tech_Eval_White_Paper David
