Hi Pascal,
Sounds like an interesting project. If you are considering using the most recent version of OpenACS it would be a good fit. Here are some starting points.
1. We certainly have registration and collecting data solutions. One interesting project you might want to look at is out of UCLA Medical School. http://med.openacs.org/xowiki/en/UCLA_Case_Studies It is a Package called PTracker and they use it tracking patients through medical protocols. It might be overkill for what you are doing but you'll probably find it interesting.
There are web services solutions for OpenACS, a couple different ones, you should read the forums and see which one will fit your needs.
2 and 3 - Posting individual patient results, you could either use dotFolio (perhaps overkill) or file storage with some custom permissions. Not sure what your requirements are for strong authentication. MGH uses LDAP to let users log in from thier internal network. Not sure if that would work for you, perhaps checking IP in addition to username and password or a random number generator? That will require some extension to the toolkit but shouldn't be too bad.
4. I'd start with one of the Room or Resource reservation packages and customize from there. There is one in CVS and again the same group at UCLA wrote one recently.
5. There is a ratings package you can use to manage the ratings. We would probably use Dynamic Types to collect the ultrasounds and the measurements. There is a wiki page on dynamic types here: https://openacs.org/xowiki/dynamic-types and a discussion of another medical site that uses dynamic types here: http://med.openacs.org/xowiki/en/Case_Studies
Are you looking to create a new system with OpenACS 5x or extend your current 3x system or create a new system and integrate it with your current 3x system?
Hope these answers help,
