DaisyMay,
We need a little more information. First if you could find out what type of files are loaded onto the CD, are the images saved in a propriatary file format (this is a major pain if so), or something more standard like jpg, tiff, etc..
You can run MS Windows on your Mac, that's the good news. If you do you will need to get a license of MS Windows either XP, Vista or Windows 7. Then you will need to decide how you want to run it. You can dual boot your iMac as either a Mac or PC using Boot Camp, Boot Camp is already loaded on your machine. The up side is it's already included the down side is you can either run in MS Windows or OS X but you can't run them simultaneously.
For your needs I'd recommend either Parallels or VM Ware Fusion. Both are excellent and allow you to run MS Windows and OS X simultaneously. Personally I use Fusion and have found it to be stable and pretty fast, other like Parallels just as much. In addition there is free software that will do the same thing however unless you consider yourself very OS savvy and technical I'd recommend Fusion or Parallels.
My recommendation is to ask your hospital personnel if they can save the images in a more standard format like JPG or TIFF, if they can then reading them should be extremely simple and you can avoid the whole MS Windows experience. If they are in
any of the formats supported by Preview (Applications-Preview) you're in business!
If you do decide to load MS Windows on your Mac in any fashion remember that part of your machine will be susceptible to all the oddities Windows users suffer from including virus's and other malware. So if you do decide to load Windows take proper precautions. The good news is even if the Windows portion becomes diseased it in now way affections the OS X partion.
Roger