I have done some work in before and after shots, as well as in developing surgical planning software for this field. If you are after medical documentary images a ring flash is a good choice since it is going to provide reduced shadow in most instances. Of course this is going to also affect the contrast and apparent surface detail since there won't be a lot of directional modeling light. For medical purposes that is almost allways fine. You will most likely also want a simple light background to create a neutral field for the subject. Perhaps Photek's People Popper (www.photek.usa.com
), or the Superlite backgrounds (www.superlitebackdrops.com
). You will want to be sure the color balance is well corrected for any lightsource since skin color changes are critical. You may want to use a small black/white/grey card or a mini-Macbeth in the shot, and most of the time you need a size reference scale in the shot as well. Try to establish some standard distances and positions for the subject and camera so shots are consistant. You will also want to consider patient privacy issues in light of HIPAA. Data in the file that ID's the patient may have to be controlled or restricted. Simple custom and decency also mandates blacking out portions of the image that can ID the patient in most cases.
If you need to light a larger area than your flash can accomodate well then consider using a light (strobe or color corrected florescent) behind a lite weight scrim pannel as a larger source. This sort of thing could be used as a room divider or moved out of the way when not needed. The beauty of in-place lighting or a ring light is that they are less imposing to the patient.