Sending healthcare information like that is very tricky, since you have to meet the healthcare security and privacy laws in your country (HIPAA in America). You might be able to use something like PGP to encrypt the emails and this may fine legally (I'm not a lawyer though). Encryption implemented through this would be fairly good support in email clients, so it should work for most places you want to share data with. However, this is a very hard-to-use solution. I'd be better to not have to email PHI like that. You still have to worry about auditing access to the data, as well as access control.

What you really need is software that can enabled collaboration between two healthcare providers. This would give your organization a lot more power than what you currently have. This software would then handle the secure communication between the two health practices. It would also let you share this data in a much easier, standards-based way.

As a side note, I started a [Healthcare Industry Stack Exchange proposal](http://area51.stackexchange.com/proposals/41370/healthcare-industry?referrer=0FgbVsKaId7Z_15aCbzplg2) where this question would be perfect.