There's no point in a combined program. NM from radiology is a pretty easy fellowship to get from what I hear. If you don't like radiology and just want to do NM you can apply to NM straight (it's only like 4 yrs i think). But that's a very risky gamble since you can't read any CT, US, MRI, etc. I hear you have to bank on trying to get an academic position for the most part since most Radiology groups wont absorb a pure NM guy