I did 2 years of anesthesiology before radiology. I got credit for my intern year and am coming into radiology as a PGY-2. I lost the time i put in as a pgy-2 anesthesiology resident, and the gap year I had between ending my pgy2 and starting as a pgy2 radiology resident. I spent the year doing a research fellowship focused on cancer imaging and getting some publications. From a strictly time perspective, it's not ideal, as I will have done 6 years of training vs. 5 if I had started in radiology, ( +/- with fellowship ), and lost a bit of time in the transition. Other than that, If it's what you want to do, go for it - but if you complete pediatrics, you may be meeting the cap for ACGME salary funding, which I think is 7 years...could be 8, not sure.