Most of the top tier cardiology programs will give you good training in imaging. One caveat is that institutions with very strong radiology departments often have weaker imaging programs in cardiology. You want to be reading with cardiologists, not radiologits 🙂. From my interview experiences, programs that particularly stand out in my mind as strong in imaging are:
UCLA-Harbor (Cardiac CT)
Duke (Cardiac MR)
Hopkins
Spectacular programs but where radiology largely owns imaging -
UCSF
MGH (echo is very strong though)
WashU
By no means inclusive, and of course opinions will differ.