Cardiac MR is definitely a niche, but a better one as far as radiology niches go.
Not all cardiac MR is practiced equally well, but if the institution does a good job with cardiac MR, it's a marker for the adequacy of the cardiothoracic division and a marker for the overall adequacy of MRI.
As a med student, you're not going to know how to evaluate the adequacy of an institution's cardiac MR division on your own:
- ask a senior resident in the program, preferably one going into a cardiothoracic fellowship. Ask the senior resident if he or she is comfortable reading cardiac MRI on his or her own. Which indications?
- ask what kinds of cases their referring clinicians send and how many (the larger the number and the more indications, the better). How many day a week is cardiac MRI read (every other week = poor, every day = good)
- ask how many rads read cardiac MRI. There will probably be one dominant person, but make sure there are more people reading it
- Cardiac MRI should be research-heavy. Ask what projects they are working on.
Cardiac is currently a large (disproportionate?) part of the core exam, so having more of this as a resident won't hurt you. Also, if you can protocol and troubleshoot a cardiac study, you can handle any MR situation.
Cardiac MRI is a valuable bonus for a program, but poor cardiac MRI (or lack of it) shouldn't be a strike against it.
Fellowship match list is more or less meaningless unless the residents stay at their own institution, which is a positive sign.