My interest in radiology began when I was a little child and the radiologists diagnosis saved my life. Oh, sorry, thats for a medicine essay.
I liked radiology as a first year in anatomy and got a chance to do some research in fMRI and my interest grew. I got to go down to radiology and review films during all of my rotations and loved it. I was still thinking about doing medicine followed by cardiology mid way through my thrid year (and after my intern year in medicine, thank god I didn't do that). I did a two week elective in third year and loved rads. When on the rotation, you have to put yourself in the place of the residents and attendings instead of judging it based on what you do as a student, since that is basically nothing. I then did a month long rotation early in 4th year and that confirmed it.
Its a great specialty. Its high tech, much more relaxed than most other specialties (as Cuts pointed out), endlessly interesting (you get to see the diagnoses of every specialty and learn multiple modalities of imaging), and you make a great income. What could be better.