No particular major will impress medical school admissions officers. Applicants with a huge variety of majors are admitted to medical schools every year. Adcomms have seen it all – everything from accounting to zoology.
What impresses adcomm is a high GPA/sGPA, a high MCAT score and exceptional ECs.
Major in a field you enjoy (because it’ll be easier to earn the high GPA needed for med schools admissions) and one that will provide you an alternate career should you change your mind about med school or should you not gain admission to med school.
Radiology is a specialty you will apply for during your last year of med school. While 99% of med students who apply to radiology match, the USMLE scores needed to match in radiology are quite high (as high as orthopedic surgeons or neurosurgeons).
Radiology requires an additional 5+ years of training after med school.
http://residency.wustl.edu/Choosing/SpecDesc/Pages/DiagnosticRadiology.aspx