CT-based proton therapy dose calculation suffers from significant uncertainties that critically limit clinical efficacy. Previous works demonstrated improved proton range calculation by combining quantitative MRI with CT. This study extends those works into bone, a challenging region for tissue characterization. CT and a novel UTE MRI technique were used to investigate their complimentary information for bone characterization. Both phantom and in vivo experiments showed that combining UTE-MRI and CT measurements achieved accurate classification of bone types. Understanding of bone types can have significant implications on the determination of bone tissue composition and, ultimately, accuracy of radiation delivery in proton therapy.