Changes of vocal tract shape accompanying changes of vocal register and pitch in singing have remained an unclear field. Dynamic real-time magnetic resonance imaging (MRI) was applied to two professional classical singers (a tenor and a baritone) in this pilot study. The singers sang ascending scales from B3 to G#4 on the vowel /a/, keeping the modal register throughout or shifting to falsetto register for the highest pitches. The results show that these singers made few and minor modifications of vocal tract shape when they changed from modal to falsetto and some clear modifications when they kept the register. In this case the baritone increased his tongue dorsum height, widened his jaw opening, and decreased his jaw protrusion, while the tenor merely lifted his uvula. The method used seems promising and should be applied to a greater number of singer subjects in the future.