Medical applications which employ microbubbles, such as ultrasound imaging, gene transfer and sonodynamic therapy, are currently being investigated. In the field of bubble dynamics, it is known that bubbles can play a role in converting the mechanical energy of an ultrasound wave into not only energy of acoustic emission but also heat energy deposition when they are subjected to an oscillating field. In this study, the desired properties of the microbubble acting either as an echo source or a heat source are discussed. The type of gas inside a bubble has a strong effect on the energy radiation from the bubbles. It is shown that the balance between heat deposition and acoustic emission from the bubbles can be altered by changing the gas inside the bubbles. Consequently, HIFU treatment or ultrasound imaging can be carried out more effectively, utilizing these microbubbles.