WATANUKI M., KISHIMOTO K. N., KOTAJIMA S., IWABUCHI S., and KOKUBUN S. “Effect of Low-Intensity Pulsed Ultrasound on Scaffold-Free Ectopic Bone Formation in Skeletal Muscle”. Upsala Journal of Medical Sciences, vol. 114, no. 4, Dec. 2009, pp. 242–248, doi:10.3109/03009730903226659.