Physical and historical bases of biomedical applications of radiation force

Abstract

Radiation force is a universal phenomenon in any wave motion, electromagnetic or acoustic. Radiation force is produced by a change in the density of energy of the propagating wave. The concept of radiation pressure follows from Maxwell’s equations (1871), while the idea of electromagnetic wave (light) pressure can be traced back to Johannes Kepler (1619). Acoustic radiation force was first experimentally demonstrated by August Kundt (1874) and its physical bases were analyzed in classical works of Lord Rayleigh (1902), L. Brillouin, and P. Langevin. Until recently, main biomedical application of acoustic radiation force was in measuring acoustic power of therapeutic devices, but during the last 15 years it became one of the hottest areas of biomedical ultrasonics with numerous new applications ranging from acoustical tweezers, targeted drug and gene delivery, manipulating of cells in suspension, increasing the sensitivity of biosensors and immunochemical tests, assessing viscoelastic properties of fluids and biological tissue, and monitoring lesions during therapy. The widest new area of applications of radiation force is related to medical imaging in general and elasticity imaging specifically. Remote excitation of shear stress in a given site in the body using radiation force of focused ultrasound offers numerous new possibilities for medical diagnostics.