New sonographic techniques for harmonic imaging--underlying physical principles.

In this paper, modern harmonic imaging techniques are reviewed and their physical principles are explained. The clinical advantages of these new techniques that are generally used in conjunction with ultrasound contrast agents are highlighted and compared to conventional flow imaging methods. Low/high mechanical index (MI) methods are discussed as well as emerging technologies for future transducer or beamformer generations. Finally the latest safety issues concerning applications of modern (harmonic) imaging techniques with contrast agents are given.