Harmonic US in hepatobiliary disease

Abstract

Harmonic ultrasound (US) is a new sonographic imaging method that exploits the effect of nonlinear propagation on the acoustic signal as it travels through the human body or tissue. It produces sonographic images by using second harmonic signals generated by tissue itself during this nonlinear propagation of insonated acoustic energy. The resultant advantages are improved lateral resolution, reduced side lobe artifact, and increased signal-to-noise ratio. Our recent clinical studies using tissue harmonic US showed that tissue harmonic US provided significantly better image quality in both solid and cystic hepatic structures than conventional imaging, and enabled significantly improved image quality and improved diagnostic accuracy in evaluation of gallbladder disease. Harmonic US enhances the signals from contrast over those from tissue, since the contrast agent microbubbles generate far more harmonic energy than tissue does. New promising contrast-enhanced US techniques are pulse inversion harmonic, coded harmonic angio (CHA), and agent detection imaging (ADI). CHA uses codes to suppress the fundamental signal, and uses decoding techniques optimized for contrast agents, to suppress tissue signal, thus, improving sensitivity and uniquely optimizing for contrast signal visualization in dynamic flow states. ADI is a microbubble-specific mode that is designed for optimal detection of stimulated acoustic emission from a fragile agent such as Levovist, and is characterized as its high mechanical index that provides extreme sensitivity to the presence of microbubble. Our recent clinical experience of contrast-enhanced harmonic US with Levovist will be presented in various diseases of hepatobiliary system.