Subharmonic imaging of contrast agents

Ultrasound contrast agents promise to improve the sensitivity and specifici ty of diagnostic ultrasound imaging. It is of great importance to adapt ult rasound equipment for optimal use with contrast agents e.g., by exploiting the nonlinear properties of the contrast microbubbles. Harmonic imaging is one technique that has been extensively studied and is commercially availab le. However, harmonic imaging is associated with problems, due to second ha rmonic generation and accumulation within the tissue itself. Given the lack of subharmonic generation in tissue, one alternative is the creation of su bharmonic images by transmitting at the fundamental frequency (f(o)) and re ceiving at the subharmonic (f(o)/2). Subharmonic imaging should have a much better lateral resolution and may be suitable for scanning deep-lying stru ctures owing to the higher transmit frequency and the much smaller attenuat ion of scattered subharmonic signals. Tn this paper, we will review differe nt aspects of subharmonic imaging including implementation, in-vitro gray-s cale imaging and subharmonic aided pressure estimation. (C) 2000 Elsevier S cience B.V. All rights reserved.