Advantages of subharmonic over second harmonic backscatter for contrast-to-tissue echo enhancement.

It is shown experimentally that backscatter from two ultrasonic contrast agents suspended in water or saline contains subharmonics of the incident frequency that are stronger than those backscattered at the same incident pressure from chicken breast. It is also shown that the ratio of subharmonic backscattered from contrast to that backscattered from tissue, is stronger than the ratio of backscattered second harmonic. In consequence, blood that contains contrast should be more easily detectable with respect to tissue if the subharmonic, rather than the second harmonic, is used for imaging.