Finite amplitude distortion-based inhomogeneous pulse echoultrasonic imaging

摘要

Ultrasonic pulse echo imaging in inhomogeneous media suffers fromnsignificant lateral and contrast resolution losses due to the defocusingneffects of the inhomogeneities. The losses in lateral and contrastnresolution are associated with increases in the width of the mainbeamnand increases in sidelobe levels, respectively. These two forms ofnresolution loss represent significant hurdles to improving the clinicalnutility of biomedical ultrasonic imaging. A number of research effortsnare currently under way to investigate the defocusing effects of tissuenand to consider corrective measures. All of these efforts assume linearnpropagation, and base the image-formation process on the reception ofnthe transmitted pulse. A novel pulse echo imaging scheme in which thenimage is formed using the finite amplitude distortion components of thenreceived pulse is considered here. Alternatively, this could bendescribed as image formation using the nonlinearly-generated highernharmonics. In homogeneous beam propagations, it has been establishednthat the sidelobes of nonlinearly-generated higher harmonics are muchnlower than their linear counterparts. Computations considered herensuggest that this relationship also holds for the case of propagationsnthrough abdominal wall and breast wall tissue. These computations alsonsuggest that the lateral resolution limits imposed by abdominal wall andnbreast wall tissue are slightly smaller for nonlinearly-generated secondnharmonics than for their linear counterparts. The resulting potential ofnthese higher harmonics to improve image resolution is investigated