3D compounding of B-scan ultrasound images

Ultrasound imaging compounded from different look directions can significantly decrease speckle noise and increase structural contrast. In addition, current limits on the field of view from small aperture scanheads can be overcome by combining two or more sets of partially overlapping 3D scan volumes into one super-volume by spatially coregistering the overlapping portions. The purpose of this study was to demonstrate both of these compound imaging enhancements. A 1.5-D linear array was used to obtain overlapping ultrasound volumes in phantoms and test subjects, reconstructed from at least 60 parallel B-scan planes for each volume. In the cases where independent look directions were required, either the transducer was tilted or the scan direction was changed. In all cases, the overlapping volumes were coregistered using an automated procedure based on a mutual information (MI) metric. The algorithm accounts for different look directions and/or tissue motion by geometrically transforming one volume set such that the MI of its overlap with the other is maximized, which leads to good structural overlap. The accuracy and stability of the MI algorithm demonstrate the feasibility of both compounding methods, offering increased lesion contrast and 3D fields of view larger than those from any currently available ultrasound imaging systems.