Effect of specular reflection on out-of-plane ultrasonographic images reconstructed from three-dimensional data sets

The effect of specular reflection on ultrasonographic images reconstructed out of plane to the plane of acquisition of a three-dimensional volumetric data set was studied using two in vitro phantoms that incorporated structur es exhibiting specular reflection. The phantoms were scanned transversely ( axially) to form three-dimensional data sets, with coronal cross-sectional images reconstructed perpendicular to the plane of acquisition of the ata s ets. Directly scanned, nonreconstructed coronal images of the phantoms also were obtained in the same planes and from the same areas as the reconstruc ted coronal images. The direct and reconstructed coronal images were compar ed. Owing to the inherent directionality of specular reflectors, the recons tructed coronal images differed from the directly scanned images in two way s, containing some hyperechoic regions that were not present at direct coro nal scanning and failing to contain other hyperechoic areas that were prese nt at direct coronal imaging. We conclude that sonographic images reformatt ed from volumetric data sets may have a different appearance than images sc anned directly in the same plane, independent of other factors such as reso lution. This should be taken into account when such reformatted images are interpreted.