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Figure 2a. US images of the gallbladder-with-stone phantom. (a) Representative directly scanned US image obtained by scanning perpendicular to the top edge of the phantom (top of image). The following artifacts are seen: stone shadowing (s), increased through-transmission (t), and refractile artifact (r). The thick white line indicates the plane of the reconstructed image in b, and the thin white line denoted with the curved arrow indicates the plane of the reconstructed image in d. (b) Coronal US image reconstructed in the plane of the thick white line in a. cf = simulated gallbladder fluid, r = refractile artifact, s = stone shadowing, St = the edge of the stone, t = area of through-transmission. (c) Directly scanned coronal US image obtained in the same plane as b (scan was obtained perpendicular to the right edge of the phantom in a by using the same machine settings for technical factors as those used for obtaining the 3D data set). The following differences are noted between this image and that in b: (a) On the direct coronal image, only the near edge of the stone is seen, as typically happens in vivo. On the coronal reconstruction (b), however, the entire stone periphery is seen. (b) In the direct coronal scan, the stone shadow obscures the far edge of the stone and the portions of the simulated gallbladder wall and phantom internal to the stone. In the coronal reconstruction, the shadow is reconstructed into the center of the stone as it shines down from above (the original direction of insonation, perpendicular to the plane of the reconstructed image) and does not obscure any portions of the simulated gallbladder wall or adjacent phantom. The stone shadow projected into the center of the stone gives the impression that the internal contents of the stone are hypoechoic, when, in fact, the hypoechoic appearance is entirely artifactual and is produced by the stone shadow alone. (c) In the coronal reconstruction, the increased through-transmission and the refractile artifact surround the simulated gallbladder fluid like the rings of Saturn because they are cast into the plane of reconstruction from above, just as with the shadowing from the stone. These artifacts project distal to the simulated gallbladder with direct scanning. r = refractile artifact, s = stone shadowing, St = edge of stone. (d) Coronal US image reconstructed in the plane of the thin white line denoted by the curved arrow in a. An echogenic target lesion is simulated in the coronal reconstructed image at this level. In vivo, this might be misinterpreted as a lesion of importance if the source of the artifacts was not appreciated. This appearance, however, is entirely due to artifacts cast into the reconstruction plane. A direct coronal scan through this area (not shown) only demonstrated the homogeneous speckle of the phantom substrate. r = refractile artifact, s = stone shadow, t = area of through-transmission.