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US Artifacts: Effects on Out-of-Plane US Images Reconstructed from Three-dimensional Data Sets¹

¹ From the Department of Radiology, B1D 502, University of Michigan Medical Center, 1500 E Medical Center Dr, Ann Arbor, MI 48109-0030. Received December 3, 1999; revision requested January 21, 2000; revision received May 12; accepted June 1. Address correspondence to R.O.B. (e-mail: ronbude@umich.edu).

View larger version (125K): [in a new window]   Figure 1a. US images from the cyst phantom. (a) Representative directly scanned US image obtained by scanning perpendicular to the top edge of the phantom (top of image). A region of increased through-transmission (t), or distal acoustic enhancement, is present internal to the simulated cyst. Refractile shadowing (r) is seen at the lateral edges of the area of increased through-transmission. The thick white line indicates the plane of the reconstructed image in b, and the thin white line denoted by the curved arrow indicates the plane of the reconstructed image in c. (b) Coronal US image of the simulated cyst reconstructed from the 3D data set in the plane indicated by the thick white line in a. (c) Coronal US image reconstructed in the plane indicated by the thin white line in a. The increased through-transmission (t) manifests as an oval area of increased echogenicity produced by the simulated cyst in a, and this oval area is surrounded by the hypoechoic refractile artifact (r). The two regions are completely artifactual and were not present in direct coronal scans obtained in the same plane, which showed only the homogeneous speckle pattern of the phantom substrate. Note that in c, the artifacts mimic the appearance of an echogenic lesion with a hypoechoic halo. This appearance in vivo would simulate an echogenic mass.

View larger version (179K): [in a new window]   Figure 1b. US images from the cyst phantom. (a) Representative directly scanned US image obtained by scanning perpendicular to the top edge of the phantom (top of image). A region of increased through-transmission (t), or distal acoustic enhancement, is present internal to the simulated cyst. Refractile shadowing (r) is seen at the lateral edges of the area of increased through-transmission. The thick white line indicates the plane of the reconstructed image in b, and the thin white line denoted by the curved arrow indicates the plane of the reconstructed image in c. (b) Coronal US image of the simulated cyst reconstructed from the 3D data set in the plane indicated by the thick white line in a. (c) Coronal US image reconstructed in the plane indicated by the thin white line in a. The increased through-transmission (t) manifests as an oval area of increased echogenicity produced by the simulated cyst in a, and this oval area is surrounded by the hypoechoic refractile artifact (r). The two regions are completely artifactual and were not present in direct coronal scans obtained in the same plane, which showed only the homogeneous speckle pattern of the phantom substrate. Note that in c, the artifacts mimic the appearance of an echogenic lesion with a hypoechoic halo. This appearance in vivo would simulate an echogenic mass.

View larger version (175K): [in a new window]   Figure 1c. US images from the cyst phantom. (a) Representative directly scanned US image obtained by scanning perpendicular to the top edge of the phantom (top of image). A region of increased through-transmission (t), or distal acoustic enhancement, is present internal to the simulated cyst. Refractile shadowing (r) is seen at the lateral edges of the area of increased through-transmission. The thick white line indicates the plane of the reconstructed image in b, and the thin white line denoted by the curved arrow indicates the plane of the reconstructed image in c. (b) Coronal US image of the simulated cyst reconstructed from the 3D data set in the plane indicated by the thick white line in a. (c) Coronal US image reconstructed in the plane indicated by the thin white line in a. The increased through-transmission (t) manifests as an oval area of increased echogenicity produced by the simulated cyst in a, and this oval area is surrounded by the hypoechoic refractile artifact (r). The two regions are completely artifactual and were not present in direct coronal scans obtained in the same plane, which showed only the homogeneous speckle pattern of the phantom substrate. Note that in c, the artifacts mimic the appearance of an echogenic lesion with a hypoechoic halo. This appearance in vivo would simulate an echogenic mass.

View larger version (153K): [in a new window]   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.

View larger version (179K): [in a new window]   Figure 2b. 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.

View larger version (157K): [in a new window]   Figure 2c. 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.

View larger version (183K): [in a new window]   Figure 2d. 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.

View larger version (162K): [in a new window]   Figure 3a. In vivo US images of a forearm dialysis fistula. (a) Representative directly scanned US image from the 3D data set shows a transverse cross-section of the fistula (f), with scanning performed perpendicular to the top of the image. A refractile artifact (r) is seen to arise from the edges of the fistula. The white line at top indicates the plane of the reconstructed image in b, and the white line denoted with the curved arrow indicates the plane of the reconstructed image in c. (b) Coronal US image of the fistula (arrowheads), reconstructed as if scanned perpendicular to the right side of the image in a at the level of the white line, demonstrates the curved course of the fistula through the forearm. (c) Coronal US image reconstructed at the level of the white line denoted with the curved arrow in a, but deeper into the soft tissues than in b, so that the reconstructed image includes only the refractile artifacts (r) (the two concentric hypoechoic rings) and does not contain any portion of the fistula. These concentric hypoechoic rings would not be present on a directly scanned coronal image (not obtained in this case because of the difficulties imposed on direct scanning by the geometry of the forearm).

View larger version (108K): [in a new window]   Figure 3b. In vivo US images of a forearm dialysis fistula. (a) Representative directly scanned US image from the 3D data set shows a transverse cross-section of the fistula (f), with scanning performed perpendicular to the top of the image. A refractile artifact (r) is seen to arise from the edges of the fistula. The white line at top indicates the plane of the reconstructed image in b, and the white line denoted with the curved arrow indicates the plane of the reconstructed image in c. (b) Coronal US image of the fistula (arrowheads), reconstructed as if scanned perpendicular to the right side of the image in a at the level of the white line, demonstrates the curved course of the fistula through the forearm. (c) Coronal US image reconstructed at the level of the white line denoted with the curved arrow in a, but deeper into the soft tissues than in b, so that the reconstructed image includes only the refractile artifacts (r) (the two concentric hypoechoic rings) and does not contain any portion of the fistula. These concentric hypoechoic rings would not be present on a directly scanned coronal image (not obtained in this case because of the difficulties imposed on direct scanning by the geometry of the forearm).

View larger version (120K): [in a new window]   Figure 3c. In vivo US images of a forearm dialysis fistula. (a) Representative directly scanned US image from the 3D data set shows a transverse cross-section of the fistula (f), with scanning performed perpendicular to the top of the image. A refractile artifact (r) is seen to arise from the edges of the fistula. The white line at top indicates the plane of the reconstructed image in b, and the white line denoted with the curved arrow indicates the plane of the reconstructed image in c. (b) Coronal US image of the fistula (arrowheads), reconstructed as if scanned perpendicular to the right side of the image in a at the level of the white line, demonstrates the curved course of the fistula through the forearm. (c) Coronal US image reconstructed at the level of the white line denoted with the curved arrow in a, but deeper into the soft tissues than in b, so that the reconstructed image includes only the refractile artifacts (r) (the two concentric hypoechoic rings) and does not contain any portion of the fistula. These concentric hypoechoic rings would not be present on a directly scanned coronal image (not obtained in this case because of the difficulties imposed on direct scanning by the geometry of the forearm).

View larger version (138K): [in a new window]   Figure 4a. In vivo US images of a liver cyst. (a) Directly scanned US image of a liver cyst (arrow) shows a well-defined band of distal acoustic enhancement (arrowheads) deep to the cyst. (b) US image of the midportion of the liver cyst (arrows), reconstructed from the 3D data set in the coronal plane, orthogonal to the plane in which a was acquired. (c) US image of liver parenchyma deep to the cyst, reconstructed from the 3D data set in a coronal plane parallel to that in b. Note the rounded area of increased echogenicity (arrows) compared to adjacent liver parenchyma that is due to inclusion of distal acoustic enhancement artifact in the reconstructed image. This artifact has the potential to simulate an echogenic liver mass such as a hemangioma or echogenic metastasis.

View larger version (149K): [in a new window]   Figure 4b. In vivo US images of a liver cyst. (a) Directly scanned US image of a liver cyst (arrow) shows a well-defined band of distal acoustic enhancement (arrowheads) deep to the cyst. (b) US image of the midportion of the liver cyst (arrows), reconstructed from the 3D data set in the coronal plane, orthogonal to the plane in which a was acquired. (c) US image of liver parenchyma deep to the cyst, reconstructed from the 3D data set in a coronal plane parallel to that in b. Note the rounded area of increased echogenicity (arrows) compared to adjacent liver parenchyma that is due to inclusion of distal acoustic enhancement artifact in the reconstructed image. This artifact has the potential to simulate an echogenic liver mass such as a hemangioma or echogenic metastasis.

View larger version (147K): [in a new window]   Figure 4c. In vivo US images of a liver cyst. (a) Directly scanned US image of a liver cyst (arrow) shows a well-defined band of distal acoustic enhancement (arrowheads) deep to the cyst. (b) US image of the midportion of the liver cyst (arrows), reconstructed from the 3D data set in the coronal plane, orthogonal to the plane in which a was acquired. (c) US image of liver parenchyma deep to the cyst, reconstructed from the 3D data set in a coronal plane parallel to that in b. Note the rounded area of increased echogenicity (arrows) compared to adjacent liver parenchyma that is due to inclusion of distal acoustic enhancement artifact in the reconstructed image. This artifact has the potential to simulate an echogenic liver mass such as a hemangioma or echogenic metastasis.