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Artifacts at PET and PET/CT Caused by Metallic Hip Prosthetic Material¹

¹ From the Division of Nuclear Medicine, University Hospital Zurich, Rämistrasse 100, CH-8091 Zurich, Switzerland (G.W.G., C.B., T.B., G.K.v.S., A.B.); and Nuclear Medicine Clinics, Technischen Universität München, Munich, Germany (S.I.Z.). Received January 9, 2002; revision requested March 4; revision received May 1; accepted June 5. G.W.G. supported by an award from the Research and Education Fund of the European Association of Radiology. Address correspondence to G.W.G. (e-mail: gerhard.goerres@dmr.usz.ch).

View larger version (53K): [in a new window]   Figure 1. Prostheses from two different manufacturers were scanned. Two (Sulzer Medica) consisted of a femoral stem and the corresponding acetabular component: A, the Allo Pro Ti-Al-Nb 920206-4 titanium; and B, the Allo Pro A 907 257 steel. Four femoral stems (Stratec Medical) with different shapes and surface properties were also measured: C, Proxilock FT Mat 190 5832-3 titanium; D, Manistream Müller Mat 190 5832-9 steel; E, Manistream 30 Mat 130 5832-9 steel; F, PPF Mat 5832-3 titanium. G, A steel rod with a circular cross-sectional profile (diameter, 4 cm) was also scanned.

View larger version (80K): [in a new window]   Figure 2. Coronal PET images of the prosthesis shown in Figure 1, B, in an FDG water bath. A, Non-attenuation-corrected PET image reconstructed with FBP (from a 4-minute emission scan) shows an artifact located within the prosthetic material itself. The activity profile below the PET image, obtained along the horizontal line in the PET image, shows the measured radioactivity concentration in relation to the background in the water tank. B, PET image obtained after AC was applied with the 68Ge sources (during a 4-minute transmission scan) that was reconstructed with segmentation shows that artifact has been generated adjacent to the metallic implant. Artifact is evident in areas with steep differences in attenuation values between the metal and the surrounding water—for example, the shoulder of the prosthesis (long arrow) or the anterior and posterior surfaces (short arrows) of the prosthesis, which have an uneven shape. The activity profile, obtained along the horizontal line in the PET image, shows that the measured FDG concentration in the artifact is approximately twice that of the water basin. C, On a PET image obtained after AC was applied (during a 4-minute emission scan) and with IR, no artifacts are visible. D, On a PET image obtained after 68Ge-based AC was applied and with IR, artifact (arrows) due to partial volume mapping is seen adjacent to the metal. The activity profile, obtained along the horizontal line in the PET image, shows that the measured FDG concentration is about twice that of the surrounding water. E, PET image obtained with the ECAT Exact HR+ scanner also shows artifact (arrows), underlining the fact that the generation of these artifacts is an inherent problem of AC. However, artifact is less marked on this image; this is due to the different method of image reconstruction (ie, an attenuation-weighted IR algorithm) used with this scanner.

View larger version (53K): [in a new window]   Figure 3a. PET images of the steel rod phantom. (a) On images obtained with 4-minute emission scan and 180-minute transmission scan and reconstructed with segmentation and IR, a black circlelike artifact is visible around the steel rod in the large water basin. With longer-duration conventional transmission scan, image noise is reduced and artifact is somewhat more visible (see c). (b) On images from 4-minute emission scan with CT-based AC and IR, absorption of photons by the water tank has created inhomogeneities in the attenuation map that have influenced the appearance of artifacts adjacent to the metal. (c) Images obtained with 4-minute emission scan and 4-minute transmission scan and reconstructed with IR shows that repositioning of the steel rod within the water tank did not affect artifacts generated with conventional AC. (d) Images from the corresponding 68Ge-based transmission scan illustrates quality of attenuation map. (e) In contrast to c, these images show that repositioning of the steel rod within the water basin led to a change in artifact appearance when CT-based AC was used. Therefore, it can be expected that attenuation properties in a patient will be more important when CT-based AC is used. (f) Images from the corresponding transmission scan (40 mAs) with CT-based AC show that CT-based AC creates a high-quality attenuation map with less noise. However, adjacent to the metal is an artifact (arrows) with a spiral-like appearance. In addition, the absorption of photons in the water tank has created inhomogeneities in the attenuation map that are visible as white stripes. They influenced artifact appearance on the final reconstructed PET image in e. (g) Images obtained with a 4-minute emission scan and a 2-minute transmission scan and reconstructed with segmentation before (left) and after (right) rotation of the hip prosthesis show that rotation of the item within the same coronal plane has changed the position of the artifact (arrows) along the hip prosthesis because the geometric relationship between the radiation source and the steep edges of the prosthesis has changed. These images are set at a very dark gray-scale level to show that after rotation, the artifact is more visible at the shoulder of the prosthesis than at the femoral shaft.

View larger version (57K): [in a new window]   Figure 3b. PET images of the steel rod phantom. (a) On images obtained with 4-minute emission scan and 180-minute transmission scan and reconstructed with segmentation and IR, a black circlelike artifact is visible around the steel rod in the large water basin. With longer-duration conventional transmission scan, image noise is reduced and artifact is somewhat more visible (see c). (b) On images from 4-minute emission scan with CT-based AC and IR, absorption of photons by the water tank has created inhomogeneities in the attenuation map that have influenced the appearance of artifacts adjacent to the metal. (c) Images obtained with 4-minute emission scan and 4-minute transmission scan and reconstructed with IR shows that repositioning of the steel rod within the water tank did not affect artifacts generated with conventional AC. (d) Images from the corresponding 68Ge-based transmission scan illustrates quality of attenuation map. (e) In contrast to c, these images show that repositioning of the steel rod within the water basin led to a change in artifact appearance when CT-based AC was used. Therefore, it can be expected that attenuation properties in a patient will be more important when CT-based AC is used. (f) Images from the corresponding transmission scan (40 mAs) with CT-based AC show that CT-based AC creates a high-quality attenuation map with less noise. However, adjacent to the metal is an artifact (arrows) with a spiral-like appearance. In addition, the absorption of photons in the water tank has created inhomogeneities in the attenuation map that are visible as white stripes. They influenced artifact appearance on the final reconstructed PET image in e. (g) Images obtained with a 4-minute emission scan and a 2-minute transmission scan and reconstructed with segmentation before (left) and after (right) rotation of the hip prosthesis show that rotation of the item within the same coronal plane has changed the position of the artifact (arrows) along the hip prosthesis because the geometric relationship between the radiation source and the steep edges of the prosthesis has changed. These images are set at a very dark gray-scale level to show that after rotation, the artifact is more visible at the shoulder of the prosthesis than at the femoral shaft.

View larger version (54K): [in a new window]   Figure 3c. PET images of the steel rod phantom. (a) On images obtained with 4-minute emission scan and 180-minute transmission scan and reconstructed with segmentation and IR, a black circlelike artifact is visible around the steel rod in the large water basin. With longer-duration conventional transmission scan, image noise is reduced and artifact is somewhat more visible (see c). (b) On images from 4-minute emission scan with CT-based AC and IR, absorption of photons by the water tank has created inhomogeneities in the attenuation map that have influenced the appearance of artifacts adjacent to the metal. (c) Images obtained with 4-minute emission scan and 4-minute transmission scan and reconstructed with IR shows that repositioning of the steel rod within the water tank did not affect artifacts generated with conventional AC. (d) Images from the corresponding 68Ge-based transmission scan illustrates quality of attenuation map. (e) In contrast to c, these images show that repositioning of the steel rod within the water basin led to a change in artifact appearance when CT-based AC was used. Therefore, it can be expected that attenuation properties in a patient will be more important when CT-based AC is used. (f) Images from the corresponding transmission scan (40 mAs) with CT-based AC show that CT-based AC creates a high-quality attenuation map with less noise. However, adjacent to the metal is an artifact (arrows) with a spiral-like appearance. In addition, the absorption of photons in the water tank has created inhomogeneities in the attenuation map that are visible as white stripes. They influenced artifact appearance on the final reconstructed PET image in e. (g) Images obtained with a 4-minute emission scan and a 2-minute transmission scan and reconstructed with segmentation before (left) and after (right) rotation of the hip prosthesis show that rotation of the item within the same coronal plane has changed the position of the artifact (arrows) along the hip prosthesis because the geometric relationship between the radiation source and the steep edges of the prosthesis has changed. These images are set at a very dark gray-scale level to show that after rotation, the artifact is more visible at the shoulder of the prosthesis than at the femoral shaft.

View larger version (50K): [in a new window]   Figure 3d. PET images of the steel rod phantom. (a) On images obtained with 4-minute emission scan and 180-minute transmission scan and reconstructed with segmentation and IR, a black circlelike artifact is visible around the steel rod in the large water basin. With longer-duration conventional transmission scan, image noise is reduced and artifact is somewhat more visible (see c). (b) On images from 4-minute emission scan with CT-based AC and IR, absorption of photons by the water tank has created inhomogeneities in the attenuation map that have influenced the appearance of artifacts adjacent to the metal. (c) Images obtained with 4-minute emission scan and 4-minute transmission scan and reconstructed with IR shows that repositioning of the steel rod within the water tank did not affect artifacts generated with conventional AC. (d) Images from the corresponding 68Ge-based transmission scan illustrates quality of attenuation map. (e) In contrast to c, these images show that repositioning of the steel rod within the water basin led to a change in artifact appearance when CT-based AC was used. Therefore, it can be expected that attenuation properties in a patient will be more important when CT-based AC is used. (f) Images from the corresponding transmission scan (40 mAs) with CT-based AC show that CT-based AC creates a high-quality attenuation map with less noise. However, adjacent to the metal is an artifact (arrows) with a spiral-like appearance. In addition, the absorption of photons in the water tank has created inhomogeneities in the attenuation map that are visible as white stripes. They influenced artifact appearance on the final reconstructed PET image in e. (g) Images obtained with a 4-minute emission scan and a 2-minute transmission scan and reconstructed with segmentation before (left) and after (right) rotation of the hip prosthesis show that rotation of the item within the same coronal plane has changed the position of the artifact (arrows) along the hip prosthesis because the geometric relationship between the radiation source and the steep edges of the prosthesis has changed. These images are set at a very dark gray-scale level to show that after rotation, the artifact is more visible at the shoulder of the prosthesis than at the femoral shaft.

View larger version (41K): [in a new window]   Figure 3e. PET images of the steel rod phantom. (a) On images obtained with 4-minute emission scan and 180-minute transmission scan and reconstructed with segmentation and IR, a black circlelike artifact is visible around the steel rod in the large water basin. With longer-duration conventional transmission scan, image noise is reduced and artifact is somewhat more visible (see c). (b) On images from 4-minute emission scan with CT-based AC and IR, absorption of photons by the water tank has created inhomogeneities in the attenuation map that have influenced the appearance of artifacts adjacent to the metal. (c) Images obtained with 4-minute emission scan and 4-minute transmission scan and reconstructed with IR shows that repositioning of the steel rod within the water tank did not affect artifacts generated with conventional AC. (d) Images from the corresponding 68Ge-based transmission scan illustrates quality of attenuation map. (e) In contrast to c, these images show that repositioning of the steel rod within the water basin led to a change in artifact appearance when CT-based AC was used. Therefore, it can be expected that attenuation properties in a patient will be more important when CT-based AC is used. (f) Images from the corresponding transmission scan (40 mAs) with CT-based AC show that CT-based AC creates a high-quality attenuation map with less noise. However, adjacent to the metal is an artifact (arrows) with a spiral-like appearance. In addition, the absorption of photons in the water tank has created inhomogeneities in the attenuation map that are visible as white stripes. They influenced artifact appearance on the final reconstructed PET image in e. (g) Images obtained with a 4-minute emission scan and a 2-minute transmission scan and reconstructed with segmentation before (left) and after (right) rotation of the hip prosthesis show that rotation of the item within the same coronal plane has changed the position of the artifact (arrows) along the hip prosthesis because the geometric relationship between the radiation source and the steep edges of the prosthesis has changed. These images are set at a very dark gray-scale level to show that after rotation, the artifact is more visible at the shoulder of the prosthesis than at the femoral shaft.

View larger version (33K): [in a new window]   Figure 3f. PET images of the steel rod phantom. (a) On images obtained with 4-minute emission scan and 180-minute transmission scan and reconstructed with segmentation and IR, a black circlelike artifact is visible around the steel rod in the large water basin. With longer-duration conventional transmission scan, image noise is reduced and artifact is somewhat more visible (see c). (b) On images from 4-minute emission scan with CT-based AC and IR, absorption of photons by the water tank has created inhomogeneities in the attenuation map that have influenced the appearance of artifacts adjacent to the metal. (c) Images obtained with 4-minute emission scan and 4-minute transmission scan and reconstructed with IR shows that repositioning of the steel rod within the water tank did not affect artifacts generated with conventional AC. (d) Images from the corresponding 68Ge-based transmission scan illustrates quality of attenuation map. (e) In contrast to c, these images show that repositioning of the steel rod within the water basin led to a change in artifact appearance when CT-based AC was used. Therefore, it can be expected that attenuation properties in a patient will be more important when CT-based AC is used. (f) Images from the corresponding transmission scan (40 mAs) with CT-based AC show that CT-based AC creates a high-quality attenuation map with less noise. However, adjacent to the metal is an artifact (arrows) with a spiral-like appearance. In addition, the absorption of photons in the water tank has created inhomogeneities in the attenuation map that are visible as white stripes. They influenced artifact appearance on the final reconstructed PET image in e. (g) Images obtained with a 4-minute emission scan and a 2-minute transmission scan and reconstructed with segmentation before (left) and after (right) rotation of the hip prosthesis show that rotation of the item within the same coronal plane has changed the position of the artifact (arrows) along the hip prosthesis because the geometric relationship between the radiation source and the steep edges of the prosthesis has changed. These images are set at a very dark gray-scale level to show that after rotation, the artifact is more visible at the shoulder of the prosthesis than at the femoral shaft.

View larger version (72K): [in a new window]   Figure 3g. PET images of the steel rod phantom. (a) On images obtained with 4-minute emission scan and 180-minute transmission scan and reconstructed with segmentation and IR, a black circlelike artifact is visible around the steel rod in the large water basin. With longer-duration conventional transmission scan, image noise is reduced and artifact is somewhat more visible (see c). (b) On images from 4-minute emission scan with CT-based AC and IR, absorption of photons by the water tank has created inhomogeneities in the attenuation map that have influenced the appearance of artifacts adjacent to the metal. (c) Images obtained with 4-minute emission scan and 4-minute transmission scan and reconstructed with IR shows that repositioning of the steel rod within the water tank did not affect artifacts generated with conventional AC. (d) Images from the corresponding 68Ge-based transmission scan illustrates quality of attenuation map. (e) In contrast to c, these images show that repositioning of the steel rod within the water basin led to a change in artifact appearance when CT-based AC was used. Therefore, it can be expected that attenuation properties in a patient will be more important when CT-based AC is used. (f) Images from the corresponding transmission scan (40 mAs) with CT-based AC show that CT-based AC creates a high-quality attenuation map with less noise. However, adjacent to the metal is an artifact (arrows) with a spiral-like appearance. In addition, the absorption of photons in the water tank has created inhomogeneities in the attenuation map that are visible as white stripes. They influenced artifact appearance on the final reconstructed PET image in e. (g) Images obtained with a 4-minute emission scan and a 2-minute transmission scan and reconstructed with segmentation before (left) and after (right) rotation of the hip prosthesis show that rotation of the item within the same coronal plane has changed the position of the artifact (arrows) along the hip prosthesis because the geometric relationship between the radiation source and the steep edges of the prosthesis has changed. These images are set at a very dark gray-scale level to show that after rotation, the artifact is more visible at the shoulder of the prosthesis than at the femoral shaft.

View larger version (124K): [in a new window]   Figure 4. Coronal PET images illustrate the effect of repositioning the prosthesis 3 mm to the right between emission and transmission scanning, which was performed to mimic patient movement. Misalignment between emission scanning and the attenuation map creates a black stripe that is evident when a 4-minute emission scan, a 10-minute transmission scan, and IR and segmentation are used. Images obtained, A, before and, B, after the change of position show the increase in visibility of the artifact due to repositioning of the prosthesis. The same phenomenon is evident when CT-based AC is used on images obtained before (C) and after (D) the change of position. With CT-based AC, this artifact is slightly more evident (as seen in D compared with B). The artifact mimics increased FDG uptake adjacent to the femoral stem in this experiment, but it could have a more focal appearance depending on what movement is performed. The activity profiles show that measured radioactivity concentration is two to three times that of the surrounding water. (The left and right activity profiles were obtained at the levels of the horizontal lines in B and D, respectively.)