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Metal And Artifacts

“ Multidetector computed tomography is an excellent way to supplement the radiographic evaluation of problematic hip prosthesis.”
CT of the Hip Prosthesis: Appearance of Components, fixation, and Complications
Roth TD et al.
RadioGraphics 2012; 32:1089-1107
Factors Affecting Metal Artifacts at Multidetector CT
- Hardware related
- Scanner parameter related
CT of the Hip Prosthesis: Appearance of Components, fixation, and Complications
Roth TD et al.
RadioGraphics 2012; 32:1089-1107
Factors Affecting Metal Artifacts at Multidetector CT
- Hardware Related
- Composition
- Cobalt chrome based has highest photon attenuation
- Iron based (stainless steel) has high photon attenuation
- Titanium based has lower photon attenuation
Factors Affecting Metal Artifacts at Multidetector CT
- Hardware Related
- Geometry
- Shape-artifact greater with complex shapes
- Orientation-artifact greatest along the long axis in the axial plane
Factors Affecting Metal Artifacts at Multidetector CT
- Scanner Related Parameters
- Collimation-narrower collimation decreases artifacts
- Kilovolt peak-higher kVP reduces noise but lowers image contrast and increases radiation dose
- Milliampere seconds-higher mAs reduces noise but increases radiation dose
Factors Affecting Metal Artifacts at Multidetector CT
- Scanner Related Parameters (cont)
- Pitch-low pitch oversamples data, decreases artifact, and improves image quality but increases dose
- Reconstruction Algorithm-lower spatial frequency algorithms “smooth” the images and mitigate fine streaks around hardware
- Reconstruction Section Thickness-thicker sections decrease artifacts by averaging signal
Factors Affecting Metal Artifacts at Multidetector CT
- The use of 3D imaging with volume rendering and color coded mapping help provide quality imaging as compared to axial or multiplanar images alone
Value of 3D CT in defining skeletal complications of orthopedic hardware in the postoperative patient
Fayed LM, Patra A, Fishman EK
AJR 2009 Oct;193(4):1155-63
OBJECTIVE: Conventional CT of the postoperative patient with metal hardware is frequently limited by beam-hardening artifacts. With the evolution of 3D CT, CT is an increasingly effective means of examining the postsurgical patient for the integrity of their hardware and the course of their healing.
CONCLUSION: Potential postsurgical complications such as nonunion, osteolysis, infection, and heterotopic ossification are all well assessed by 3D CT.
Value of 3D CT in defining skeletal complications of orthopedic hardware in the postoperative patient
Fayed LM, Patra A, Fishman EK
AJR 2009 Oct;193(4):1155-63
Complications of Hip Prosthesis: CT Evaluation
- Dislocation and subluxation
- Component wear and frank hardware failure
- Osteolysis
- Periprosthetic fracture
- Soft tissue fluid collections
- Heterotopic ossification
“Use of the orthopedic MAR algorithm significantly reduces metal artifacts in CT of both phantoms and patients and has potential for improving diagnostic performance in patients with severe metallic artifacts.”

Usefulness of a Metal Artifact Reduction Algorithm for Orthopedic Implants in Abdominal CT: Phantom and Clinical Study Results 
Jeong S et al.
AJR 2015; 204:307–317 
“In the phantom study, the mean SD with orthopedic MAR was significantly lower than that without orthopedic MAR regardless of dose settings and reconstruction algorithms (FBP versus iterative reconstruction). The mean SD near the metallic prosthesis in 52 patients was significantly lower on CT images with orthopedic MAR (28.04 HU) than those without it (49.21 HU). Image quality regarding metallic artifact was significantly improved with orthopedic MAR (rating of 2.60 versus 1.04). Notable reduction of metallic artifacts and better depiction of abdominal organs were observed in 45 patients. Diagnostic benefit was achieved in six patients, but orthopedic MAR–related new artifacts were seen in 30 patients.”

Usefulness of a Metal Artifact Reduction Algorithm for Orthopedic Implants in Abdominal CT: Phantom and Clinical Study Results
Jeong S et al.
AJR 2015; 204:307–317 
“Strategies to reduce metallic artifacts in CT are various: increasing the tube voltage and tube current, application of an extended CT scale, thin-section collimation, small FOV, and application of dedicated reconstruction kernels. More elaborate metal artifact reduction (MAR) strategies are monoenergetic or spectral processing of dual-energy CT data , projection-interpolation methods , and iterative, statistical,and filtering methods . Monoenergetic or spectral processing of dual-energy CT data requires dedicated state-of-the-art dual-energy CT scanner hardware, which is not widely available.”

Usefulness of a Metal Artifact Reduction Algorithm for Orthopedic Implants in Abdominal CT: Phantom and Clinical Study Results
Jeong S et al.
AJR 2015; 204:307–317 
“Use of the O-MAR algorithm significantly reduces metal artifacts in CT in both phantom and clinical cases. It can also improve diagnostic performance in the evaluation of patients with severe metallic artifacts and decrease false-negative and false-positive rates. The review of O-MAR images cross-referenced with uncorrected images revealed additional information on the presence of metal implants.”

Usefulness of a Metal Artifact Reduction Algorithm for Orthopedic Implants in Abdominal CT: Phantom and Clinical Study Results
Jeong S et al.
AJR 2015; 204:307–317 
"In practice, the results of our study indicate that increasing kilovoltage is more effective for metal artifact reduction than increasing the effective mAs."
Metal Artifact Reduction by the Alteration of Technical Factors in Multidetector Computed Tomography: A 3-Dimensional Quantitative Assessment
Moon SG et al
J Comput Assist Tomogr 2008:32:630-633