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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
"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