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  5. SOMATOM go.Top Experience with iMAR (iterative metal artifact reduction)

SOMATOM go.Top Experience with iMAR (iterative metal artifact reduction)Al Borg Scan Center, Cairo, Egypt

2019-05-01
SOMATOM go.Top Experience with iMAR (iterative metal artifact reduction)
The streak artifacts caused by metal implants have long been recognized as a problem that limits various applications of CT imaging. Metal artifacts can seriously degrade the quality of images. Sometimes metal artifacts produce images that are diagnostically worthless. To correct the image quality, it is necessary to understand why artifacts occur and how they can be prevented or suppressed.
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SOMATOM go.Top Experience with iMAR (iterative metal artifact reduction)
Figure 1A, 1B: Axial CT images obtained with ortho implant with screw.
(a)Metallic artifacts obscure large parts of soft tissue.
(b) iMAR reduces artifacts, with significantly improving image quality.
SOMATOM go.Top Experience with iMAR (iterative metal artifact reduction)
SOMATOM go.Top Experience with iMAR (iterative metal artifact reduction)
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In physics, the metal artifacts derive from the dark shadows in the calculated sinogram due to the high attenuation of the metal objects when x-rays pass through them. It is called photon starvation and beam hardening. These “high attenuation umbra” provides insufficient information for image reconstruction. The solution is to retrieve the “lost information from the sinogram” and this is the soul of metal artifacts removal in image reconstruction.
SOMATOM go.Top Experience with iMAR
Figure 3: MPR CT images obtained with dental filling.
(a) Metallic artifacts obscure large parts of soft tissue.
(b) iMAR reduces artifacts, while significantly improving image quality.
Streak artifacts from high attenuation items are a familiar obstacle in CT imaging. These types of artifacts often appear in the form of metallic implants such as ortho implants, dental fillings, hip and knee prostheses, external life supporting equipment, radiotherapy markers etc. The artifacts not only obscure the CT images but also lead to misinterpretation in CT reporting.
SOMATOM go.Top Experience with iMAR
Figure 4: MPR CT images obtained with metal coin artifact from outside.
(a) Metallic artifacts creating large streak in soft tissue.
(b) iMAR reduces artifacts, while significantly improving image quality.

Conclusion

Various software and hardware-based techniques have been undertaken to reduce artifacts from metal. Siemens Healthineers iMAR is the apt technology to handle metal artifacts according to the type of implant. iMAR adapts its algorithm according to the type of implants (e.g. artificial joints, neuro coil, dental filling, pacemakers etc.). iMAR helps us to reduce metal artifacts in various body regions without increasing the radiation dose.
SOMATOM go.Top Experience with iMAR
Figure 5:
MPR CT images with spinal implants. Metallic artifacts from screw obscure large parts of anatomy. iMAR reduces artifacts, with significantly improving image quality.

Clinical Support:

Khaled Elshamy, CT Application Specialist
Siemens Healthineers, Egypt

References

1. E. Bar, A. Schwahofer, S. Kuchenbecker, and P. Haring. Improving radiotherapy planning in patients with metallic implants using iterative metal artifact reduction (iMAR) algorithm. Biomed. Phys. Eng. Express 1 (2015): 1-12 https://www.rsna.org/education/rg_cme.html, https://pubs.rsna.org/doi/full/10.1148/radiol.13122089
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