Learning objectives
To review some of the basic principles of imaging and how metal-induced susceptibility artifacts originate in MR images and methods to reduce it.
To provide an overview of various metal imaging methods in MRI and to understand the mechanism involved in it .
Background
The presence of metal can result in severe variations in the static magnetic field because of susceptibility variations between metal and surrounding tissue.
Magnetic susceptibility is the property which is determined by the way the object behaves in the presence of an external magnetic field. The magnetic field and metal-tissue interactions , based on the objects ,are classified as follows :
Diamagnetic materials
Paramagnet materials
Ferromagnet materials
1. Diamagnet Materials
These materials when placed in the magnetic field are mildly magnetized in a direction opposite...
Findings and procedure details
Metal artifacts can be broadly classified into In Plane and Through plane artifacts based on the plane of distribution of the artifact.(Fig 2)
IN PLANE ARTIFACTS: These artifacts appear along the direction of slice selection gradient.
Signal loss & Pile up
Near metal objects, the magnetic field variations can be very rapid, such that the magnetization within a voxel precesses at varying rates. This leads to intra voxel dephasingbecause oflarge susceptibility difference between the tissue and metal. This results in loss of coherence andsignal.(Fig 3)...
Conclusion
The metal artifact reduction techniques appears to hold great promise for significantly reducing both signal void and geometric distortion surrounding metallic implants in the body and therefore it is important to understand the cause of artifacts and to select the most appropriate of the available options.
Personal information and conflict of interest
C. Rasagna; Chennai/IN - nothing to disclose F. Abubacker Sulaiman; Chennai, TN/IN - nothing to disclose A. Rajendran; Chennai, TA/IN - nothing to disclose A. Asokan; Kelambakkam/Chennai, TA/IN - nothing to disclose
References
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4)Hargreaves BA, Worters PW, Pauly KB, Pauly JM, Koch KM, Gold GE. Metal-induced artifacts in MRI....
