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Characterizing the limits of MRI near metallic prostheses
Author(s) -
Smith Matthew R.,
Artz Nathan S.,
Wiens Curtis,
Hernando Diego,
Reeder Scott B.
Publication year - 2015
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.25540
Subject(s) - spins , excitation , multispectral image , bandwidth (computing) , image resolution , magnetic resonance imaging , dipole , nuclear magnetic resonance , computer science , materials science , physics , optics , radiology , artificial intelligence , telecommunications , medicine , quantum mechanics , condensed matter physics
Purpose To characterize the fundamental limits of MRI near metallic implants on RF excitation, frequency encoding, and chemical shift–encoding water–fat separation. Methods Multicomponent three‐dimensional (3D) digital models of a total hip and a total knee replacement were used to construct material‐specific susceptibility maps. The fundamental limits and spatial relationship of imaging near metallic prostheses were investigated as a function of distance from the prosthetic surface by calculating 3D field map perturbations using a well‐validated k‐space based dipole kernel. Results Regions limited by the bandwidth of RF excitation overlap substantially with those fundamentally limited by frequency encoding. Rapid breakdown of water–fat separation occurs once the intravoxel off‐resonance exceeds ∼6 ppm over a full range of fat fractions (0%–100%) and SNR (5–100). Conclusion Current 3D multispectral imaging methods would not benefit greatly from exciting spins beyond ±12 kHz despite the presence of signal that lies outside of this range from tissue directly adjacent to the metallic implants. Methods such as phase encoding in all three spatial dimensions are necessary to spatially resolve spins beyond an excitation bandwidth of ±12 kHz. The approach described in this study provides a benchmark for the capabilities of current imaging techniques to guide development of new MRI methods for imaging near metal. Magn Reson Med 74:1564–1573, 2015. © 2014 Wiley Periodicals, Inc.