DISTORTION REDUCTION OF METAL ARTIFACTS IN MRI USING SHEAR CORRECTION

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Imaging around metal in MRI is known to be challenging due to susceptibility effects [1]. Susceptibility differences give rise to arbitrary frequency shifts which is the primary reason for distortion and image artifacts. Our method Slice Encoding for Metal Artifact Correction (SEMAC [2] correct for slice distortion by using extra slice phase-encoding, and correct for readout distortion by using view-angle tilting (VAT) [3]. VAT is a simple modification that comprises playing the same slice gradient used for excitation during the readout window. This essentially tilts the voxels in such a way that off-resonance spins appear to be located in the correct position with respect to on-resonance spins. There are, however, limitations associated with this method: (a) the readout window is limited to the length of the slice gradient, which leads to restrictions of the readout duty cycle and thus signal-to-noise (SNR) efficiency; (b) the readout k- space is effectively modulated by the shape of the RF pulse profile which results in reduced spatial resolution. Butts Pauly has shown that this blurring can be mitigated with the use of a quadratic phase RF and/or restricting the readout window to the main lobe of the RF pulse. To read about other projects ongoing at the Lucas Center, please visit http://rsl.stanford.edu/ (Lucas Annual Report and ISMRM 2011 Abstracts)