DISTORTION REDUCTION OF METAL ARTIFACTS IN MRI USING SHEAR CORRECTION

这个子项目是利用资源的许多研究子项目之一。 由NIH/NCRR资助的中心拨款提供。对子项目的主要支持 子项目的首席调查员可能是由其他来源提供的， 包括美国国立卫生研究院的其他来源。为子项目列出的总成本可能 表示该子项目使用的中心基础设施的估计数量， 不是由NCRR赠款提供给次级项目或次级项目工作人员的直接资金。 众所周知，由于敏感性效应，磁共振成像在金属周围是具有挑战性的[1]。磁化率的差异会导致 对于任意频移，这是造成失真和图像伪影的主要原因。我们的切片编码方法 金属伪影校正(SEMAC[2]通过使用额外的切片相位编码来校正切片失真，并校正读出 使用视角倾斜(VAT)造成的失真[3]。 VAT是一个简单的修改，包括在读出窗口期间播放用于激励的相同切片梯度。 这基本上是以这样一种方式倾斜体素，使得偏离共振的自旋看起来位于正确的位置 尊重共振自旋。 然而，存在与该方法相关联的限制：(A)读出窗口受限于切片的长度 梯度，这导致对读出占空比的限制，从而导致信噪比(SNR)效率的限制；(B)读出k- 空间被RF脉冲轮廓的形状有效地调制，这导致空间分辨率降低。 但保利已经证明，这种模糊可以通过使用二次相位RF和/或限制 读出窗口至RF脉冲的主瓣。 要了解卢卡斯中心正在进行的其他项目，请访问http://rsl.stanford.edu/(卢卡斯年度报告和 ISMRM 2011年摘要)

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)