Experimental and computational analyses of the effects of slice distortion from a metallic sphere in an MRI phantom
Experimental and computational analyses of the effects of slice distortion from a metallic sphere in an MRI phantom
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DOI：
10.1016/j.mri.2006.04.019
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发表时间：
2006-10-01
影响因子：
2.5
通讯作者：
Wehrli, Felix W.
中科院分区：
文献类型：
--
作者：
Hopper, Tim A. J.;Vasilic, Branimir;Wehrli, Felix W.
金属假体引起的磁敏感伪影是临床磁共振成像中的一个主要问题。我们从理论上和实验上分析切片变形所产生的敏感性差异，在一个由不锈钢球轴承嵌入琼脂糖凝胶组成的幻影。为了将观察到的图像伪影与切片失真联系起来，我们模拟了由2D和3D自旋回波（SE）和视角倾斜（VAT）序列产生的图像。当存在金属假体时，二维SE序列会遭受极端的切片失真，这与3D SE序列不同-因为切片是相位编码的-切片轮廓的失真被最小化，只要所选厚片大于感兴趣区域。在VAT序列中，通过在读出期间沿切片方向沿着应用梯度来减少伪影。但是，VAT不能校正激励切片轮廓，这会导致在期望切片位置之外激励自旋，并可能导致MR图像中的解剖信息不正确。我们建议在金属假体存在下进行成像的最佳序列利用3D采集，用相位编码代替切片选择以最大限度地减少切片失真，结合最大值的激励和读出梯度强度。(C)2006年爱思唯尔公司All rights reserved.
Susceptibility artifacts due to metallic prostheses are a major problem in clinical magnetic resonance imaging. We theoretically and experimentally analyze slice distortion arising from susceptibility differences in a phantom consisting of a stainless steel ball bearing embedded in agarose gel. To relate the observed image artifacts to slice distortion, we simulate images produced by 2D and 3D spin-echo (SE) and a view angle tilting (VAT) sequence. Two-dimensional SE sequences suffer from extreme slice distortion when a metal prosthesis is present, unlike 3D SE sequences for which - since slices are phase-encoded - distortion of the slice profile is minimized, provided the selected slab is larger than the region of interest. In a VAT sequence, artifacts are reduced by the application of a gradient along the slice direction during readout. However, VAT does not correct for the excitation slice profile, which results in the excitation of spins outside the desired slice location and can lead to incorrect anatomical information in MR images. We propose that the best sequences for imaging in the presence of a metal prosthesis utilize 3D acquisition, with phase encoding replacing slice selection to minimize slice distortion, combined with excitation and readout gradient strengths at their maximum values. (C) 2006 Elsevier Inc. All rights reserved.