Department of Electrical Engineering, Magnetic Resonance Systems Research Laboratory, Stanford University, Stanford, California 94305-9510, USA.
Magn Reson Med. 2011 Aug;66(2):390-401. doi: 10.1002/mrm.22802. Epub 2011 Mar 7.
Non-Cartesian imaging provides many advantages in terms of flexibility, functionality, and speed. However, a major drawback to these imaging methods is off-resonance distortion artifacts. These artifacts manifest as blurring in spiral imaging. Common techniques that remove the off-resonance field inhomogeneity distortion effects are not sufficient, because the high order concomitant gradient fields are nontrivial for common imaging conditions, such as imaging 5 cm off isocenter in an 1.5 T scanner. Previous correction algorithms are either slow or do not take into account the known effects of concomitant gradient fields along with the field inhomogeneities. To ease the correction, the distortion effects are modeled as a non-stationary convolution problem. In this work, two fast and accurate postgridding algorithms are presented and analyzed. These methods account for both the concomitant field effects and the field inhomogeneities. One algorithm operates in the frequency domain and the other in the spatial domain. To take advantage of their speed and accuracy, the algorithms are applied to a real-time cardiac study and a high-resolution cardiac study. Both of the presented algorithms provide for a practical solution to the off-resonance problem in spiral imaging.
非笛卡尔成像是一种在灵活性、功能性和速度方面具有许多优势的技术。然而，这些成像方法的一个主要缺点是存在离频失真伪影。这些伪影表现为螺旋成像中的模糊。常见的去除离频场非均匀性失真效应的技术并不足够，因为在常见的成像条件下，如在 1.5T 扫描仪中离等中心 5 厘米处成像，伴随的高阶梯度场是非常复杂的。以前的校正算法要么速度慢，要么没有考虑到伴随梯度场以及场非均匀性的已知影响。为了简化校正，将失真效应建模为非平稳卷积问题。在这项工作中，提出并分析了两种快速而精确的后网格算法。这些方法同时考虑了伴随场效应和场非均匀性。一种算法在频域中运行，另一种在空域中运行。为了利用它们的速度和准确性，这些算法被应用于实时心脏研究和高分辨率心脏研究。所提出的两种算法都为螺旋成像中的离频问题提供了实用的解决方案。
