Department of Biomedical Magnetic Resonance, Institute for Experimental Physics, Otto-von-Guericke University Magdeburg, Magdeburg, Germany.
MAGMA. 2012 Jun;25(3):183-92. doi: 10.1007/s10334-011-0275-6. Epub 2011 Aug 4.
This study presents an improved point-spread-function (PSF) mapping-based distortion correction method and accelerated PSF acquisition for distortion correction in EPI without loss of quality or reliability compared to full encoding.
To correct geometric distortions accurately, the PSF in the EPI phase-encoding coordinates (EPI-PSF) was measured and used as a kernel for distortion correction. FOV reduction was applied in the PSF mapping dimension for highly accelerated PSF acquisition. A novel approach for fold-over artifact correction in this reduced dimension is introduced. Conventional gradient-echo EPI and corresponding full PSF reference data were acquired in phantoms and in human brain at 7 T. The distortion corrected EPI data with the proposed acceleration were compared to result with full encoding. Previously published interpolation methods based on shift maps, non-uniform Fourier transformation and a b-spline interpolation were compared with the proposed method.
The results demonstrate that the proposed method corrects geometric distortions in EPI with high accuracy and quality despite the high acceleration. In contrast to partial parallel imaging acceleration, no noise enhancement is introduced.
The proposed EPI-PSF-based distortion correction improves correction of EPI and accelerates PSF reference data acquisition and computation.
本研究提出了一种改进的基于点扩散函数（PSF）映射的变形校正方法，并加速了 EPI 中的 PSF 获取，与全编码相比，在不降低质量或可靠性的情况下进行变形校正。
为了准确校正几何变形，测量了 EPI 相位编码坐标（EPI-PSF）中的 PSF 并将其用作失真校正的核。在 PSF 映射维度中应用视场减小以实现高度加速的 PSF 获取。引入了一种在这种减小维度中校正折叠伪影的新方法。在 7T 下的体模和人脑上采集了传统的梯度回波 EPI 和相应的全 PSF 参考数据。将具有所提出的加速的失真校正的 EPI 数据与全编码的结果进行比较。与所提出的方法相比，比较了基于移位图、非均匀傅立叶变换和 b 样条插值的先前发表的插值方法。
结果表明，尽管加速很高，但该方法可以高精度和高质量地校正 EPI 中的几何变形。与部分并行成像加速不同，不会引入噪声增强。
所提出的基于 EPI-PSF 的失真校正方法可改善 EPI 的校正，并加速 PSF 参考数据的获取和计算。
