On the influence of zero-padding on the nonlinear operations in Quantitative Susceptibility Mapping

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• 作者：Sarah Eskreis-Winkler^a ; Dong Zhou^a ; Tian Liu^b ; Ajay Gupta^a ; Susan A. Gauthier^c ; Yi Wang^a ; Pascal Spincemaille^a ; ^{pas2018@med.cornell.edu}
• 关键词：QSM ; Quantitative susceptibility mapping ; GRE ; gradient echo ; PDF ; Projection onto Dipole Fields ; MEDI ; morphology enabled dipole inversion ; ROI ; region of interest ; PSF ; point spread function ; FWHM ; full-width-half-maximum ; PCOS ; projection onto convex sets
• 刊名：Magnetic Resonance Imaging
• 出版年：2017
• 出版时间：January 2017
• 年：2017
• 卷：35
• 期：Complete
• 页码：154-159
• 全文大小：1062 K
• 卷排序：35

文摘

Zero padding is a well-studied interpolation technique that improves image visualization without increasing image resolution. This interpolation is often performed as a last step before images are displayed on clinical workstations. Here, we seek to demonstrate the importance of zero padding before rather than after performing non-linear post-processing algorithms, such as Quantitative Susceptibility Mapping (QSM). To do so, we evaluate apparent spatial resolution, relative error and depiction of multiple sclerosis (MS) lesions on images that were zero padded prior to, in the middle of, and after the application of the QSM algorithm.Materials and MethodsHigh resolution gradient echo (GRE) data were acquired on twenty MS patients, from which low resolution data were derived using k-space cropping. Pre-, mid-, and post-zero padded QSM images were reconstructed from these low resolution data by zero padding prior to field mapping, after field mapping, and after susceptibility mapping, respectively. Using high resolution QSM as the gold standard, apparent spatial resolution, relative error, and image quality of the pre-, mid-, and post-zero padded QSM images were measured and compared.ResultsBoth the accuracy and apparent spatial resolution of the pre-zero padded QSM was higher than that of mid-zero padded QSM (p < 0.001; p < 0.001), which was higher than that of post-zero padded QSM (p < 0.001; p < 0.001). The image quality of pre-zero padded reconstructions was higher than that of mid- and post-zero padded reconstructions (p = 0.004; p < 0.001).ConclusionZero padding of the complex GRE data prior to nonlinear susceptibility mapping improves image accuracy and apparent resolution compared to zero padding afterwards. It also provides better delineation of MS lesion geometry, which may improve lesion subclassification and disease monitoring in MS patients.