title: On the influence of zero-padding on the nonlinear operations in Quantitative Susceptibility Mapping.
abstract: 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.
  
  
  
  High 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.
  
  
  
  Both 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).
  
  
  
  Zero 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.
authors: Department of Radiology, Weill Cornell Medicine, 525 East 70th Street, New York, NY, USA.
authors: Sarah
authors: S
authors: Eskreis-Winkler
authors: Department of Radiology, Weill Cornell Medicine, 525 East 70th Street, New York, NY, USA.
authors: Dong
authors: D
authors: Zhou
authors: Medimagemetric, LLC, 445 Main St, #7H, New York, NY, USA.
authors: Tian
authors: T
authors: Liu
authors: Department of Radiology, Weill Cornell Medicine, 525 East 70th Street, New York, NY, USA.
authors: Ajay
authors: A
authors: Gupta
authors: Department of Neurology, Weill Cornell Medicine, 525 East 68th Street, PO Box 117, New York, NY, USA.
authors: Susan A
authors: SA
authors: Gauthier
authors: Department of Radiology, Weill Cornell Medicine, 525 East 70th Street, New York, NY, USA.
authors: Yi
authors: Y
authors: Wang
authors: Department of Radiology, Weill Cornell Medicine, 525 East 70th Street, New York, NY, USA. Electronic address: pas2018@med.cornell.edu.
authors: Pascal
authors: P
authors: Spincemaille
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D001921:Brain / Q000000981:diagnostic imaging* / Q000473:pathology; D005069:Evaluation Studies as Topic; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000000981:diagnostic imaging* / Q000473:pathology; D015203:Reproducibility of Results; D012189:Retrospective Studies
keywords: Microstructure; Multiple sclerosis; Nonlinearity; Quantitative susceptibility mapping (QSM); Zero padding