title: High-frequency subband compressed sensing MRI using quadruplet sampling.
abstract: OBJECTIVE
  To present and validate a new method that formalizes a direct link between k-space and wavelet domains to apply separate undersampling and reconstruction for high- and low-spatial-frequency k-space data.
  
  
  METHODS
  High- and low-spatial-frequency regions are defined in k-space based on the separation of wavelet subbands, and the conventional compressed sensing problem is transformed into one of localized k-space estimation. To better exploit wavelet-domain sparsity, compressed sensing can be used for high-spatial-frequency regions, whereas parallel imaging can be used for low-spatial-frequency regions. Fourier undersampling is also customized to better accommodate each reconstruction method: random undersampling for compressed sensing and regular undersampling for parallel imaging.
  
  
  RESULTS
  Examples using the proposed method demonstrate successful reconstruction of both low-spatial-frequency content and fine structures in high-resolution three-dimensional breast imaging with a net acceleration of 11-12.
  
  
  CONCLUSIONS
  The proposed method improves the reconstruction accuracy of high-spatial-frequency signal content and avoids incoherent artifacts in low-spatial-frequency regions. This new formulation also reduces the reconstruction time due to the smaller problem size.
authors.affiliation: Department of Radiology, Stanford University, Stanford, California, USA; Department of Radiological Sciences, University of California Los Angeles, Los Angeles, California, USA.
authors.forename: Kyunghyun
authors.initials: K
authors.lastname: Sung
authors.forename: Brian A
authors.initials: BA
authors.lastname: Hargreaves
mesh_terms: D000465:Algorithms; D016477:Artifacts; D001943:Breast Neoplasms / Q000473:pathology*; D044962:Data Compression / Q000379:methods*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D015203:Reproducibility of Results; D018401:Sample Size; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D058067:Wavelet Analysis
keywords: compressed sensing; image reconstruction; iterative reconstruction; parallel imaging; wavelet transformation