title: Noise reduction in MR angiography with nonlinear anisotropic filtering.
abstract: OBJECTIVE
  To evaluate three-dimensional nonlinear anisotropic filtering in suppressing image noise in high spatial resolution magnetic resonance angiograms (MRA) acquired with hybrid undersampled projection reconstruction and phase contrast vastly undersampled isotropic projection reconstruction (PC-VIPR).
  
  
  METHODS
  Three-dimensional nonlinear anisotropic filtering was quantitatively analyzed and evaluated through the measurement of contrast to noise ratio (CNR) in PC-VIPR images and contrast enhanced peripheral MRA images. To filter MRA images with ultra-high spatial resolution and poor CNR, a spatial frequency dependent nonlinear anisotropic filtering algorithm was proposed that uses two-step processing to filter the whole spatial frequency data.
  
  
  RESULTS
  Three-dimensional nonlinear anisotropic filtering was shown to be effective in suppressing noise and improving CNR in MRA with isotropic spatial resolution. Higher CNR was achieved using spatial frequency dependent nonlinear anisotropic filtering. A typical CNR gain of between 50-100% was shown in our studies.
  
  
  CONCLUSIONS
  Three-dimensional nonlinear anisotropic filtering significantly improved CNR in MRA images with isotropic spatial resolution. Spatial frequency dependent nonlinear anisotropic filtering further improved CNR for MRA images with ultra-high spatial resolution and low CNR.
authors.affiliation: Department of Medical Physics, University of Wisconsin, Madison, Wisconsin 53792-3252, USA. jiang@mr.radiology.wisc.edu
authors.forename: Jiang
authors.initials: J
authors.lastname: Du
authors.forename: Sean B
authors.initials: SB
authors.lastname: Fain
authors.forename: Tianliang
authors.initials: T
authors.lastname: Gu
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Grist
authors.forename: Charles A
authors.initials: CA
authors.lastname: Mistretta
mesh_terms: D016880:Anisotropy; D001808:Blood Vessels / Q000033:anatomy & histology; D005374:Filtration; D006801:Humans; D007089:Image Enhancement; D018810:Magnetic Resonance Angiography