title: Hexagonal undersampling for faster MRI near metallic implants.
abstract: OBJECTIVE
  Slice encoding for metal artifact correction acquires a three-dimensional image of each excited slice with view-angle tilting to reduce slice and readout direction artifacts respectively, but requires additional imaging time. The purpose of this study was to provide a technique for faster imaging around metallic implants by undersampling k-space.
  
  
  METHODS
  Assuming that areas of slice distortion are localized, hexagonal sampling can reduce imaging time by 50% compared with conventional scans. This work demonstrates this technique by comparisons of fully sampled images with undersampled images, either from simulations from fully acquired data or from data actually undersampled during acquisition, in patients and phantoms. Hexagonal sampling is also shown to be compatible with parallel imaging and partial Fourier acquisitions. Image quality was evaluated using a structural similarity (SSIM) index.
  
  
  RESULTS
  Images acquired with hexagonal undersampling had no visible difference in artifact suppression from fully sampled images. The SSIM index indicated high similarity to fully sampled images in all cases.
  
  
  CONCLUSIONS
  The study demonstrates the ability to reduce scan time by undersampling without compromising image quality.
authors.affiliation: Department of Radiology, Stanford University, Stanford, California, USA; Department of Electrical Engineering, Stanford University, Stanford, California, USA.
authors.forename: Bragi
authors.initials: B
authors.lastname: Sveinsson
authors.forename: Pauline W
authors.initials: PW
authors.lastname: Worters
authors.forename: Garry E
authors.initials: GE
authors.lastname: Gold
authors.forename: Brian A
authors.initials: BA
authors.lastname: Hargreaves
mesh_terms: D000465:Algorithms; D016477:Artifacts; D003627:Data Interpretation, Statistical; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D016247:Information Storage and Retrieval / Q000379:methods; D007595:Joint Prosthesis; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D008670:Metals; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D018401:Sample Size; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted
chemical_list: D008670:Metals
keywords: SEMAC; artifacts; metallic implants; parallel imaging; undersampling