title: Estimating absolute-phase maps using ESPIRiT and virtual conjugate coils.
abstract: To develop an ESPIRiT-based method to estimate coil sensitivities with image phase as a building block for efficient and robust image reconstruction with phase constraints.
  
  
  
  ESPIRiT is a new framework for calibration of the coil sensitivities and reconstruction in parallel magnetic resonance imaging. Applying ESPIRiT to a combined set of physical and virtual conjugate coils (VCC-ESPIRiT) implicitly exploits conjugate symmetry in k-space similar to VCC-GRAPPA. Based on this method, a new post-processing step is proposed for the explicit computation of coil sensitivities that include the absolute phase of the image. The accuracy of the computed maps is directly validated using a test based on projection onto fully sampled coil images and also indirectly in phase-constrained parallel-imaging reconstructions.
  
  
  
  The proposed method can estimate accurate sensitivities which include low-resolution image phase. In case of high-frequency phase variations VCC-ESPIRiT yields an additional set of maps that indicates the existence of a high-frequency phase component. Taking this additional set of maps into account can improve the robustness of phase-constrained parallel imaging.
  
  
  
  The extended VCC-ESPIRiT is a useful tool for phase-constrained imaging. Magn Reson Med 77:1201-1207, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
authors.affiliation: Institute for Diagnostic and Interventional Radiology, University Medical Center Göttingen, Göttingen, Germany.|German Centre for Cardiovascular Research (DZHK), Partner site Göttingen, Göttingen, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Uecker
authors.affiliation: Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, California, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Lustig
mesh_terms: D000465:Algorithms; D002138:Calibration; D019544:Equipment Failure Analysis / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000295:instrumentation* / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014159:Transducers
keywords: ESPIRiT; parallel imaging; partial Fourier; virtual coil