title: Dynamic keyhole: a novel method to improve MR images in the presence of respiratory motion for real-time MRI.
abstract: OBJECTIVE
  In this work, the authors present a novel magnetic resonance imaging reconstruction method to improve the quality of MR images in the presence of respiratory motion for real-time thoracic image-guided radiotherapy.
  
  
  METHODS
  This new reconstruction method is called dynamic keyhole and utilizes a library of previously acquired, peripheral k-space datasets from the same (or similar) respiratory state in conjunction with central k-space datasets acquired in real-time. Internal or external respiratory signals are utilized to sort, match, and combine the two separate peripheral and central k-space datasets with respect to respiratory displacement, thereby reducing acquisition time and improving image quality without respiratory-related artifacts. In this study, the dynamic keyhole, conventional keyhole, and zero-filling methods were compared to full k-space acquisition (ground truth) for 60 coronal datasets acquired from 15 healthy human subjects.
  
  
  RESULTS
  For the same image-quality difference from the ground-truth image, the dynamic keyhole method reused 79% of the prior peripheral phase-encoding lines, while the conventional keyhole reused 73% and zero-filling 63% (p-value < 0.0001), corresponding to faster acquisition speed of dynamic keyhole for real-time imaging applications.
  
  
  CONCLUSIONS
  This study demonstrates that the dynamic keyhole method is a promising technique for clinical applications such as image-guided radiotherapy requiring real-time MR monitoring of the thoracic region. Based on the results from this study, the dynamic keyhole method could increase the temporal resolution by a factor of five compared with full k-space methods.
authors.affiliation: Radiation Physics Laboratory, Sydney Medical School, University of Sydney, Sydney 2006, Australia.
authors.forename: Danny
authors.initials: D
authors.lastname: Lee
authors.affiliation: Radiation Physics Laboratory, Sydney Medical School, University of Sydney, Sydney 2006, Australia.
authors.forename: Sean
authors.initials: S
authors.lastname: Pollock
authors.affiliation: Radiation Physics Laboratory, Sydney Medical School, University of Sydney, Sydney 2006, Australia.
authors.forename: Brendan
authors.initials: B
authors.lastname: Whelan
authors.affiliation: Radiation Physics Laboratory, Sydney Medical School, University of Sydney, Sydney 2006, Australia.
authors.forename: Paul
authors.initials: P
authors.lastname: Keall
authors.affiliation: Radiation Physics Laboratory, Sydney Medical School, University of Sydney, Sydney 2006, Australia.
authors.forename: Taeho
authors.initials: T
authors.lastname: Kim
mesh_terms: D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009038:Motion; D012119:Respiration; D013909:Thorax / Q000033:anatomy & histology / Q000502:physiology; D013997:Time Factors