title: Reverse retrospective motion correction.
abstract: One potential barrier for using prospective motion correction (PMC) in the clinic is the unpredictable nature of a scan because of the direct interference with the imaging sequence. We demonstrate that a second set of "de-corrected" images can be reconstructed from a scan with PMC that show how images would have appeared without PMC enabled.
  
  
  
  For three-dimensional scans, the effects of PMC can be undone by performing a retrospective reconstruction based on the inverse of the transformation matrix used for real time gradient feedback. Retrospective reconstruction is performed using a generalized SENSE approach with continuous head motion monitored using a single-marker optical camera system.
  
  
  
  Reverse retrospective reconstruction is demonstrated for phantom and in vivo scans using an magnetization-prepared rapid gradient echo (MPRAGE) sequence including parallel and Partial Fourier acceleration.
  
  
  
  Reverse retrospective reconstruction can almost perfectly undo the effects of prospective feedback, and thereby provide a second image data set with the effects of motion correction removed. In case of correct feedback, one can directly compare the quality of the corrected with that of the uncorrected scan. Additionally, because erroneous feedback during PMC may introduce artifacts, it is possible to eliminate artifacts in a corrupted scan by reversing the false gradient updates. Magn Reson Med 75:2341-2349, 2016. © 2015 Wiley Periodicals, Inc.
authors.affiliation: University of Hawaii, Department of Medicine, John A. Burns School of Medicine, Honolulu, Hawaii, USA.|Stanford University, Department of Radiology, Stanford, California, USA.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Zahneisen
authors.affiliation: University of Hawaii, Department of Medicine, John A. Burns School of Medicine, Honolulu, Hawaii, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Keating
authors.affiliation: University of Hawaii, Department of Medicine, John A. Burns School of Medicine, Honolulu, Hawaii, USA.
authors.forename: Aditya
authors.initials: A
authors.lastname: Singh
authors.affiliation: University of Hawaii, Department of Medicine, John A. Burns School of Medicine, Honolulu, Hawaii, USA.|Department of Radiology, University Medical Center Freiburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Herbst
authors.affiliation: University of Hawaii, Department of Medicine, John A. Burns School of Medicine, Honolulu, Hawaii, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Ernst
mesh_terms: D016477:Artifacts; D001921:Brain / Q000000981:diagnostic imaging; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results
keywords: optical tracking; prospective motion correction; retrospective motion correction; tracking errors