title: Enhancement of respiratory navigator-gated three-dimensional spoiled gradient-recalled echo sequence with variable flip angle scheme.
abstract: OBJECTIVE
  To develop and demonstrate the feasibility of a new technique for respiratory-gated, fat-suppressed, three-dimensional spoiled gradient-recalled echo (3D-SPGR) with navigator gating for more accurate and robust motion detection.
  
  
  METHODS
  A navigator-gated 3D-SPGR technique was modified to include a wait period immediately prior to the navigator sequence for magnetization recovery. Furthermore, a variable flip angle scheme was realized by a combination of ramp-up, ramp-down, and attenuation strategies for optimizing point spread functions. Phantom and human experiments were conducted with our technique on 1.5T scanners.
  
  
  RESULTS
  Using the method, T1-weighted 3D images with improved signal homogeneity were acquired with a maximum flip angle of 30° in phantom and human tests. Also, compared with the conventional navigator-gated 3D-SPGR, accurate respiratory motion detection of free-breathing subjects was provided, leading to reduced motion artifacts.
  
  
  CONCLUSIONS
  The combination of wait insertion and the variable flip angle method improved both motion detection accuracy and image homogeneity in a navigator-gated 3D-SPGR study.
authors.affiliation: Global Applied Science Laboratory, GE Healthcare, Hino, Tokyo, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Iwadate
authors.forename: Anja C S
authors.initials: AC
authors.lastname: Brau
authors.forename: Shreyas S
authors.initials: SS
authors.lastname: Vasanawala
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kabasawa
mesh_terms: D016477:Artifacts; D003198:Computer Simulation; D003287:Contrast Media / Q000008:administration & dosage; D005240:Feasibility Studies; D019786:Gadolinium DTPA / Q000008:administration & dosage; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D021621:Imaging, Three-Dimensional; D008099:Liver / Q000033:anatomy & histology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D055425:Respiratory-Gated Imaging Techniques
chemical_list: D003287:Contrast Media; C073590:gadolinium ethoxybenzyl DTPA; D019786:Gadolinium DTPA
keywords: liver imaging; magnetic resonance; navigator; spoiled gradient-recalled echo; variable flip angle