title: Water-fat separation with IDEAL gradient-echo imaging.
abstract: OBJECTIVE
  To combine gradient-echo (GRE) imaging with a multipoint water-fat separation method known as "iterative decomposition of water and fat with echo asymmetry and least squares estimation" (IDEAL) for uniform water-fat separation. Robust fat suppression is necessary for many GRE imaging applications; unfortunately, uniform fat suppression is challenging in the presence of B(0) inhomogeneities. These challenges are addressed with the IDEAL technique.
  
  
  METHODS
  Echo shifts for three-point IDEAL were chosen to optimize noise performance of the water-fat estimation, which is dependent on the relative proportion of water and fat within a voxel. Phantom experiments were performed to validate theoretical SNR predictions. Theoretical echo combinations that maximize noise performance are discussed, and examples of clinical applications at 1.5T and 3.0T are shown.
  
  
  RESULTS
  The measured SNR performance validated theoretical predictions and demonstrated improved image quality compared to unoptimized echo combinations. Clinical examples of the liver, breast, heart, knee, and ankle are shown, including the combination of IDEAL with parallel imaging. Excellent water-fat separation was achieved in all cases. The utility of recombining water and fat images into "in-phase," "out-of-phase," and "fat signal fraction" images is also discussed.
  
  
  CONCLUSIONS
  IDEAL-SPGR provides robust water-fat separation with optimized SNR performance at both 1.5T and 3.0T with multicoil acquisitions and parallel imaging in multiple regions of the body.
authors.affiliation: Department of Radiology, University of Wisconsin, Madison, Wisconsin 53792, USA. sreeder@wisc.edu
authors.forename: Scott B
authors.initials: SB
authors.lastname: Reeder
authors.forename: Charles A
authors.initials: CA
authors.lastname: McKenzie
authors.forename: Angel R
authors.initials: AR
authors.lastname: Pineda
authors.forename: Huanzhou
authors.initials: H
authors.lastname: Yu
authors.forename: Ann
authors.initials: A
authors.lastname: Shimakawa
authors.forename: Anja C
authors.initials: AC
authors.lastname: Brau
authors.forename: Brian A
authors.initials: BA
authors.lastname: Hargreaves
authors.forename: Garry E
authors.initials: GE
authors.lastname: Gold
authors.forename: Jean H
authors.initials: JH
authors.lastname: Brittain
mesh_terms: D000273:Adipose Tissue / Q000033:anatomy & histology*; D000465:Algorithms; D000843:Ankle Joint / Q000033:anatomy & histology; D016477:Artifacts; D001834:Body Water; D001940:Breast / Q000033:anatomy & histology; D017352:Echo-Planar Imaging / Q000379:methods*; D005260:Female; D006321:Heart / Q000033:anatomy & histology; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D007719:Knee Joint / Q000033:anatomy & histology; D016018:Least-Squares Analysis; D008099:Liver / Q000033:anatomy & histology / Q000473:pathology; D008280:Magnetics; D019047:Phantoms, Imaging; D012016:Reference Values; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted