title: Respiratory motion-corrected proton magnetic resonance spectroscopy of the liver.
abstract: OBJECTIVE
  To develop a post-processing, respiratory-motion correction algorithm for magnetic resonance spectroscopy (MRS) of the liver and to determine the incidence and impact of respiratory motion in liver MRS.
  
  
  METHODS
  One hundred thirty-two subjects (27 healthy, 31 with nonalcoholic fatty liver disease and 74 HIV-infected with or without hepatitis C) were scanned with free breathing MRS at 1.5 T. Two spectral time series were acquired on an 8-ml single voxel using TR/TE=2500 ms/30 ms and (1) water suppression, 128 acquisitions, and (2) no water suppression, 8 acquisitions. Individual spectra were phased and frequency aligned to correct for intrahepatic motion. Next, water peaks more than 50% different from the median water peak area were identified and removed, and remaining spectra averaged to correct for presumed extrahepatic motion. Total CH(2)+CH(3) lipids to unsuppressed water ratios were compared before and after corrections.
  
  
  RESULTS
  Intrahepatic-motion correction increased the signal to noise ratio (S/N) in all cases (median=11-fold). Presumed extrahepatic motion was present in 41% (54/132) of the subjects. Its correction altered the lipids/water magnitude (magnitude change: median=2.6%, maximum=290%, and was >5% in 25% of these subjects). The incidence and effect of respiratory motion on lipids/water magnitude were similar among the three groups.
  
  
  CONCLUSIONS
  Respiratory-motion correction of free breathing liver MRS greatly increased the S/N and, in a significant number of subjects, changed the lipids/water ratios, relevant for monitoring subjects.
authors.affiliation: Department of Radiology and Biomedical Imaging, University of California-San Francisco, San Francisco, CA, USA. sue@radiology.ucsf.edu
authors.forename: Susan M
authors.initials: SM
authors.lastname: Noworolski
authors.forename: Phyllis C
authors.initials: PC
authors.lastname: Tien
authors.forename: Raphael
authors.initials: R
authors.lastname: Merriman
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Vigneron
authors.forename: Aliya
authors.initials: A
authors.lastname: Qayyum
mesh_terms: D000328:Adult; D000465:Algorithms; D016477:Artifacts; D005234:Fatty Liver / Q000175:diagnosis* / Q000378:metabolism; D005260:Female; D006526:Hepatitis C / Q000175:diagnosis* / Q000378:metabolism; D006801:Humans; D008055:Lipids / Q000032:analysis*; D008099:Liver / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D011522:Protons; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D008055:Lipids; D011522:Protons