title: In-phase and out-of-phase gradient-echo imaging in abdominal studies: intra-individual comparison of three different techniques.
abstract: BACKGROUND
  T1-weighted gradient-echo in-phase and out-of-phase imaging is an essential component of comprehensive abdominal MR exams. It is useful for the study of fat-containing lesions and to identify various disease states related to the presence of fat in the liver.
  
  
  OBJECTIVE
  To compare three T1-weighted in-phase and out-of-phase (IP/OP) gradient-echo imaging sequences in an intra-individual fashion, and to determine whether advantages exist for each of these sequences for various patient types.
  
  
  METHODS
  One hundred and eighteen consecutive subjects (74 men, 44 women; mean age 53.9 ± 13.8 years) who had MRI examinations containing all three different IP/OP sequences (two-dimensional spoiled gradient-echo [2D-GRE], three-dimensional gradient-echo [3D-GRE], and magnetization-prepared gradient-recall echo [MP-GRE]) were included. Two different reviewers independently and blindly qualitatively evaluated IP/OP sequences to determine image quality, extent of artifacts, lesion detectability and conspicuity, and subjective grading of liver steatosis for the various sequences. Quantitative analysis was also performed. Qualitative and quantitative data were subjected to statistical analysis.
  
  
  RESULTS
  Respiratory ghosting, parallel imaging, and truncation artifacts as well as shading and blurring were more pronounced with 3D-GRE IP/OP imaging. Overall image quality was higher with 2D-GRE (P < 0.05). Detectability of low-fluid content lesions was lower with IP/OP MP-GRE sequences. MP-GRE sequences had the lowest SNRs (P < 0.001). Liver-to-spleen and liver-to-lesion CNRs were significantly lower with 3D-GRE and MP-GR, respectively (P < 0.001). Fat liver indexes showed strongly positive correlation between all sequences.
  
  
  CONCLUSIONS
  Currently, 2D-GRE remains the best approach for clinical IP/OP imaging. The good image quality of MP-GRE sequences acquired in a free-breathing manner should recommend its use in patients unable to suspend breathing.
authors.affiliation: Department of Radiology, University of North Carolina at Chapel Hill, USA.
authors.forename: Miguel
authors.initials: M
authors.lastname: Ramalho
authors.forename: Vasco
authors.initials: V
authors.lastname: Herédia
authors.forename: Rafael O P
authors.initials: RO
authors.lastname: de Campos
authors.forename: Brian M
authors.initials: BM
authors.lastname: Dale
authors.forename: Rafael M
authors.initials: RM
authors.lastname: Azevedo
authors.forename: Richard C
authors.initials: RC
authors.lastname: Semelka
mesh_terms: D000704:Analysis of Variance; D016477:Artifacts; D005234:Fatty Liver / Q000175:diagnosis; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008107:Liver Diseases / Q000175:diagnosis*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D012044:Regression Analysis; D012189:Retrospective Studies