title: Increased speed and image quality in single-shot fast spin echo imaging via variable refocusing flip angles.
abstract: OBJECTIVE
  To develop and validate clinically a single-shot fast spin echo (SSFSE) sequence utilizing variable flip angle refocusing pulses to shorten acquisition times via reductions in specific absorption rate (SAR) and improve image quality.
  
  
  METHODS
  A variable refocusing flip angle SSFSE sequence (vrfSSFSE) was designed and implemented, with simulations and volunteer scans performed to determine suitable flip angle modulation parameters. With Institutional Review Board (IRB) approval/informed consent, patients referred for 3T abdominal magnetic resonance imaging (MRI) were scanned with conventional SSFSE and either half-Fourier (n = 25) or full-Fourier vrfSSFSE (n = 50). Two blinded radiologists semiquantitatively scored images on a scale from -2 to 2 for contrast, noise, sharpness, artifacts, cardiac motion-related signal loss, and the ability to evaluate the pancreas and kidneys.
  
  
  RESULTS
  vrfSSFSE demonstrated significantly increased speed (∼2-fold, P < 0.0001). Significant improvements in image quality parameters with full-Fourier vrfSSFSE included increased contrast, sharpness, and visualization of pancreatic and renal structures with higher bandwidth technique (mean scores 0.37, 0.83, 0.62, and 0.31, respectively, P ≤ 0.001), and decreased image noise and improved visualization of renal structures when used with an equal bandwidth technique (mean scores 0.96 and 0.35, respectively, P < 0.001). Increased cardiac motion-related signal loss with full-Fourier vrfSSFSE was seen in the pancreas but not the kidney.
  
  
  CONCLUSIONS
  vrfSSFSE increases speed at 3T over conventional SSFSE via reduced SAR, and when combined with full-Fourier acquisition can improve image quality, although with some increased sensitivity to cardiac motion-related signal loss.
authors.affiliation: Department of Radiology, Stanford University School of Medicine, Stanford, California, USA.
authors.forename: Andreas M
authors.initials: AM
authors.lastname: Loening
authors.affiliation: Department of Radiology, Stanford University School of Medicine, Stanford, California, USA.
authors.forename: Manojkumar
authors.initials: M
authors.lastname: Saranathan
authors.affiliation: Department of Radiology, Stanford University School of Medicine, Stanford, California, USA.|Department of Diagnostic and Therapeutic Radiology, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand.
authors.forename: Nichanan
authors.initials: N
authors.lastname: Ruangwattanapaisarn
authors.affiliation: GE Healthcare Global MR Applications and Workflow, Rochester, Minnesota, USA.
authors.forename: Daniel V
authors.initials: DV
authors.lastname: Litwiller
authors.affiliation: GE Healthcare Global MR Applications and Workflow, Menlo Park, California, USA.
authors.forename: Ann
authors.initials: A
authors.lastname: Shimakawa
authors.affiliation: Department of Radiology, Stanford University School of Medicine, Stanford, California, USA.
authors.forename: Shreyas S
authors.initials: SS
authors.lastname: Vasanawala
mesh_terms: D000328:Adult; D000465:Algorithms; D017352:Echo-Planar Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D007668:Kidney / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D010179:Pancreas / Q000473:pathology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D013113:Spin Labels
chemical_list: D013113:Spin Labels
keywords: echo stabilization; single shot fast spin echo; specific absorption rate; variable refocusing flip angle