title: Effect of flip angle for optimization of image quality of gadoxetate disodium-enhanced biliary imaging at 1.5 T.
abstract: OBJECTIVE
  The purpose of this study was to perform a qualitative and quantitative comparison of image quality of gadoxetate disodium-enhanced imaging of the biliary system acquired using different flip angles (FAs).
  
  
  METHODS
  Thirty-two patients (21 men and 11 women; mean [± SD] age, 51 ± 16 years) who underwent gadoxetate disodium-enhanced 1.5-T MRI were included. A 3D fat-suppressed T1-weighted gradient-echo sequence was acquired during the hepatobiliary phase using FAs of 12°, 25°, and 40°. One radiologist, who was blinded to FA, measured signal-to-noise ratios (SNRs) and contrast-to-noise ratios (CNRs) of the biliary tree. Two other blinded radiologists assessed subjective biliary duct clarity, overall image quality, background signal suppression, and ghosting artifact from the biliary tree using a scale of 1 to 4.
  
  
  RESULTS
  SNRs and CNRs of the common bile duct were significantly higher for FAs of 25° (227.5 ± 113.2 and 191.0 ± 102.2, respectively) and 40° (239.6 ± 118.7 and 201.7 ± 107.7, respectively) than for 12° (168.9 ± 73.9 and 126.7 ± 59.7, respectively; all p < 0.001). There were no significant differences in SNR or CNR between FAs of 25° and 40° (p ≥ 0.360). Clarity of first-, second-, and third-order intrahepatic ducts, background signal suppression, and overall image quality were significantly higher for both readers for FAs of 25° and 40° than for 12° (all p ≤ 0.031). None of these comparisons was significantly different for either reader between FAs 25° and 40° (all p ≥ 0.091), aside from improved depiction of third-order ducts at 40° for one reader (p = 0.030). Biliary ghosting artifact was significantly worse at 40° than at 12° for both readers (p ≤ 0.016).
  
  
  CONCLUSIONS
  The use of an FA larger than the clinical standard of approximately 12° has the potential to improve the image quality of gadoxetate disodium-enhanced biliary imaging.
authors.affiliation: Department of Radiology, New York University School of Medicine, 560 First Ave, TCH-HW 202, New York, NY 10016, USA. sooah.kim@nyumc.org
authors.forename: Sooah
authors.initials: S
authors.lastname: Kim
authors.forename: Thais C
authors.initials: TC
authors.lastname: Mussi
authors.forename: Lawrence J
authors.initials: LJ
authors.lastname: Lee
authors.forename: Elizabeth V
authors.initials: EV
authors.lastname: Mausner
authors.forename: Kyunghee C
authors.initials: KC
authors.lastname: Cho
authors.forename: Andrew B
authors.initials: AB
authors.lastname: Rosenkrantz
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001652:Bile Ducts / Q000473:pathology*; D003287:Contrast Media; D005260:Female; D019786:Gadolinium DTPA; D006500:Hepatic Duct, Common / Q000473:pathology; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D008107:Liver Diseases / Q000175:diagnosis; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged
chemical_list: D003287:Contrast Media; C073590:gadolinium ethoxybenzyl DTPA; D019786:Gadolinium DTPA